08 Genetics and Inheritance Free Online FlashCards

What does genetics study?

Genetics is the study of heredity and variation. Heredity concerns biological information passing from parents to offspring; variation explains differences among individuals.

Gene versus allele

A gene is a DNA segment contributing to a biological function or trait; an allele is an alternative DNA sequence of that gene.

Genotype versus phenotype

Genotype is an individual’s allele combination, such as Yy. Phenotype is the observable or measurable characteristic, such as yellow seeds.

What is Mendel’s law of segregation?

The law of segregation states that an individual’s two alleles for a gene separate during gamete formation, so each gamete receives one allele.

When does independent assortment apply?

For unlinked genes, alleles of different genes assort independently during gamete formation. An AaBb individual can produce AB, Ab, aB, and ab gametes.

Expected ratios for Yy × Yy

A Yy × Yy cross gives an expected genotype ratio of 1 YY : 2 Yy : 1 yy and, with complete dominance, a phenotype ratio of 3 yellow : 1 green.

What is the product rule?

The product rule multiplies probabilities for independent events: P(A and B) = P(A) × P(B).

When is the complement rule useful?

The complement rule subtracts the probability that an event does not occur from 1: P(at least one) = 1 − P(none).

Carrier probability for an unaffected child of two carriers

In an Aa × Aa cross, an unaffected child cannot be aa. Among the remaining genotypes AA and Aa, the conditional probability of being a carrier is 2/3.

What is a test cross?

A test cross mates an individual with a dominant phenotype, A_, to a homozygous recessive individual, aa, to determine whether the unknown individual is AA or Aa.

Core pedigree symbols

In a pedigree, a square represents a male, a circle a female, a shaded symbol an individual expressing the trait, and an unshaded symbol an individual not expressing it.

Clues for autosomal dominant inheritance

Autosomal dominant traits often appear in successive generations, affect males and females similarly, and can show father-to-son transmission.