Genes and the environment Flashcards
what did Mendel find in his pea breeding experiment
- First generation - all yellow
- Second generation - one green and three yellow
define homozygous
two copies of same allele
define heterozygous
one copy of two different alleles
define dominant
always expressed in phenotype if present in genotype
what did Mendel find in the two gene case
independent segregation - different genes on different chromosomes that are independent of one another
define recessive
only expressed in phenotype if both present
What does the Hardy Weinberg theorem propose
Genotypes always appear in the frequency p2, 2pq and q2 (where p is the frequency of one allele and q is the other)= 1
what is Hardy Weinberg theorem dependent on
an infinitely large population and no natural selection
what is genetic drift
Because populations are finite, allele frequencies do in fact change (a little) by chance from generation to generation
Neutral alleles change in frequency over time even without natural selection
what is genetic drift useful for
tracking evolutionary descent
why is it difficult to establish which alleles are related
finding gene with minimal environmental input is difficult
what do phenotypic correlations have
a genetic component G plus a shared environment component C
what are used to show phenotypic correlations
twin studies show
what do twin studies show about phenotypic variability
The higher the heritability of the trait, the bigger the proportion of variation in phenotype that is explained by the genotype, then the bigger the difference between MZ and DZ correlations
what are the different 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 is heritability
what proportion of variation in the phenotype can be explained by variation in the genotype
Falconer’s estimate of heritability
corrMZ = G + C (100% shared genetics)
corrDZ = ½ G + C (50% shared genetics)
- corrMZ – corrDZ= ½ G
G = 2 * (corrMZ – corrDZ)
meaning of number in heritability
Number between 0 and 1 - reflects proportion of variation in that population due to variation in genotype
example of how heritability is not fixed
- Impoverished families - 60% of the variance in IQ is accounted for by the environment, and the contribution of genes is close to zero
Affluent families - almost exactly the reverse
Can we discover how genes and environment influence behaviour
in principle; it’s about mechanisms
However difficult to disentangle the genetic and environmental causes of behaviour
what is the cake analogy
-Individual ingredients of a cake cannot be distinguished in the final product, but we know they exist
-Similarly, the influences of genes and environment on behaviour are not always easy to discover, but they must exist
what does interaction mean
Genetic influence varies with the environment
what is the MAOA gene
on X chromosome -makes enzyme that metabolises neurotransmitters to recycle - genetic deficiencies
what results in flawed MAOA production
Faulty gene – no MAOA
Polymorphisms – variation in MAOA production
