Biology 1202: MasteringBiology Chapter 23

Crossing over, resulting in an increase in genetic variation, occurs between _____.

Nonsister chromatids of homologous chromosomes. [This process produces chromosomes containing genes inherited from both parents.]

(Click on the diagram to start the animation.) This animation illustrates _____ as it occurs during _____.

crossing over ... prophase I. [Crossing over, the exchange of genetic material between the nonsister chromatids of homologous chromosomes, occurs during prophase I.]

Every few years a giant axe chops off the head of every person who is over 6 feet tall. How will this affect the human population?

Alleles that promote "tallness" will decrease in frequency. [A reduction in "tallness" alleles is the change expected as a result of this type of selection.]

(Click on the diagram to start the animation.) Which of these gametes contain one or more recombinant chromosomes?

B, C, F, and G. [These gametes carry chromosomes produced as a result of crossing over.]

The ease with which humans travel across the globe is likely to increase _____.

Gene flow. [When people travel or migrate, they take their alleles with them.]

A mutation occurs when _____.

There is a change in the DNA sequence of a gene [This is the definition of mutation.]

Genetic drift is a process based on _____.

The role of chance.

In human gamete production there is an average of _____ crossover events per chromosome pair.

2-3. [These crossover events increase the genetic variation among gametes.]

Which of these individuals is a homozygous genotype?

AA [When both of the alleles of a given gene pair are the same, the individual is homozygous for that gene.]

All the genes in a population are that population's _____.

Gene pool. [All the alleles of all the genes of a population make up a gene pool.]

Modern travel along with migration reduces the probability of _____ having an effect on the evolution of humans.

Genetic drift. [Modern travel and migration decreases the chances of there being a small, isolated population.]

Homologous pairs of chromosomes are lined up independently of other such pairs during _____.

Metaphase I.