Genetics

Genetics

Section 2: vocabulary:• 1. Genetics • 2. Allele: alternate forms of the gene • 3. Dominant : appears in the F1• 4. Recessive: not present in the F1 • 5. Homozygous : same alleles• 6. Heterozygous : different alleles• 7. Genotype: alleles • 8. Phenotype: physical • 9. Law of segregation • 10. Hybrid • 11. Law of independent assortment

• Additional Vocabulary

monohybrid cross true-breeding P generation F1 generation F2 generation

Punnett square test cross probability pedigree

sex-linked gene polygenic inheritance

incomplete dominance multiple alleles codominance

The “Father of Genetics”!

•Genetics: the science of heredity.

•Gregor Mendel

Gregor Johann Mendel (1822 - 1884) was a member of an Augustinian order (Monastic) in Brunn Austria

Mendel began studying plant breading by trying to find the effects

of crossing different strains of common garden pea

• He carried out his research with more precision than had yet been used. He also used the new science of statistics to analyze the results of his experiments. This use of mathematics to describe biological phenomena was a new concept.

• Gregor Mendel bred varieties of the garden pea in an attempt to understand heredity.

• Mendel observed that contrasting traits appear in offspring according to simple ratios.

genotype

• The organism’s allele pairs : what genes it has to produce the outward appearance it has.

Homozygous genotype

• An organism with two of the same alleles for a trail. Both alleles are the same

Dominant

Recessive

Heterozygous genotype

• An organism with 2 different alleles for a trait.

Hybrid 279

• Heterozygous genotypes

Phenotype

• The observable or outward expression of the allele pair that an organism has… what it “looks” like.

Monohybrid crosses

• Two parents differ by only one trait.

• Height tall or short

or

smooth/ wrinkled

Green/ yellow

Monohybrid traits

Monohybrid crosses

Results of a monohybrid crossfirst generation F1

• One of the characteristics would kind of “take over” the other and the offspring would all look like only one of the parents.

• Example: green and yellow

• All offspring were yellow!

Second generation F2

• When the parents from the F1 are crossed.

• Yellow X Yellow =

• ¾ were Yellow but ¼ was green .

• The green trait reappeared!!!!

• Mendel collected 6022 yellow peas and 2001 green.

• this was almost a perfect 3:1 ratio of yellow :green

• He studied several traits and each gave this ratio!

F2 generation

What did Mendel learn from this?

• Each organism has two factors for each of its traits.

• “Factors” are forms of the Genes on chromosomes.

• These are the alleles

alleles

• An alternative form of a single gene passed from generation to generation.

• Example: the yellow or the green form of the color of peas are each alleles of the gene for the color of peas.

• In Mendel’s experiments, only one of the two contrasting forms of a character was expressed in the F1 generation.

• The other form reappeared in the F2 generation in a 3:1 ratio

• Factors are Genes on chromosomes

• Forms are called : alleles

Rule of Dominance

• By definition,

• the trait that shows up in the F1 generation is dominant

• the trait that disappears is recessive

What do these mean?

•P

•F1

•F2

Out of Mendel's work came two "Laws" of inheritance:

• 1) Mendel proposed that heredity was controlled by paired factors that segregated when gametes formed and rejoined at fertilization and,

• 2) The principle of independent assortment indicates that the segregation of one pair of factors, or Alleles, has no influence over the way any other pair segregates.

Gregor Mendel approached problem-solving in new and

different ways.

• 1. He worked with pure strains of garden peas.

• The flowers have both male (stamen- anther and filaments) and female (pistil- stigma, style and ovary) reproductive parts.

• He removed (emasculated) the male part (anthers and filaments that produce the male sex cells) so he could control the way each plant was fertilized.

• This was done artificially by mechanically transferring the male sex cells from the desired plant to the stamen of the emasculated plant.

• The offspring using this procedure are referred to as "crosses".

• 2. He only worked with traits of the peas that could easily be seen.

• He experimented using only one trait at a time.

• Traits included a) stem length, b) flower color or c) seed shape.

• 3. Mendel kept detailed records of his "crosses".

• He counted the pea offspring and

calculated, using mathematics, how often the trait occurred in the offspring.

• Mendel believed that traits were determined by individual units called factors.

• He believed that each offspring received a factor from each parent.

• Today these factors are called genes.

Punnett Squares

• The square shows how the alleles separate when gametes are formed.

• It shows the possible combinations of the alleles when fertilization occurs.

Dad

Mom

Allele allele

Allele

Allele

Punnett Square• G= green peas g= yellow peas

pure breed greenG G

g

g

Pure breed yellow

What are the results?

• 100% are phenotype green

• 100% are genotype heterozygous

4/4

Both parents are: heterozygous genotype and brown hair

phenotype

What are the results?

= Brown hair

= blonde hair

Chances for Genotypes

1/4

2/4

1/4

Chances for Phenotypes

¼ blonde¾ Brown

Flower color

• R = red

• r = white

Mendel's First Law: Law of Segregation

• Mendel guessed that the TWO genes for flower color separate or segregate, when the sex cells form during meiosis.

• In the case of the hybrid pea flowers (RR), each plant would have one gene (allele) for red color (R) and one gene (allele) for white color (r).

• These two genes would separate or segregate from each other during the formation of the sex cells. About half of the sex cells would receive the gene for red color and the other half the gene for white color.

Meiosis/ sex cell formation

Sperm cells each get one allele

Mendel's Law of Segregation states-

• The two genes that determine a particular trait will separate when sex cells form.

• Half of the cells will receive one gene (allele) and half of the cells will receive the other gene (allele) of the allelic pair.

• _ The law of segregation states that the two alleles for a gene separate when gametes are formed.

Mendel's Second Law

• - the law of independent assortment;

• Random distribution of alleles occurs during gamete formation. Genes on separate chromosomes sort independently during meiosis.

• during gamete formation the segregation of the alleles of one allelic pair is independent of the segregation of the alleles of another allelic pair

• The law of independent assortment states that two or more pairs of alleles separate independently of one another during gamete formation.

In other words…

• Where the allele for color goes is not connected to where the gene for height goes.

Color

r

Height

T

Color

R

Height

t

Tt

R r

Tt t

rR

Mendel’s Theory

• _ Different versions of a gene are called alleles. An individual usually has two alleles for a gene, each inherited from a different parent.

• _ Individuals with the same two alleles for a gene are homozygous; those with two different alleles for a gene are heterozygous.

Studying Heredity

• _ The results of genetic crosses can be predicted with the use of Punnett squares and probabilities.

• _ A test cross can be used to determine whether an individual expressing a dominant trait is heterozygous or homozygous.

• _ A trait’s pattern of inheritance within a family can be determined by analyzing a pedigree.

Linked genes

• Unless……. The genes are located on the same chromosome and then they are called linked genes and they do travel together to the same gamete.

Genes on the same chromosome will always travel together into the

same gamete

• red hair r

• freckles f

2 traits

• Dihybrid cross

• When you look at two traits at a time the Punnett square gets bigger because the possible combinations get bigger!

dihybrid• A= attached ears

• a = unattached ears

• B= brown hair

• b= blonde hair

• So when we look at the chances of getting two traits the possibilities increase

Heterozygous= hybrid

• So 2 pure breed parents for both traits would be…

• P generation= AABB X aabb

• All of the “kids” would be AaBb

Dihybrid cross means hybrid for two traits so…

• F1 generation

•AaBb X AaBb

• What are the possible combinations of gametes?

• Remember the law of segregation only one “letter” or allele for a trait.

• Only A or a but not both!

A a B• The gene alleles for attached or

unattached ears must segregate from each other during meiosis.

• In other words…. You will only have one or the other in the gametes.

b

• The same is true for the alleles for hair color.

• gametes

a B bA

Possible gametes

•AB

• Ab

• aB

• ab

AaBb

Place the possible gametes on the sides of the square

AB Ab aB ab

AB

Ab

aB

ab

Which

becomes AABB

What are the phenotypic results?

• ___/16 attached ears and brown hair

• ___/16 attached ears and blonde hair

• ___/16 unattached ears and brown hair

• ___/16 unattached ears and blonde hair

You always get

•9:3:3:1

The genotypic results?• Homozygous dominant for both traits ___/16

• Heterozygous for both traits ___/16

• Homo recessive for both traits ___/16

• Homo dominant for first hetero for 2nd ___/16

• Homo recessive for 1st hetero for 2nd ___/16

• Homo recessive for 1st homo dom 2nd ___/16

• Hetero for 1st homo/dom for 2nd ___/16

• Hetero for 1st homo rec for 2nd ___/16

• Complete the list……

Section 3

Section 3 vocabulary:

1. Genetic recombination

2. Polyploidy

Genetic recombination

• New combinations of genes produced by crossing over and independent assortment.

• Add variations

• 2n n is the number of chromosome pairs

Gene linkage

• Genes close together on the same chromosome are said to be linked and travel together!

• These are exceptions to the independent assortment law!

• Crossing over happens more when genes are far apart than those that are close together.

• Chromosome maps show the location of genes on chromosomes.

Polyploidy

• One or more sets of chromosomes.

• Triploid organisms 3n have 3 sets

• this is rare in animals but more common in plants.

• In humans this is lethal… deadly!

• 1/3 plants are polyploids.

• Wheat, oats, sugar are all polyploids, this increases their vigor and size.

polyploid

Kleinfelder Karyotype

• Question #1 • Let's say that in seals, the gene for the length of

the whiskers has two alleles.  The dominant allele (W) codes long whiskers & the recessive allele (w) codes for short whiskers.

• a)  What percentage of offspring would be expected to have short whiskers from the cross of two long-whiskered seals, one that is homozygous dominant and one that is heterozygous? b) If one parent seal is pure long-whiskered and the other is short-whiskered, what percent of offspring would have short whiskers?

• P-sqARE PraCTice qUesTiON #2

• In purple people eaters, one-horn is dominant and no horns is recessive. Draw a Punnet Square showing the cross of a purple people eater that is hybrid for horns with a purple people eater that does not have horns. Summarize the genotypes & phenotypes of the possible offspring.

• Question 3

• A green-leafed luboplant (I made this plant up) is crossed with a luboplant with yellow-striped leaves.  The cross produces 185 green-leafed luboplants. Summarize the genotypes & phenotypes of the offspring that would be produced by crossing two of the green-leafed luboplants obtained from the initial parent plants.

P-squARE PRacTice qUeStION #4

• Mendel found that crossing wrinkle-seeded plants with pure round-seeded plants produced only round-seeded plants.  What genotypic & phenotypic ratios can be expected from a cross of a wrinkle-seeded plant & a plant heterozygous for this trait (seed appearance)?

Gene Linkage

• Genes on the same chromosome are linked. • Linked genes are inherited together. • Linked genes do not undergo independent

assortment. • THEREFORE, MENDELS LAW OF INDEPENDENT

ASSORTMENT ONLY IS TRUE IF THE GENES ARE ON DIFFERENT CHROMOSOMES.

• Studies have shown that linked genes on the same chromosome sometimes can separate. This occurs by a process called "crossing over".

•  

Crossing Over

– Occurs at prophase during the first part of meiosis (Anaphase I)

• Chromosomes pair before they divide • Chromosome pairs wind around each other • Each pair of chromosomes duplicates itself • Chromosomes break and exchange equal amounts

of chromosome material. The newly exchanged pieces are enzymatically "glued" together.

• Chromosomes separate (to individual chromatids). Each chromatid now has different traits or genes/alleles.

Purpose of crossing over:

• provides new combinations of genes/alleles (traits) in male and female sex cells (gametes) so that when fertilization occurs the offspring demonstrate increased genotypic and phenotypic variability.

Sex-linked genes

• Genes located on one of the sex chromosomes. Usually the X

• Most often expressed in males because they only have one X chromosome

• The inheritance of abnormal genes found on the 22 pairs of human chromosomes (autosomes) obey the principles of Mendelian genetics.

• The inheritance of abnormal genes on the X-chromosomes also are based on Mendel's principles.

Gender issues• complicate this process only in regard to

the Y chromosome.

• Males have only one X chromosome whereas females have a pair of X-chromosomes. The expression of genetic abnormalities in the offspring of affected people takes on a new dimension when the Y-chromosome is included in the "equation".  

•  

• Traits which are determined by one or more genes show

• dominance,

• recessiveness,

• sex linkage,

• phenotypes,

• genotypes

• and incomplete dominance

Complex Patterns of Heredity

• _ Characters usually display complex patterns of heredity, such as incomplete dominance, codominance, and multiple alleles.

• _

• Mutations can cause genetic disorders, such as sickle cell anemia, hemophilia, and Huntington’s disease.

• _ Genetic counseling can help patients concerned about a genetic disorder.

Section 3 vocabulary:

• 1. Genetic recombination 2. Polyploidy

Summary of genetics video

• http://www.bing.com/videos/search?q=genetic+videos&view=detail&mid=E7AEA272F3FDDB885163E7AEA272F3FDDB885163&first=0&FORM=LKVR19