Sex-Linkage & Complex Traits

Chromosome Theory of Heredity

Genes are located in chromosomes

X and Y chromosomes

sex chromosomes (non-identical but share some genes)

Example of X-linked inheritance

Hemophilia

Who is the heterogametic sex?

Males

Females produce only _-bearing gametes

X

Multifactorial traits are determined by multiple ___ and ___ factors acting together.

genetic and environmental

Multifactorial is also called…

complex traits, quantitative traits

Complex traits

traits that vary in the population

Genetic architecture of a complex trait

specific effects and combined interactions of all genetic and environmental factors

Quantitative traits

phenotypes differ in quantity rather than type (such as height)

segregation and recombination

In a genetically heterogeneous population, genotypes are formed by ____ and _____

inbred

Variation in genotype can be eliminated by studying _ lines that are homozygous for most genes

Variation in genotype can be eliminated by studying F1 progeny of inbred lines that are…

uniformly heterozygous

Continuous traits

continuous gradation from one phenotype to the next (height)

Categorical traits

phenotype is determined by counting (hen’s eggs)

Threshold traits

only two, or a few phenotypic classes, but their inheritance is determined by multiple genes and environment (adult-onset diabetes)

Distribution of a trait in a population

proportion of individuals that have each of the possible phenotypes

Mean

peak of distribution

Variance

spread of distribution estimated by squared deviation from the mean

Standard deviation

square root of the variance

Normal distribution

symmetrical curve produced by data in which half points are above and half points are below mean

What does the distribution of a trait in a population imply about its inheritance?

nothing

Variation of a trait can be separated into ____ and ____ components.

genetic and environmental

Genotypic variance

variation in phenotype caused by differences in genotype

Environmental variance

variation in phenotype caused by environment

Total variance

combined effects of genotypic and environmental variance

Broad-sense heritability (H2) includes…

all genetic effects combined

Identical twins

arise from the splitting of a single fertilized egg = genetically identical

Fraternal twins

arise from two fertilized eggs = siblings

Liability

quantitative trait that presents a genetic risk for a threshold trait

What is an example of a common multifactorial disorder in human families?

heart disease; Genetic risk = family history, Environmental risk = overweight and smoking