phenotypes and quantitative genetics

lecture 1

what is a gene?

a unit of inheritance

what is an allele?

alternative form a single gene

what does it mean to be homozygous/homozygote

both alleles are the same

what does it mean to be heterozygous/heterozygote

having one copy of each allele

what is polygenic inheritance?

inheritance pattern where phenotypes are due to effects of multiple genes

what are quantitative traits?

traits that show continuous variation along a numeric or non-numeric scale and are influenced by multiple genes and environmental factors.

example: height, weight, length, haircolor

what are threshold traits?

traits with an underlying continuous distribution of alleles but only a few phenotypes

these traits have discrete continuous phenotypic variation, but they are quantitative.

-they are polygenic

-think of disease where you have it or don’t

-these traits are influenced by environment and can be expressed only after reaching a certain threshold of genetic and environmental factors.

what is an additive allele?

an allele that contributes equally to a phenotype (has a measurable value contributing to the phenotype)

-this happens when no one gene has a major effect

-if no environmental influences are present phenotypes can be predicted by adding up the quantitative value of each additive allele

what is heritability?

the proportion of phenotypic variance that is due to genetic factors in a given population in a specific environment It quantifies how much of the variation in a trait can be attributed to genetic differences among individuals.

-high heritability suggests that most phenotypic variance is b/c of genotype (genetic variation). Higher heritability is more likely to be strongly influenced by selection.

-low heritability would indicate that the variation is mostly due to environmental influences and that the trait is not effectively changed by selection.

what is concordance?

the proportion of twin pairs where both members have the same phenotype

what is discordance?

the proportion of twin pairs where the members of the pair have different phenotypes

what is a DIScontinuous trait?

a single-gene trait that allows differences to be assigned to discrete distinguishable categories

example: muscular hypertrophy in mice- they either have the condition or they don’t.

Discontinuous traits are black and white, you can make distinct categories

what are meristic traits?

traits that cause phenotypes to be recorded in whole numbers

example: number of seeds in a pod or number of eggs a chicken lays

what are continuous traits?

traits that exist along a spectrum i.e. aren’t black or white

for example: think of quantitative traits such as height, weight, and skin color.

These are traits that can exist between two extremes.

what is broad sense heritability

takes into account all the variations due to genetics

what is narrow sense heritability

estimates the amount of phenotypic variation due to additive variation