Lecture 3 - Heredity Flashcards
What is variation?
Individuals differ in phenotype
What is heredity?
Offspring resemble their parents
What is competition?
There is differential reproductive success
What is competition?
There is differential reproductive success between individuals - some variation more advantageous than others
What did Mendel find in his pea breeding experiments?
One green parent, one yellow parent
in F1- generation 1 - all 4 peas were yellow
in F2 - 3 yellow and 1 green
What do Mendel’s findings suggest?
There must be 2 factors deciding on the colour (each parent)
There must be asymmetry (yellow more dominant that green)
What is A and a?
The two types of hereditary particle (alleles of a gene)
What is meant by homozygous?
Having two copies of the same allele
What is meant by heterozygous?
Having one copy each of two different alleles
What is a dominant gene?
Expressing its phenotypic effect when one or more copy is present
What is a recessive gene?
Expressing its phenotypic effect only shen two copies are present.
What is a punnett square?
Used if we know the genotypes of parents, then we can predict the probabilities of given genotypes and therefore phenotypes to the offspring
Are the probabilities of punnet squares equal/
yes - 25%
What happened when mendel added an allelic characteristic of smoothness to the green pea?
Predicted 1st generation all yellow
Predicted 3 yellow 1 smooth green for 2nd generation
Actually found:
- 1st generation all yellow
- 2nd generation some yellow, yellow smooth, some green, some smooth green - so combinations of phenotypes that never existed
What are the explanations for Mendel’s experiment of the smoothness of the pea?
There must be two different genes controlling colour and smoothness.
They must be on separate chromosomes and be passed on independently of one another.
What is the double punnett square?
Used in the case of there being 2 genes
So two genes A and B
Two alleles each, A a B b
How many possible genotypes are there in a double punnett square?
16 possible genotypes
How many possible phenotypes are there in a double punnet square?
4
What is the Hardy-Weinberg theorem?
Allele frequencies in a population remain constant unless one or more factors cause the frequencies to change.
It predicts frequencies of genotypes in a population.
What are the equations for the Hardy-Weinberg theorem?
p^2, 2pq and q^2 - all different ways we can calculate what proportion of individuals will have this phenotype
What is genetic drift?
Because populations are finite, allele frequencies therefore change by chance from generation to generation
What does genetic drift suggest about neutral alleles?
They even change in frequency over time, so populations can become dissimilar at the molecular level
What is genetic drift useful for?
Tracking evolutionary descent
Is genetic drift seen more in larger or smaller populations?
Smaller - can see more change in smaller populations
Quantitative genetics is based on
phenotypic correlations between relatives - allows us to infer how much variation in the phenotype we see is because of the genotype in relatives
Which type of twin show a more positive correlation in height?
Monozygotic twins - less strong for Dz as share less genes
What are the components of variation?
G or A: Variation due to genes
C: Variation due to shared environment
E: Variation due to unique or non-shared environment
What do Mz twins share?
All of the genetic influence and all of the shared environmental influence
What is the equation for the correlation of MZ?
corrMZ=G+Z
What do DZ twins share?
half genetic influence and all shared environment
What is the equation for the correlation of Dz twins?
corrDZ = 1/2G + C
If we take these correlation away from each other (corrMZ - corrDZ) what is showed?
1/2 G
can be flipped to find out G
G = 2 x (corrMZ - corrDZ)
two times the difference in correlation of the twins
- known as Falconer’s estimate of heritability
What is the meaning of h=1 and h=0 of heritability?
h=1 means - if height differs this is due to differences only in genotypes
h=0 means - if height differs this is due to differences only in the environment
Variation is measured between…
number between 0-1, which reflects the proportion of variation in the trait (height) in that population is due to variation in the genotype
