Mendel's Second Law

_Independent Assortment

Alleles for different traits separate independently. In a typical di-hybrid cross, the two genes are unrelated.

Mono-hybrid Cross 1 trait

Punnet square has 4 outcomes.

Di-hybrid Cross 2 traits

Punnet square has 16 outcomes.

Gametes get one allele from each gene, not both.

• Gametes are listed on the outside of the punnet square.

• RRyy × rrYY leads to gametes Ry, Ry, Ry, Ry × rY, rY, rY, rY.

Non-Mendelian Genetics

Epistasis

When one gene masks or modifies the effect of another gene.

• Happens if two or more genes are related or affect each other.

Gene A is epistatic to gene B means aa masks B_.

Genotype ratio is the same, phenotype ratio changes.

• For a AaBb × AaBb cross, phenotype ratio changes from 9:3:3:1 to 9:3:4

Lab Dog Color

The pigment gene is epistatic to the pigment color genes in yellow labs.
If the pigment gene is not expressed, none of the pigment color genes will have any effect.

Genetic Linkage

_Non-Mendelian

Genetic linkage influences inheritance.

A gene is considered linked to a chromosome if it exists on that chromosome.

There's a low chance that linked genes can become unlinked if crossing over occurs.
It is a higher chance if the genes are farther apart from each other on the same chromosome.

Autosome-Linked

Genes on the same chromosome are considered linked and are more likely to be inherited together.

• Not susceptible to independent assortment. Though meiotic recombination may split them up.

Y-Linked Only Males

Genes that are located on the Y-chromosome, influencing inheritance.

Women cannot have Y-Linked traits because they don't have the Y gene.

X-Linked

Genes that are located on the X-chromosome, influencing inheritance.

Red-Green Color Blindness - X-Linked Recessive

More common in males. He passes on his recessive copy to his daughters always.

X-Inaction Only Females

Females don't express twice as much X genes b/c they have twice as many X genes.

• One copy gets deactivated and becomes a barr body.

• This prevents double the dose of protein generation if both copies were active.

Tortoiseshell Cats

The color of their fur lives in the X-chromosome.
They have both copies of the gene and each copy gets turned off in different regions of the body.
They have both colors and either-or color gets deactivated in different regions of the body.