Lecture 30- Mendelian genetics

What makes chromosomes “linked”?

If genes are really close on a chromosome

If genes did not assort independently during gamete formation, what would be the phenotypic ratio expected in the progeny in a dihybrid cross?

3:1

How do we determine the probability of 2 or more independent events will occur together in some specific combination?

Multiplication rule

How do we determine the probability of 2 or more mutually exclusive events will occur together in some specific combination?

Addition rule

When is it better to use probability instead of punnets squares?

For trihybrid crosses or more complicated ones

When do homologous chromosomes assort independently ?

During metaphase I in meiosis

Incomplete dominance

Phenotype is a blend of both in heterozygotes

Complete dominance

Phenotype is dominant in heterozygotes

Co dominance

Results in the heterozygotes having a unique phenotype that is different from the homozygous phenotypes

How is blood type determined?

By carbohydrate patterns displayed on red blood cell proteins

What differentiates between independent assortment and segregation?

The law of independent assortment requires describing two or or genes relative to one another

Pleiotropy

Occurs when one gene (or the alleles of one gene) affect multiple phenotypes

Penetrance

If a homozygous genotype doesn’t always produce a specific phenotype in all members of the group (phenotype is usually “either-or”

Expressivity

When in a group of individuals with the genotype for a specific gene, a range of traits is displayed

Epistasis

Where the phenotypic expression of a gene at one locus affects the phenotypic expression at a second locus

Complete penetrance

Identical known genotypes yield 100% expected phenotype

Incomplete penetrance

Identical known genotypes yield <100% expected phenotype

Constant expressivity

Identical known genotypes with no expressivity effect yield 100% expected phenotype

Variable expressivity

Identical known genotypes with an expressivity effect yield a range of phenotypes

Incomplete penetrance with variable expressivity

Identical known genotypes produce a broad range of phenotypes due to varying degrees of gene activation and expression

Multifactorial

Phenotype can depend on genotype and environment ex/ hydrangeas with different soils can grow different coloured flowers