genetics The basics Genetics is the study of heredity
Genetics is the study of heredity. The foundation for this branch of science was laid by Gregor Mendel ( ). Hereditary traits or characteristics are determined by units called genes (Mendel called these 'factors'). We know that genes are sections of DNA that can direct the cell to make a particular protein. A gene for a particular trait (for example height) can have different results or 'expressions'(for example tall or short). Alternative forms of a gene are called alleles. Letters of the alphabet can be used to represent the alleles (for examples Tfor tall and I for short). In the body cells of an organism, chromosomes are found in homologous pairs. Genes for a particular trait (feature) are found on both chromosomes exactly at the same location (locus). When an organism produces gametes, each gamete receives only one chromosome from the pair. When alleles are identical, we say the gene pair is homozygous (for example TTfor tall or tt for short). When an organism has two different forms of the allele, we call the gene pair heterozygous (for example Tt heterozygous tall). All true breeding or pure breeding organisms are homozygous for that particular trait. In a heterozygous gene pair, the allele which expresses itself is called the dominant allele and the allele whose expression is hidden by the dominant allele is called the recessive allele. The dominant allele is usually represented by an upper-case letter and the recessive allele is represented by the corresponding lower-case letter. The genetic make-up of an organism (or simply the genetic formula) is called its genotype (for example TT, Tt, tt). The expression of an allele is called its phenotype (for example tall, short). Across between two organisms of the same species (male and female) to study the inheritance of a particular trait is called a monohybrid cross. Below is an example of a simple monohybrid cross. This is one of the experiments conducted by Mendel on garden peas. Two parent plants were selected. One was true breeding (homozygous) for round seeds and the other parent was true breeding for wrinkled seeds. The allele for round seed is R and the allele for wrinkled seed is r. Mendel crossed these plants by dusting the pollen from one plant onto the stigma of the other plant. He then collected all the seeds and planted them to study the first generation of offspring. He called them the first filial generation or FI generation. All the plants from this cross produced round seeds. This is one of the experiments conducted by Mendel on garden peas.
Two parent plants were selected. One was true breeding (homozygous) for round seeds and the other parent was true breeding for wrinkled seeds. The allele for round seed is R and the allele for wrinkled seed is r. Mendel crossed these plants by dusting the pollen from one plant onto the stigma of the other plant. He then collected all the seeds and planted them to study the first generation of offspring. He called them the first filial generation or FI generation. All the plants from this cross produced round seeds. He then allowed the F1 plants (heterozygous round-seeded plants) to self-fertilise. The offspring produced by this cross, the F2 generation, contained round-seeded and wrinkled- seeded plants in a definite ratio (3:1 ). The dark colour of this mouse is due to a dominant allele, C
The dark colour of this mouse is due to a dominant allele, C. The alternate allele is c. In its homozygous state cc produces a white coat colour. State the genotype of this black mouse. State the phenotype of this mouse State whether this mouse is homozygous or heterozygous This mouse has an allele for black colour and an allele for white colour but its coat colour is black. Give a reason for this. 5 State what the genotype of a homozygous black mouse would be.
6 State what the genotype of a white mouse would be. What is the genotype of A What is the genotype of A
Answer Dd. This is because the offspring of A and B have both types of chin AND YET both parents have only one type of chin, so the parents must be heterozygous. What is dominant? Shaded or clear? Why? The grey is dominant because the offspring of F and G are both shadedand clear AND YET bothparents are shaded so they must be heterozygous and dominant. ans The allele for six fingers is probably dominant. All affected offspring have at least one affected parent, for example D, E and F all have six fingers and so did their mother/A from whom they received their affected allele (or H, I, J, K and L whose mother is D). in addition, it would not be possible for F and G to have M and O if the allele was recessive because M and O have 5 fingers and therefore, must have at least one normal/dominant allele which they cannot get from their parents who have 6 fingers. . answer Copy and answer Copy these and match with the terms
a.Gamete b Karyotype c Genome d Allele e Autosomes Each body cell of a mouse contains 40 chromosomes. Write down the number of chromosomes found in each type of cell shown below. a A sperm cell b An unfertilised egg c A muscle cell d a skin cell A mature sex cell having a single set of unpaired chromosomes. A pair of alternative forms of a gene that can occupy the same location (locus) on a particular chromosome and that control a particular characteristic. a chromosome that is not a sex chromosome. A complete set of an organisms genes; an organisms genetic material. A diagram of chromosomes of a cell arranged by size and centromere position The answer Copy these and match with the terms
a.Gamete b Karyotype c Genome d Allele e Autosomes Each body cell of a mouse contains 40 chromosomes. Write down the number of chromosomes found in each type of cell shown below. a A sperm cell b An unfertilised egg c A muscle cell d a skin cell A mature sex cell having a single set of unpaired chromosomes. A pair of alternative forms of a gene that can occupy the same location (locus) on a particular chromosome and that control a particular characteristic. a chromosome that is not a sex chromosome. A complete set of an organisms genes; an organisms genetic material. A diagram of chromosomes of a cell arranged by size and centromere position answer Copy and match these: Define chromosome. Define the term gene.
Describe the link between chromosomes and genes A structure found in the nucleus of a cell made up of DNA and protein carrying genes in a linear order. A section of DNA that acts as a unit of heredity. It directs the cell to manufacture a specific protein. sections of chromosomes. A long strand of DNA with special proteins holding it together. So, chemically both chromosome and +++++are the same, both made up of DNA. Copy and match these: Define chromosome. Define the term gene.
Describe the link between chromosomes and genes A structure found in the nucleus of a cell made up of DNA and protein carrying genes in a linear order. A section of DNA that acts as a unit of heredity. It directs the cell to manufacture a specific protein. sections of chromosomes. A long strand of DNA with special proteins holding it together. So, chemically both chromosome and genesare the same, both made up of DNA. Give the meanings of the following words.
1 Gene 2 Allele 3 Genotype 4 Phenotype 5 Dominant allele 6 Recessive allele 7 Homozygous 8 Heterozygous Print this A gardener bought some purple seeds from the garden centre
A gardener bought some purple seeds from the garden centre. Sometimes these types of seed are yellow. Explain what he could do to determine whether the corn seed he bought was homozygous or heterozygous. Use punnett squares to explain your answer. answer Cross the purple seed corn plant with yellow seed (homozygous recessive) corn plant. Collect all seeds and grow them to see the colour of seeds they bear. If all corn plants from this cross produced purple plants, the original corn plant will be homozygous dominant (PP). See Cross 1 next slide. If any of the corn plants from this cross produced yellow seeds, then the original corn plant will be heterozygous purple (Pp). See Cross 2. Ming breeds budgies as a hobby
Ming breeds budgies as a hobby. In her pet shop she has budgies of several colours - green, blue, grey and white. She keeps pedigree charts for each bird she sells. The following is a pedigree chart showing the inheritance of feather colours. State which characteristic, green or blue, is the dominant characteristic. Give two reasons for your answer. Answer: Green feather colour is dominant. If green feather is a recessive trait, there would be no chance of producing a blue budgie when two green budgies were crossed. Here, the two parent birds A and B both are green and two of its offspring 6 and 7 are blue feathered. There is a mixture of colours in the offspring so parents must be heterozygous . The diagrams below show two fruit flies A and B
The diagrams below show two fruit flies A and B. Fly A is heterozygous for its eye colour. Fly B is homozygous for its eye colour. Fly A has red eyes while fly B has brown eyes. The allele for red eye colour is R and the allele for brown eye colour is r. Copy and complete FLY A FLY B Phenotype Genotype True breeding Yes/No Shows dominant/ recessive trait? Alleles in gametes R or r (50%, 50%) Olo, who has normal hair, married Hessa.
Complete the punnett square diagram to show the chance of different coloured hair in their children. What is the chance that Hessa and Olos first child will have white forelock? Answer or 50% chance Qn: Cystic fibrosis is a hereditary disease that affects many glands in the body. This is a recessive condition in humans. The allele for cystic fibrosis can be represented by a and the allele for unaffected people is A. Pita and Tania have one normal child but their second child was affected by this condition. With the help of a punnett square diagram, explain how this occurred. Ans Pita and Tania are heterozygous for cystic fibrosis. They both have an allele for this condition that they can pass on to their offspring. Qn : There are several varieties of tomatoes available, including round and oblong tomatoes. The allele for oblong shape O is dominant over the allele for round shape o. In an experiment, a gardener pollinated the flower of a round tomato plant with the pollen from an oblong tomato plant. When the fruit ripened he collected 80 seeds. He planted these seeds and obtained the results as shown below. State the genotypes of the parent plants. a Round tomato b Oblong tomato 2 Complete the punnett square to show the probability of different offspring in such a cross. answer Queston: In meiosis explain why the number of chromosomes is halved. Answer The type of cell division is meiosis, the one responsible for the formation of gametes. During meiosis, homologous pairs of chromosomes pair up and then separate. As a result, the resulting cells receive only one set of chromosome. 2. Cell division by meiosis produces genetic variation. Explain how meiosis increases genetic variety and its significance. Answer. Since meiosis produces sex cells which are not all genetically identical, offspring produced by sexual reproduction or by the joining of two sex cells that have different genetic make up, shows variation. Variation plays a major role in natural selection and evolution. Variations increase the chance of survival of a species in a constantly changing environment. The diagram below shows the life cycle of cattle
The diagram below shows the life cycle of cattle. They have 60 chromosomes in their body cells. The circles represent the cells and the boxes represent the process involved in the production of cells. 1 Complete the diagram by writing down the numbers and words from the list below. Place chromosome numbers in each circle and the name of a process in each box. Discuss the importance of processes A, B and C in the life cycle of cattle. Answer:a. Meiosis produces gametes
Answer:a . Meiosis produces gametes. Meiosis reduces the number of chromosomes to 30. Exchange of genetic material occurs during meiosis produces variation among offspring. b. Fertilisation joins the male and female gametes. The original number of chromosome is thus regained. c.Mitosis occurs at this stage produces growth. Zygote is a single cell. This single cell divides to form an embryo. All cells in an embryo must have the same genetic material. This is achieved by mitosis at this stage. In male bears, black ears B is dominant over white ears b.
The genotype of a male bear is Bb. His mother has white ears. W h a t is the genotype of his mother? The male bear above mates witha w h i t e - eared female. Copy and complete the following cross diagram (Punnet Square) t o show the genotypes of the offspring that could result. In male bears, black ears B is dominant over white ears b.
The genotype of a male bear is Bb. His mother has white ears. W h a t is the genotype of his mother? Ans bb The male bear above mates witha w h i t e - eared female. Copy and complete the following cross diagram (Punnet Square) t o show the genotypes of the offspring that could result. bb b b Bb Bb bb bb The table below shows information about two pure bred houseflies.
W h a t is the genotype of t h e curly-winged fly? The phenotypebrittle bones in people is inherited. Brittleness is dominant (B) over non - brittle bones(b)- Four children have a father with non - brittle bones (genotype bb) and a mother with brittle bones (genotype Bb). a) What is the probability that any of t h e four children has brittle bones? b) In reality, none of the children havebrittle bones. How could this be so given your answer in a)? The table below shows information about two pure bred houseflies.
W h a t is the genotype of t h e curly-winged fly? Ans nn The phenotypebrittle bones in people is inherited. Brittleness is dominant (B) over non - brittle bones (b) -Four children have a father with non - brittle bones (genotype bb) and a mother with brittle bones (genotype Bb). a) What is the probability that any of t h e four children has brittle bones? 50% b) In reality, none of the children havebrittle bones. H o w could this be so given your answer in a)? ans This result is just a statistical result but in reality it can be different for a small sample Some dogs bark when following a scent, others are silent
Barking (B) is dominant to non-barking (b) A hunter owns a barker which he wants to use for breeding purposes but he wants to be sure it is a BB barker. What is the genotype of the bitch he should mate with this dog? The ability to roll the tongue is inherited. In the following family t r e e thewhich characteristic is dominant? What evidence supports your answerto a). If the dominant allele has the symbol R and the recessive allele has t h e symbol r, give the genotype of individual G. The children of A and B are heterozygous. W h i c h individual in the family t r e e shows that the n o n - roller allele exists in t h e children? Give a reason. F and G have another offspring. What is the probability of i t being a non-tongue roller? Some dogs bark when following a scent, others are silent
Barking (B) is dominant to non-barking (b) A hunter owns a barker which he wants to use for breeding purposes but he wants to be sure it is a BB barker. What is the genotype of the bitch he should mate with this dog? Ans He should mate it with a non-barking bb and if there are any offspring that can bark then he knows that his dog is Bb, but if there are all barking dog offspring then he knows that his dog is PROBABLY BB. The ability to roll the tongue is inherited. In the following family tree thewhich characteristic is dominant? Tongue rolling isdominant What evidence supports your answerto a). Because all the children of parents A and B are going to be heterozygous and so will show the dominant characteristic and that is rolling. If the dominant allele has the symbol R and the recessive allele has t h e symbol r, give the genotype of individual G. rr The ability to roll the tongue is inherited.
In the following family tree thewhich characteristic is dominant? Ans Tongue rolling isdominant What evidence supports your answerto a). Because all the children of parents A and B are going to be heterozygous and sho will sow the dominant characteristic and that is rolling. If the dominant allele has the symbol R and the recessive allele has t h e symbol r, give the genotype of individual G. Rr The children of A and B are heterozygous. W h i c h individual in the family t r e e shows that the n o n - roller allele exists in t h e children? Give a reason. Individual I This is because I has 2 different alleles and so got one from I . F and G have another offspring. What is the probability of i t being a non-tongue roller? 50% The following pedigree (called a 'family tree') shows the result of crossing two white animals. They produced a litter of six young ones, five white and one black. In these animals, coat colour is coded by a single pair of alleles (alternative forms of a single gene). The allele for white coat colour is represented by A. The allele for black coat colour is a. a) Give the genotype for each parent b) If the above cross was repeated many times, what would you expect to be the ratio of white and black individuals? c) If the black individual was crossed with a white homozygous individual, give the genotype and phenotype of their offspring. The following pedigree (called a 'family tree') shows the result of crossing two white animals. They produced a litter of six young ones, five white and one black. In these animals, coat colour is coded by a single pair of alleles (alternative forms of a single gene). The allele for white coat colour is represented by A. The allele for black coat colour is a. a) Give the genotype for each parent Ans Aa and Aa b) If the above cross was repeated many times, what would you expect to be the ratio of white and black individuals? ans 1:3 c) If the black individual was crossed with a white homozygous individual, give the genotype and phenotype of their offspring. All would be Aa and would be white. Two parents were known to be right-handed. They had three children
Two parents were known to be right-handed. They had three children. Sheila and Mary (identical twins) and Maurice. Right-handedness (R) is dominant to left-handedness (r). a) If Maurice is left-handed, what were the genotypes of the parents? b) What is the probability that Sheila is right handed? c) If Mary is right-handed, predict the handedness of Sheila. Two parents were known to be right-handed. They had three children
Two parents were known to be right-handed. They had three children. Sheila and Mary (identical twins) and Maurice. Right-handedness (R) is dominant to left-handedness (r). a) If Maurice is left-handed, what were the genotypes of the parents? Ans Rr b) What is the probability that Sheila is right handed? 75% c) If Mary is right-handed, predict the handedness of Sheila. Righthanded also In cats, short tails (S) are dominant over long tails (s).
A short-tailed female cat mates with a long-tailed male and produces a litter of I long-tailed and 7 short-tailed kittens. a) Give the genotype of each parent b) Out of 8 kittens, how many of them would you predict by theory to be long-tailed? c) The gene for short-tailed is said to be the 'dominant' gene. Explain what this means. A plant breeder crossed purebred red-flowered plants with purebred white flowered plants. All the offspring were red-flowered. D)The gene for red flowers is most likely to be: is it dominant or recessive? In cats, short tails (S) are dominant over long tails (s).
A short-tailed female cat mates with a long-tailed male and produces a litter of I long-tailed and 7 short-tailed kittens. a) Give the genotype of each parent Ans Female is Ss and male is ss b) Out of 8 kittens, how many of them would you predict by theory to be long-tailed? 50% so that would be 4 kittens c) The gene for short-tailed is said to be the 'dominant' gene. Explain what this means. ans There only needs to be one allele for the phenotype to be expressed. A plant breeder crossed purebred red-flowered plants with purebred white flowered plants. All the offspring were red-flowered. What isgene for red flowers is most likely to be: Dominant. In the garden-pea, white flower (w) is recessive to purple flower (W).
a) What is the phenotype of plant Ww? b) What is the genotype of a plant with white flowers? c) What is the genotype of a plant with purple flowers? In the garden-pea, white flower (w) is recessive to purple flower (W).
a) What is the phenotype of plant Ww? Ans purple b) What is the genotype of a plant with white flowers? ww c) What is the genotype of a plant with purple flowers? ans Ww or WW Colour blindness is a sex linked character
Colour blindness is a sex linked character. This means that it is caused by a gene which: A) is present in only one sex. B) causes secondary sexual features but is not found on t h e sex chromosome. C) does not cause sexual features but is found on t h e sex chromosome. D) causes primary sexual features. Colour blindness is a sex linked character
Colour blindness is a sex linked character. This means that it is caused by a gene which: A) is present in only one sex. B) causes secondary sexual features but is not found on t h e sex chromosome. C) does not cause sexual features but is found on t h e sex chromosome. D) causes primary sexual features. Colour-blindness is said t o be a sex-linked characteristic in people
Colour-blindness is said t o be a sex-linked characteristic in people. The following is a chart of t h e pedigree of the inheritance of colour-blindness in a family. Complete t h e following chart with the genotypes of the given phenotypes. Colour-blindness is said t o be a sex-linked characteristic in people
Colour-blindness is said t o be a sex-linked characteristic in people. The following is a chart of t h e pedigree of the inheritance of colour-blindness in a family. Complete t h e following chart with the genotypes of the given phenotypes. ans B b BB Bb bb In pea plants, flowers can be produced at the tip of the stem (called terminal flowers) or further down the stem (called axial flowers). Breeding between a plant with axial flowers and a plant with terminal flowers always produces offspring with axial flowers. Both parents are pure-breeding. Describe what pure-breeding means in terms of the type of alleles present. In pea plants, flowers can be produced at the tip of the stem (called terminal flowers) or further down the stem (called axial flowers). Breeding between a plant with axial flowers and a plant with terminal flowers always produces offspring with axial flowers. Both parents are pure-breeding. Describe what pure-breeding means in terms of the type of alleles present. Ans Has the same type of allele/is homozygous for one allele Explain why all the offspring have axial flowers using a fully labelled Punnett square and the symbols F and f to correctly represent the alleles.NB both parents are pure bred Explain why all the offspring have axial flowers using a fully labelled Punnett square and the symbols F and f to correctly represent the alleles. Ans Has parents as FF axial, ff terminal, offspring as Ff axial correct in Punnett square Plants with an FF genotype and an Ff genotype will both have axial flowers.
(c)Discuss how the genotype of a plant with axial flowers could be proven by doing a simple breeding experiment ..(terminal flowers) Ans Use a pure breed ff and if genotype of plant is FF all the (many) offspring will be plants with axial flowers. However, if Ff genotype then some offspring would show terminal flowers. You Should use a fully labelled Punnett Squares (a)Define the term homozygous.
(b)Using the letter L, give the genotype for a homozygous recessive individual (c)German shepherd dogs have 78 chromosomes. How many would they have in an egg cell? (a)Define the term homozygous.
Ans A genotype when the two alleles are the same (b)Using the letter L, give the genotype for a homozygous recessive individual ll (c)German shepherd dogs have 78 chromosomes. How many would they have in an egg cell? 39 chromosomes A homozygous short haired male German shepherd was mated with a long haired female German shepherd and all the pups were short haired. Complete the Punnett square for the cross showing the genotype of the pups A homozygous short haired male German shepherd was mated with a long haired female German shepherd and all the pups were short haired. Complete the Punnett square for the cross showing the genotype of the pups ans In pea plants, the allele for yellow seeds (G) is dominant to that for green seeds (g).
Describe what is meant by the terms dominant and recessive. Ans Dominant shows in phenotype and masks recessive: recessive only expressed if two copies of the allele are present. A heterozygous yellow-seed pea plant is crossed with another heterozygous yellow-seed pea plant.
Draw a Punnett square to show the genotypes of the offspring. A heterozygous yellow-seed pea plant is crossed with another heterozygous yellow-seed pea plant.
ans Explain the difference between genotype and phenotype
Explain the difference between genotype and phenotype. Use examples from your Punnett square in the last slide to help in your explanation. Ans Genotype is Gg/GG/gg: phenotype is yellow seeds/green seeds Kathleen is heterozygous for a condition that is carried on the X chromosome as a recessive trait.
(a)Describe the term heterozygous. Ans the 2 chromosomes carried have two different alleles for the gene. What is meant by the term recessive trait?
Ans a recessive trait is a characteristic that is expressed only if both alleles are recessive. Gottrons Syndrome is a rare recessive condition which causes people to develop small hands and small feet and age prematurely (early).Kathleens cousin has Gottrons Syndrome but her Uncle and Aunty do not have it. You have been asked to give a talk to your class to explain how this family could have produced a daughter with Gottrons Syndrome from parents who do not have it. Discuss how you would tell your class how this family ended up having a daughter with this condition.What is the chance of their next child also having this rare disease? Use a Punnet square to help with your answer Also need the punnet square
Gottrons Syndrome is a rare recessive condition which causes people to develop small hands and small feet and age prematurely (early).Kathleens cousin has Gottrons Syndrome but her Uncle and Aunty do not have it. You have been asked to give a talk to your class to explain how this family could have produced a daughter with Gottrons Syndrome from parents who do not have it. Discuss how you would tell your class how this family ended up having a daughter with this condition.What is the chance of their next child also having this rare disease? Use a Punnet square to help with your answer Ans Both parents were heterozygousand so masked a hidden gene so there is a 25% chance of next child getting it.Each parent gives 1 recessive allele which in the zygote is expressed as this disease . Also need the punnet square The diagram below shows that DNA is made
up of repeating units called nucleotides. Write the complementary base pairs G C A T The diagram below shows that DNA is made
up of repeating units called nucleotides. Answer TCGTA G C A T Gregor Mendel was a monk who studied the inheritance of different characteristics of pea plants.One characteristic he looked at was pea shape.He found round peas were dominant over wrinkled peas. Discuss the relationship between DNA, genes, alleles and chromosomes in the pea plants.You should: Explain the difference between genes and alleles. Ans A gene is a section of DNA/part of a chromosome that carries the instructions for a particular feature/to make a protein. An allele is the different/alternate form of a gene. In the example given, the gene for pea shape has two alleles, smooth and wrinkled. Gregor Mendel was a monk who studied the inheritance of different characteristics of pea plants.One characteristic he looked at was pea shape.He found round peas were dominant over wrinkled peas. Discuss the relationship between DNA, genes, alleles and chromosomes in the pea plants.You should: Explain how the information in the DNA determines the characteristics (eg. pea shape) and the different forms (variations) of that characteristic (eg. smooth and wrinkled peas).You may support your answer with a diagram. Ans The order of the DNA bases within a gene determines which protein is made. The differences in the base sequences of the alleles, for a particular gene, results in different features and variation shown in offspring. The order of the bases in the allele that codes for the smooth phenotype is different to the order of bases in the allele that codes for the wrinkled phenotype. The following pedigree chart shows the inheritance of wool colour in sheep:
Explain which characteristic, white or black wool, is recessive. Refer to specific sheep in the pedigree chart to support your answer. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Key: female male Black wool White wool Explain which characteristic, white or black wool, is recessive. Ans
The following pedigree chart shows the inheritance of wool colour in sheep: Explain which characteristic, white or black wool, is recessive. Ans Black wool colour is recessive because: Sheep 1 and 2 had 6 offspring and some were whitenumber 9 had black wool so 1 and 2 must be heterozygous white so black is recessive. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Key: female male Black wool White wool Using A to represent the dominant allele, and a to represent the recessive allele, give the probable genotype of sheep number 1. Ans Sheep 1 = Aa 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Key: female male Black wool White wool You may use diagrams to support your answer.
hSheep have 54 chromosomes in their body (somatic) cells.These cells are produced by a process called mitosis. Gametes are produced during meiosis, which is a type of cell division that produces genetic variation. Discuss how the sheep gametes produced are different to normal body cells.Your discussion should include: The number of chromosomes in sheep gametes compared with body (somatic) cells An explanation of 2 ways meiosis results in cells showing genetic variation. You may use diagrams to support your answer. Sheep have 54 chromosomes in their body (somatic) cells
Sheep have 54 chromosomes in their body (somatic) cells.These cells are produced by a process called mitosis. Gametes are produced during meiosis, which is a type of cell division that produces genetic variation. Ans The number of chromosomes in sheep gametes is half the number in sheep somatic cells the gametes of sheep have 27 chromosomes. Two processes in meiosis that result in gametes showing genetic variation are independent assortment and crossing over. During meiosis, the homologous chromosomes are randomly separated into gametes. It is random which daughter cell each homologue ends up in. Crossing over occurs when homologous chromosome pairs line up during meiosis and segments of homologous chromosomes are swapped resulting in chromosomes with different allele combinations. Spider lamb syndrome is a disease found in certain breeds of sheep in countries including New Zealand.It is caused by a recessive mutation and results in lambs with defects including abnormally long, spider-like legs, twisted spines and underdeveloped muscles.Lambs born with the condition do not normally survive to full maturity. Discuss how spider lamb syndrome is inherited even when both parents do not have the syndrome.You should: Complete the punnet square below showing the genotypes of the lambs produced when a ram and a ewe are mated, which are both heterozygous for the spider lamb syndrome alleles. Use A to represent the dominant allele and a to represent the recessive allele. Give the phenotype ratio of the lambs produced. Use the results of the punnet square to explain how lambs can inherit spider lamb syndrome. The lamb on the left has spider lamb syndrome and has abnormally long legs, compared with the normal lamb on the right. Discuss how spider lamb syndrome is inherited even when both parents do not have the syndrome.
Ans Phenotype ratio: 3 normal lambs:I lamb with spider lamb syndrome. Spider lamb syndrome is caused by a recessive mutation. This means lambs will only be born with the syndrome if they inherit two recessive alleles (aa). When two heterozygous parents mate (Aa) there is a 25% chance of a lamb being born with the syndrome. Both parents do not have the syndrome because even though they possess a recessive allele, (a) it is masked by the dominant allele (A). The lamb on the left has spider lamb syndrome and has abnormally long legs, compared with the normal lamb on the right. Aa aa AA Meiosis results in increased genetic variation within a population
Meiosis results in increased genetic variation within a population. Mutations can also result in increased genetic variation.Define mutation and explain why mutations can be considered the ultimate source of variation compared with variation resulting from meiosis. Ans A mutation is a (permanent) change/mistake in the DNA sequence. Mutations are the ultimate source of variation because they result in new alleles being added to a population.Mutations change the order of the DNA bases. Processes in meiosis result in genetically unique gametes but these processing are only reshuffling of existing genetic material. Independent assortment produces gametes with new combinations of chromosomes whereas crossing over produces new combinations of alleles on chromosomes. Explain the advantages of asexual reproduction in aphids
Aphids are one of the main organisms that live on rose bushes. They mainly feed on young buds and leaves.Aphid eggs live through the winter in protected nooks and crannies on the plant. In the spring, eggs hatch into females that are capable of reproducing without mating (asexual reproduction). In autumn, winged sexual forms (males and females) are produced. They mate, and the females lay eggs for overwintering. Aphids feed by piercing the plant and sucking up the liquids. They mainly feed on young buds and new leaves. Explain the advantages of asexual reproduction in aphids Explain the advantages of asexual reproduction in aphids.
Ans One advantage of asexual reproduction is that it is a fast method of reproduction. There is no need to find a mate and when favourable conditions arise in Spring, when food supply is optimal, many offspring can be produced to take advantage of the favourable environment. Another advantage of asexual reproduction is that offspring are genetically identical to the parent. Because the parent successfully exploited the rose bush habitat, the offspring are also likely to thrive. Aphids are one of the main organisms that live on rose bushes
Aphids are one of the main organisms that live on rose bushes. They mainly feed on young buds and leaves.Aphid eggs live through the winter in protected nooks and crannies on the plant. In the spring, eggs hatch into females that are capable of reproducing without mating (asexual reproduction). In autumn, winged sexual forms (males and females) are produced. They mate, and the females lay eggs for overwintering. Aphids feed by piercing the plant and sucking up the liquids. They mainly feed on young buds and new leaves. Sexual reproduction results in aphids that show genetic variation. Discuss why genetic variation is important for survival in a population of aphids. Sexual reproduction results in aphids that show genetic variation
Sexual reproduction results in aphids that show genetic variation. Discuss why genetic variation is important for survival in a population of aphids. Ans Genetic variation is important in a population for species survival in a changing environment. If the environment changes, or for example, a pesticide spray is used to kill the aphids, if there is variation in the population it increases the chance that some members of the population will survive and reproduce therefore ensuring survival of the species. The following is a pedigree of myopia (nearsightedness).
Individuals with myopia are shaded. Use the key below to classify the genotypes of individuals I- 6. Key: A Heterozygous B Homozygous C Not sufficientevidenceto determinegenotype Is the gene which produces myopia dominant or recessive.