lecture 3 - heredity Flashcards
what is heredity?
offspring who resemble their parents - how is the phenotype determined?
what did Mendel do?
Breeded pea plants – looked at the colour of pea pods – interbreeded plants of a single colour together – yellow or green pea pods
what did Mendel expect to find?
when bred two of the same generation together they should be the same colour pods
what did Mendel actually find?
when bred yellow with green pea pods all of them had yellow pea pods – for f2 – when he bred them together – ¾ had yellow pea pods and ¼ had green pea pods
why were Mendels experiments important?
tells us 2 important things about hereditary – there has to be 2 of what is passed from one to the next and you get one, and there has to be some asymmetry – what makes you yellow is stronger than what makes you green
how is your phenotype determined?
No matter what allele went forward you still have one of each as you inherit one from each parent
what does homozygous mean?
Having two copies of the same allele
what does heterozygous mean?
Having one copy each of two different alleles
what does a dominant allele mean?
Expressing its phenotypic effect when one or more copy is present
- A
what is a recessive allele?
Expressing its phenotypic effect only when two copies are present - a
- like the green pea pod, need two of the green for it to happen
what did Mendel experiment in his two-gene case?
he breeded yellow smooth pea pods and green wrinkly pea pods for first gen - all smooth yellow
2nd gen - 75% expected to have smooth yellow
What found – gen 1 all smooth yellow, gen 2 – 56% smooth yellow, 19% yellow wrinkly, 19% smooth green and 6% wrinkly green – seeing combos that have never been seen before
what is the importance of Mendels two-gene case?
has to show there are separate things which cause the colour and wrinkliness and this is passed on independently – has to be on diff chromosomes
what is the Hardy-Weinberg theorem?
Work out the frequency of diff phenotypes AA = 0.1 x 0.1 , prob of getting Aa = 0.1 x 0.9 , Aa = 0.1 x 0.9, aa = 0.9 x 0.9
Have to add up to one
Express algebraically – A = P, a = q
AA= p x p = P^2 , Aa = p x q = pq, Aa = p x q = pq, aa = q x q = q^2
Dominant trait = p^2 , homozygous recessive = q^2, prob of being heterozygous = 2pq – 2 diff ways to how you can be pq
what is genetic drift?
allele frequencies do in fact change (a little) by chance from generation to generation, it is more obvious in smaller populations
E.g. if you toss a coin four times, you won’t always get two heads and two tails
what do neutral alleles mean?
they are equally beneficial
how are traits determined?
polygenic - many genes
what are quantitative genetics?
analyses how traits pass to offspring w/o knowing which is responsible for it
why do we compare between relatives?
to see if a trait is heritable - if there is there will be a pos correlation, to see what is due to environment and genes
what else do we use to determine correlations between relatives?
twin studies
what are the components of variation?
genes, shared environment or a unique/non-shared environment e.g. one may break arm/ have psych trauma
how do we work out heritability?
correlation of MZ – correlation of DZ = ½ G
G =2 x (correlation MZ – correlation DZ)
what does a heritability of 1 mean?
all the variation in phenotype is explained by variation in genotype in that pop – can vary amongst pops
what does a heritability of 0 mean?
If it is 0 none of the variation of phenotype is explained by variation in genotype in that pop
