Genetics and Evolution Flashcards

Which of the following best describes the law of independent assortment?

Answer: Genes on different chromosomes are inherited independently of one another

Mendel's law of independent assortment states that alleles of genes located on different (non-homologous) chromosomes segregate independently during gamete formation.

A woman who is a carrier for an X-linked recessive disorder mates with an unaffected man. What is the probability that their son will be affected?

Answer: 50%

A carrier mother (X^A X^a) passes either X^A or X^a to sons with equal probability; sons receiving X^a will be affected, giving a 50% chance.

Which type of mutation results in a premature stop codon?

Answer: Nonsense mutation

A nonsense mutation changes a codon that encodes an amino acid into a stop codon (UAA, UAG, or UGA), causing premature termination of translation.

In a testcross, an individual with an unknown genotype for a single trait is crossed with a:

Answer: Homozygous recessive individual

A testcross uses a homozygous recessive individual so that only the gametes of the unknown-genotype parent determine the offspring phenotype ratio.

Which of the following is an example of codominance?

Answer: AB blood type in humans expressing both A and B antigens

Codominance occurs when both alleles are fully and simultaneously expressed; AB blood type is the classic example because both A and B antigens appear on red blood cells.

Crossing over between homologous chromosomes occurs during which phase of meiosis?

Answer: Prophase I

Crossing over (recombination) occurs during Prophase I of meiosis when homologous chromosomes synapse and form the synaptonemal complex at chiasmata.

Which evolutionary mechanism causes allele frequencies to change randomly due to chance events in small populations?

Answer: Genetic drift

Genetic drift is the random fluctuation of allele frequencies due to chance, and its effects are most pronounced in small populations.