2 Inheritance Patterns and Genetic Analysis Free Online FlashCards

What are alleles?

Alleles are different forms of a gene.

How do genotype and phenotype differ?

Genotype is an individual's allele combination; phenotype is the observable trait.

What does Mendel’s law of segregation state?

The two alleles for a gene separate during gamete formation, so each gamete receives one allele.

When does independent assortment apply?

Alleles of different unlinked genes assort independently into gametes. Nearby genes on the same chromosome may be inherited together.

What is complete dominance?

In complete dominance, a heterozygote shows the dominant phenotype; the recessive phenotype appears only in a recessive homozygote.

What does a Punnett square show?

It combines possible parental gametes to show possible offspring genotypes. The outcomes are probabilities for each conception, not guaranteed counts.

What ratios are expected from $Yy \times Yy$?

The expected genotype ratio is $1\,YY:2\,Yy:1\,yy$; with complete dominance, the phenotype ratio is $3:1$.

How does a test cross reveal an unknown genotype?

Cross the individual with a homozygous recessive individual. Recessive-phenotype offspring show that the unknown parent carried a recessive allele.

What phenotype ratio is expected in an independently assorting dihybrid cross?

With complete dominance and independent assortment, $AaBb \times AaBb$ gives an expected phenotype ratio of $9:3:3:1$.

What do the symbols in a pedigree conventionally represent?

A pedigree traces a trait across generations. Squares conventionally represent males, circles females, and shaded symbols individuals with the trait.

What is the chance of an affected child when both parents carry an autosomal recessive allele?

For two carrier parents, $Aa \times Aa$, each child has a $\frac{1}{4}$ chance of being $aa$ and affected, assuming complete penetrance.

Why is there no father-to-son transmission of an X-linked allele?

An X-linked allele is not passed from father to son: a father gives his X chromosome to his daughters, not his sons.