Genetics Exam 2 (Lecture Slides)

What is probability in genetics?

It expresses the likelihood of an event, ranging from 0 to 1; Mendelian ratios are probabilities.

What are independent events?

Events where the outcome of one does not affect the other, e.g., coin toss or sex of children.

What law calculates probability of two independent events?

The product law (multiplication rule): P(A and B) = P(A) x P(B).

What law calculates probability of mutually exclusive events?

The sum law (addition rule): P(A or B) = P(A) + P(B).

What is conditional probability?

The probability of a specific outcome given that another outcome has occurred.

What is the Binomial Theorem used for in genetics?

To calculate outcomes of repeated trials with two outcomes, such as dominant vs recessive traits.

What is the null hypothesis in genetics?

It assumes no difference between observed and expected outcomes; deviations are due to chance.

What statistical test is used to evaluate the null hypothesis in genetics?

Chi-square (x²) test, which compares observed and expected values.

When do we reject the null hypothesis?

When p < 0.05, meaning the difference is unlikely due to chance.

What is a pedigree analysis?

A method to track inheritance of traits across generations using standardized symbols.

What do shaded symbols represent in pedigrees?

Individuals expressing the trait of interest.

What is a proband?

The first individual identified with a trait in a pedigree study.

What is an allele?

An alternative form of a gene; mutations are the source of alleles.

What is the wild-type allele?

The most frequent allele in nature, usually (but not always) dominant.

What happens if neither allele is dominant?

Incomplete dominance or codominance occurs; phenotype ratios equal genotype ratios.

What is incomplete dominance?

Heterozygotes display an intermediate phenotype, e.g., red x white flowers = pink.

What is codominance?

Heterozygotes express both alleles simultaneously, e.g., roan cattle or AB blood type.

What are multiple alleles?

More than two alleles exist for a gene; classic example is ABO blood group.

Which alleles are codominant in ABO blood group?

IA and IB are codominant; both dominant to IO.

What are lethal alleles?

Alleles that cause death when homozygous (recessive lethal) or even in heterozygotes (dominant lethal).

Give an example of a dominant lethal allele in humans.

Huntington’s disease.

What is gene interaction?

When multiple genes contribute to a phenotype; includes epistasis and complementation.

What is recessive epistasis?

Homozygous recessive alleles at one locus mask expression at another locus, e.g., coat color in mice.

What is dominant epistasis?

A dominant allele at one locus masks expression at another locus, e.g., white color in summer squash.

What is complementation?

Two different recessive mutations in different genes can restore wild-type phenotype when combined.

What is a complementation test?

A cross of two mutants to determine if mutations are in the same or different genes.

What are sex-linked traits?

Traits controlled by genes on sex chromosomes; inheritance differs between males and females.

What is the criss-cross pattern of inheritance?

X-linked traits pass from mother to son and father to daughter.

What is sex-limited inheritance?

Phenotypes expressed only in one sex, regardless of genotype in the other.

What is sex-influenced inheritance?

Phenotypes where expression differs between sexes, e.g., male baldness.