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INHERITANCE…
This unit consists of 3 sub-topics…
VARIATION
WHAT IS INHERITANCE
GENETICS AND SOCIETY
SUB-TOPIC A… VARIATION.
WHAT IS A SPECIES ?
A Group of organisms which are very similar
AND Are able to produce
fertile offspring
The species is made up of different VARIETIES (breeds,ie Dogs )
All these are same species!Broccoli, kale, Cabbage, Sprouts
Cauliflower,are all members of the same species ! (Brassica Olearea)
Lemurs of Madagascar
Amazonian Frogs
Can you think of some more examples ? Write them down !!
…Interbreeding
Members of very different species cannot breed and produce offspring
For example,Dogs and Giraffes
…BUT (There’s always a ‘but’ in Biology) Sometimes the
members of two very similar species CAN interbreed.
HOWEVERAny offspring are
always STERILE
Eg. A Horse and a Donkey
…Make mine a MULE
What does ‘sterile’ mean ?
Try this one…
If a Horse…
Mates with a.. Zebra.
What is the result called ?
Can they have any babies ?
It’s a Zebrorse !!
So a species is ?
A group of organisms which can..
Interbreed AND……
Give birth to _________________
Fertile offspring
Write down some examples of SPECIES with their VARIETIES
VariationVariation can come about for two reasons:
1. Some features can be inherited. That means that you get them from your parents
2. Other features are affected by the environment.
3. Lots of features are a combination of both
Examples?
Environmental or Inherited?
How does variation come about?Sexual reproduction
Genetic information exchanged by
Characteristics
These are features you exhibit physically
( your looks)
Example: Eye colour
Traits
The different versions of a characteristic
Example: blue, green, and brown eyes
Why aren’t fruits from the same plant identical ?
What about this wheat grown in the same field from the same parent plants ?
Why does one organism look different to another ?
1. Do the members of this family have any similar features ?
2. Are the members different in any ways ?
3. What reasons can you think of to explain these differences ?
Inherited differences. These are due to
genes or the bits of message we get from a parents sperm and egg.
In plants the genes are in the pollen and ovule.
The genes are found in the nucleus of plant and animal cells.
Nucleus
Inherited Differences in Humans.
Genes control the characteristics that develop.
1/2 the instructions come from the father and 1/2 come from the mother.
The new individual is genetically unique.
So why are Identical twins not identical ? Twins have
identical genes in their bodies…….
Yet they do not have identical characteristics.
What do we find?
Height shows a continuous variation – there is a range of values with most people roughly in the middle
Eye colour, hair colour etc show a discontinuous variation – there are distinct groups but some are more common
Eye colour in 9K
0
1
2
3
4
5
6
7
8
blue green hazel brown grey black
Frequency
Discontinuous variation
•Cut and dried characteristics there are no in-betweens.
•Always caused by genes.
•Examples :- Natural hair colour, blood groups.
Discontinuous variation
0
1
2
3
4
5
6
7
8
9
10
Number of pupils
Tongue rollers Non -Tongue rollers
Graph to show number of girls who can roll their tongues.
Series1
Continuous Variation
•Gradual or not so clear-cut variation
•Bell shaped graph
•The classes are artificial and have been decided upon by us to make it easier to draw a graph.
•May be caused by genes or environment or both.
•Examples :- weight, leaf length, height, skin colour.
Continuous variation.
0
1
2
3
4
5
6
7
Number of students
6.5-7.0 7.0-7.5 7.5-8.0 8.0-8.5 8.5-9.0Length of index finger
Graph to show the length of girls index fingers in the class.
Class results
Inherited, environmental or both?
Example Cause Example Cause
Sex I Weight B
Height B Dyed blonde hair
E
Strength B Beard ICut on face
E Intelligence
B
Got a bad cold
E Blood group
I
Eye colour
I
Question 1 What is the term for an animal
that cannot breed A – Disappointed B – Fertile C – Sterile D – Hostile
Question 2
What do you get if you cross a horse with a donkey
A – Liger B - Zebrorse C – Binturong D - Mule
Question 3
Which of the following is an example of discontinuous variation
A – Finger print B - Height C – Weight D – Hand span
Question 4
What is an example of continuous variation
A – Tongue rolling B - Weight C – Finger print D – Blood group
Question 5
Which of the following is a group of living things that can interbreed to produce fertile offspring?
A - community B – population C – genus D - species
Question 6
Which of the following is a block graph of a characteristic showing continuous variation where the entire range of the characteristic is divided into smaller groups for convenience
A – Hysterectomy
B – Histogram
C – Hysterical
D – Bar chart
Question 7
Which of the following is a bell-shaped curve of a characteristic showing continuous variation where most individuals fall into the centre of the range?
A – Skewed distribution
B – Abnormal distribution
C – Normal distribution
D – Asymmetrical distribution
Question 8
What is the name of an animal resulting from a cross between a lion and a tiger
A – Tigron
B – Tigger
C – Puma
D – Sabre-toothed mouse
Now check your learning outcomes sheet.Make sure you have marked off ALL the boxes.Ask your teacher to go over any points you do not understand
SUB TOPIC B – WHAT IS INHERITANCE ?
Inheritance
Occurs when traits are passed down from parent to child.
These are things like eye colour, skin colour and hair colour.
They are inherited.
IDENTIFYING PHENOTYPES
– A description of the APPEARANCE of an organism
– A characteristic can have several phenotypes
Eg.A Daffodil can have yellow,white or orange flower colour
Patterns of Inheritance
The way in which inherited characteristics are passed on from parents to their offspring was first studied by an Austrian monk called Gregor Mendel.
He worked out patterns of inheritance by doing breeding experiments using pea plants
Genetics-’Monkey’ business
Modern genetics had its beginnings in an abbey garden, where a monk named Gregor Mendel documented a particular mechanism of inheritance.
He discovered the basic principles of heredity by breeding garden peas in carefully planned experiments.
His approach to science had been influenced at the University of Vienna by one of his professors: the physicist Doppler.
Mendel’s work...
In order to study inheritance, Mendel chose to use peas, probably as they are available in many varieties.
The use of plants also allowed strict control over the mating.
He chose to study only characters that varied in an ‘either-or’ rather than a ‘more-or-less’ manner.
Genetic crosses... To cross 2
varieties of pea plants, Mendel used an artist’s brush.
He transferred pollen from a true breeding white flower to the carpel of a true breeding purple flower.
Tracking heritable characteristics Mendel tracked
heritable characters for 3 generations.
When F1 hybrids were allowed to self-pollinate a 3:1 ratio of the 2 varieties occurred in the F2 generation.
Mendel’s law of segregation By carrying out these
monohybrid crosses, Mendel determined that their must be 2 forms of a gene for each character and that these segregate during gamete production.
Mendel discovered this c.1860.
DNA was not discovered until 1953.
Mendel’s impact
Mendel’s theories of inheritance, first discovered in garden peas, are equally valid for figs, flies, fish, birds and human beings.
Mendel’s impact endures, not only on genetics, but on all of science, as a case study of the power of hypothesis/deductive thinking.
Symbols and terminology... The symbol for parents is... The symbol for the offspring in the
first generation is... The symbol for the offspring of the
second generation is... The phenotype found most
frequently found through the generations is called the...
The less common phenotype is called
the...
Crosses involving only one characteristic are called MONOHYBRID CROSSES
p
f1
f2
DominantRecessive
TRUE BREEDING
If an organism is crossed with a member of the same strain
AND Offspring are
exactly the same kind
The organism is said to be TRUE BREEDINGThis means that offspring of true-breeding
white Guinea pigs are ALWAYS white
Monohybrid inheritance of coat colour in mice
Various coat colours are found amongst mice.Two of these are black fur and brown fur.
If a mouse has black fur, in this exerciseits phenotype will be represented:
If a mouse has brown fur, in this exercise its phenotype will be represented:
Consider the following cross.
true-breeding true-breeding black mouse x black mouse
Parents
F1 ?
Do you think the F1 will be all black offspring ? Do you think the F1 will be all brown offspring ? Do you think the F1 will be some black and some brown ?
1..You are right.
true-breeding true-breeding black mouse x black mouseParents
F1 all black offspring
A true-breeding black mouse crossedwith another true-breeding black mousecan only produce more black mice.
2 and 3…You are wrong.
true-breeding true-breeding black mouse x black mouse
Parents
F1
all black offspring
A true-breeding black mouse crossed with another true-breeding black mouse cannot produce brown mice,only black mice.
Consider the following cross.
true-breeding true-breeding brown mouse x brown mouse
Parents
F1?
1.Do you think the F1 will be all black offspring 2.Do you think the F1 will be all brown offspring 3.Do you think the F1 will be some black and some brown
2…You are right.
true-breeding true-breeding brown mouse x brown mouse
Parents
F1
all brown offspring
A true-breeding brown mouse crossedwith another true-breeding brown mouse can only produce more brown mice.
1 and 3…You are wrong.
true-breeding true-breeding brown mouse x brown mouse
Parents
F1all brown offspring
A true-breeding brown mouse crossed with another true-breeding brown mouse cannot produce black mice, only brown mice.
Consider the following cross.
true-breeding true-breeding black mouse x brown mouseParents
F1 ?1.Do you think the F1 will be all black offspring 2.Do you think the F1 will be all brown offspring 3.Do you think the F1 will be some black and some brown
1…You are right.
true-breeding true-breeding black mouse x brown mouseParents
F1all black offspring
The genetic information for black coat colourmasks the genetic information for brown coat colour.The black colour is dominant and the brown colour is recessive.
2 and 3…You are wrong.
true-breeding true-breeding black mouse x brown mouse
Parents
F1all black offspring
The genetic informationfor black coat colour that comes from oneparent dominates andmasks the genetic information for brown coat colour that comesfrom the other parent.So all the F1 mice inthis cross are black.
How is this information carried then ? On thread-like
structures called CHROMOSOMES
Found in the______________Of every cell Two matching sets of
23 arranged in pairs46 in total (in Humans)A picture of them is
called a KARYOTYPE
nucleus
..So what’s the difference between Males and Female chromosomes then ?
..SEX CHROMOSOMES
There are TWO X and Y They are the
23rd pair Have a look to
see who has what XX XY
Have a look at the next slide.Identify the gender of the four individuals from their Karyotypes
Meiosis
Cell division – ‘reduction division’ (different from Mitosis)Production of sex cells called gametes containing HALF the normal number of chromosomes (HAPLOID)
Why do we need Meiosis?
Meiosis is necessary to halve the number of chromosomes going into the sex cells
Why halve the chromosomes in gametes?
At fertilisation the male and female sex cells will provide ½ of the chromosomes each – so the offspring inherits characteristics from BOTH parents
When a sperm and egg cell(Gametes) fuse together, they produce this. The fullchromosome number is restored (46 or
DIPLOID)
We use this word to describe cells which contain the full
complement of genetic material. In humans this would be
46 chromosomes (23 pairs)
Division of a cell to produce 2 daughter cells which each has the same
number and kind of chromosomes as the mother cell
Type of reproduction that involves fusion of gametes containing the HAPLOID
(HALF) number of chromosomes.
Why is this important ?
X YX X
X X YX
XX XY XX XY
female male female male
Parents
Sex cells
Offspring
50% of the offspring should be male and 50% should be female, eg a ratio of 1:1.
female male
Determination of gender:
Genes Bits of information passed down from parent to child.Carried on the Chromosomes which are made of DNA
Each Gene has two forms called ALLELES one from each parent
The set of genes an organism possesses is called its GENOTYPE
Gene control of characteristics All characteristics are controlled
by a minimum of 2 genes.
These genes give the characteristic a different of presenting itself.
Different genes that control the same feature are called ALLELES
EYE COLOUR
Possible alleles – blue , brown, green, hazel etc (each colour needs its own gene)
It is possible to have pairs of different alleles, alleles are usually given a letter
REMEMBER…Genotype and phenotype Genotype is the letter or term
used to describe the allele of an individual gene or pair of genes
Phenotype – is how the gene (or pair) shows itself, how it appears.
Dominance and recessive- ness
Some alleles for a feature are able to mask the influence of other (weaker) gene when they are paired
Stronger gene is DOMINANT and is represented by a capital letter e.g. H
The masked gene is RESSESIVE shown as lower case of the same letter e.g. h
Gene diagram – Flower colour
Genotype of alleles- R = red flower
r = yellow flower
All genes occur in pairs – so 2 alleles affect a characteristic – possible combinations are;
genotype RR Rr rrPhenotype RED RED YELLOW
Gene diagram – Flower colour
Male female
RR rr
parent
gamete R R r r
Offspring genotype Rr RrRrRr
Phenotype All red
Gene diagram – Flower colour
Male female
Rr Rr
parent
gamete R r R r
Offspring genotype RR RrRrrr
PhenotypeRed yellow red red 3 red : 1 yellow
Gene diagram – Flower colour
Male female
Rr rr
parent
gamete R r r r
Offspring genotype Rr Rrrrrr
PhenotypeRed yellow yellow red
Red 50% yellow 50%
Punnett Square
Another method of showing crosses
Gamete genotypes are inserted
Parent genotypes are inserted B=black b=white
Bb male black
bb white female
B b
b
b
What are the crosses
Bb bb
Bb bb
2 white and 2 black offspring
50:50 chance with these parents
Ok… Lets look at it again
Alleles… Usually represented by letters. T –Capital form
is considered a dominant allele
t – Lower-case form is considered a recessive allele
TT – shows the dominant phenotype
Tt or tT – is also dominant
tt - shows the recessive phenotype
Punnett Square..if T is the allele for being ‘Tall’
Uses mum and dad’s GENOTYPES to determine the possible traits of their offspring.
4 offspring each with the genotype Tt
Tt Tt
Tt Tt
T T
t
t
What is the phenotype of the 4 offspring ?
Monohybrid inheritanceLet the allele for round seeds be: R (dominant
allele)Let the allele for wrinkled seeds be: r (recessive allele)
Parents phenotype round seeds x wrinkled seedsgenotype RR rr
Gametes
F1 generation
R R r r
F1 phenotypes 100% plants producing round seeds
F1 genotypes 100% heterozygotes Rr
gametes R Rr Rr Rrr Rr Rr
gametes
F1 cross
Parents phenotype round seeds x round seeds genotype Rr Rr
Gametes
F2 generation
R r rR
Phenotype 75% plants producing round seeds
25% plants producing wrinkled seeds
Genotype 25% RR 50% Rr 25% rr
Ratio 3:1 Round seeds: wrinkled seeds
gametesgametes R rR RR Rrr Rr rr
Does the observed ratio match the theoretical ratio?
The theoretical or expected ratio of plants producing round or wrinkled seeds is 3 round :1 wrinkled
Mendel’s observed ratio was 2.96:1 The discrepancy is due to statistical error The observed ratio is very rarely the
same as the expected ratio The larger the sample the more nearly
the results approximate to the theoretical ratio
Harry Potter and the recessive allele
How Are Wizards Made?
How Are Wizards Made?
Being a wizard or a muggle is all decided by genetics
All humans including wizards receive one allele from each parent
How Are Wizards Made?
The allele for wizarding
ability is m
Wizards have the alleles mm
How Are Wizards Made?The allele for Muggleness is M
Muggles have the alleles Mm or
MM
M is dominant to m so you can only be a wizard if you have no M allele
The Malfoys
Lucius Malfoy (mm)
Narcissa Malfoy (mm)
Draco Malfoy( )
The Malfoys are a ‘pure blood’ family
All their ancestors are wizards so they must have the alleles mm
mm
Lily Potter (mm)
James Potter (mm)
Harry Potter (WW)
Both Harry’s parents had magical ability so they must both have been mm
They passed these alleles on to Harry
The Potters
mm
The Weasleys are pure blood wizards so they all have the alleles mm
Hermione is a powerful witch so she must be mm
Both her parents are muggles so they must be Mm so they can give her a m allele each
Mm Mm
mm
Tom Riddle is a ‘half blood’.
His mother was a witch (mm) and his father was a muggle
His father must have had the alleles Mm so he could give him the other m allele
mm Mm
mm
Filch is a ‘squib’
Both his parents are mm so he should be too because he can’t get an M allele from either parent but he can’t do any magic
This means he has a mutation so his wizarding powers don’t work or the man he thinks is his father isn’t really and his mother had an affair with a muggle!
What wizarding alleles would Ron and Hermione’s children have?
Ron (mm)
Hermione (mm)
Children
( )mm
Ron
m m
Hermione
m
m
Their children could only get the m allele from both parents so they would all be wizards
mm mm
mm mm
What wizarding alleles would Ginny and Dudley’s children
have? If Dudley is Mm
Ginny mm
Dudley Mm
Children
WW or mMmM mm
Dudley
m M
Ginny
m
m
Half of their children would be likely to get the m allele from both parents so they would be wizards
The other half would be likely to get an M allele from Dudley and would be muggles
m m
m m
m M
m M
What wizarding alleles would Ginny and Dudley’s children have?
If Dudley is MM
Ginny mm
Dudley MM
Children
WMm M
Dudley
M M
Ginnym WM WM
m WM WM
Their children would get the m allele from Ginny and the M allele from Dudley so they would all be muggles
m M m M
m M m M
What wizarding alleles would
You expect Hermione’s
brothers and sisters
to have ?
Mr Granger
m M
Mrs Grange
r
m WW WM
M WM MM
The Granger’s children have a one in four chance of getting m alleles from both parents and having magical ability
They also have a one in four chance of getting M alleles from both parents and being a muggle
They could also get only one m from their mother or father and still be a muggle
m M
m M
m m
M M
Now check your fact sheet.Make sure you have marked off ALL the boxes.Ask your teacher to go over any points you do not understand
SUB-TOPIC C
GENETICS AND SOCIETY
SELECTIVE BREEDING
Look at the difference between these species of dog :
Wild dogs Terriers
Collies Viemerana
What were the differences between the dogs?
•Size
•Colour
•Muscle development
•Length of coat
•Job
•Nature
Where have all these different species come from?
All these species are related to the wolf. But how?
Over thousands of years man has selected characteristics in dogs that are useful…..
•Very small dogs•Used for pets
•Large hunting dogs•Strong & powerful
•Large working dogs•Strong and athletic
Selective Breeding is the gradual improvement of animal and plant
characteristics over time, for man’s benefit.
Select for breeding only those animals or plants with desirable characteristics
This artificial selection of characteristics happens in plants
as well..
In the wild there are various species of corn plant
Good point: Strong stem
Bad point: Small head
Good point: Huge head of grain
Bad point: Drought sensitive
1
2
3
4
Bad point: Small root
Good point: strong roots
Bad point: Small plant
Good point: Disease resistant
Good point: Strong stem
Good point: Huge head of grain
Super CORN!
Good point: Strong roots
Good point: Disease resistant
Look what has happened to the varieties of the corn over last few hundred years.
Look at the variety of plants that have been artificially selected from mustard!
Growing lots of different varieties of wheat…………
……looking for new characteristics.
Things I must know about selective breeding(SB)
is the gradual improvement of organisms characteristics – for humans benefit.
takes hundreds of years
We have lots of SB animals and plants
SB animals & plants produced higher yields:
1. more milk2. more meat3. more fruit
MUTATIONSA mutation is a change
in the structure and amount of an
organism’s genetic material
How can mutations lead to big changes? Accumulation of many small
mutations, each with a small effect
Accumulation of several small mutations, each with a large effect
One large mutation with a large effect
Normal fly head
This is a normal Fly’s head
Antennapedia fly
Here,the legs replace the antennae on the head…a harmful mutation
What about Mutation ?
Spontaneous(very rare !) Increases caused by
environmental factors(‘Mutagens’)
UV light X-rays Benzene, formaldehyde, carbon
tetrachloride,colchicines.
Mutagens and their effects
Ionising radiation – Nuclear radiation, xrays, gamma rays (e.g. medical treatment) associated with development of cancers (e.g. leukaemia, thyroid cancer and skin cancer
Mutagens and their effects
Viruses and microorganisms – integrate into human chromosome, upset genes and can trigger cancer
Mutagens and their effects
Environmental poisons – Organic solvents such as formaldehyde, tobacco, coal tars, benzene, asbestos, some dyes
Mutagens and their effects
Alcohol and diet – High alcohol intake increase the risk of some cancers. Diet high in fat and those containing burned or highly preserved meat
Harmful mutations
Cystic fibrosis and sickle cell anaemia
Dysfunctional proteins Albinism – caused by mutation
in gene of enzyme pathway of melanin
More harmful mutations Bacteria – antibiotic
resistance through mutation, transfer between bacterial species
Super bugs such as MRSA have arisen this way
RNA viruses – such as HIV – mutates it’s protein coat so that the host human is unable to make antibodies quick enough against it
Down’s Syndrome is the most common chromosomal abnormality.
It occurs in 1:800 to 1000 live births.
Look at the following example of a harmful mutation….
Cause
92% to 95% of all causes of Down’s Syndrome are attributable to an extra chromosome 21.
Children with an extra chromosome 21 are born to parents of all ages but greater risk for women 35 years and older.
Intelligence
This varies from severely retarded to low normal intelligence but is generally within the moderate range.
Social Development
May be 2 to 3 years beyond the mental age, especially during early childhood.
Sensory Problems
Strabismus, Myopia ,Hyperopia, excessive tears, head tilt, cataracts.
Physical Disorders
-Respiratory infections.
Leukemia (is 10 to 30 times more frequent). Thyroid dysfunction.
How can we tell if a baby will have Down’s Syndrome ?
..Amniocentesis testing
Fluid is drawn from the womb
It’s Amniotic fluid
It contains cells from the foetus
These can be used to give a ‘Karyotype’Remember…this gives a picture of the
chromosomes of an organism………..
Does this baby have Down’s..?