Chapter 23: The evolution of populations (1)

Question 1

Define microevolution.

Answer 1

Evolution on its smallest scale is called microevolution. It is defined as the change in allele frequencies in a population over generations

Question 2

What are the 3 mechanisms that can cause allele frequency change/microevolution?

Answer 2

1. Natural selection
2. Genetic drift (chance events that alter allele frequencies)
3. Gene flow (the transfer of alleles between populations).

Question 3

Only natural selection consistently improves the match between organisms and their environment. True or false?

Answer 3

True. Only natural selection consistently improves the match between organisms and their environment.

Question 4

Define genetic variation.

Answer 4

Genetic variation is defined as differences among individuals in the composition of their genes or other DNA sequences.

Question 5

How are genetic variations created?

Answer 5

Genetic variation among individuals is caused by differences in:

– genes or
– other DNA segments

Question 6

Variation results from _____________on a single phenotypic character.

Answer 6

Variation results from the influence of multiple genes (two or more genes) on a single phenotypic character.

Question 7

Only a small percentage of nucleotide variation results in phenotypic variation. Why?

Answer 7

Many nucleotide variations occur within introns, noncoding segments of DNA lying between exons, the regions retained in mRNA after RNA processing.

Question 8

All phenotypic variation result from genetic differences. True or false?

Answer 8

False. Phenotype is the product of an inherited genotype and many environmental influences.

Question 9

How can genetic variation be measured?

Answer 9

Genetic variation can be measured as:

– gene variability or
– nucleotide variability

Question 10

How do new alleles arise?

Answer 10

New alleles can arise by mutation, a change in the nucleotide sequence of an organism’s DNA, or gene duplication.

Question 11

What results from point mutations in non-coding regions?

Answer 11

Point mutations in these noncoding regions generally result in neutral variation, differences in DNA sequence that do not confer a selective advantage or disadvantage.

Question 12

______can result in genetic variation by recombining existing alleles.

Answer 12

Sexual reproduction can result in genetic variation by recombining existing allele.

Question 13

What is genetic code redundancy?

Answer 13

Genetic redundancy means that two or more genes are performing the same function and that the inactivation of one of these genes has little or no effect on the biological phenotype.

Question 14

Sexual reproduction shuffles existing alleles. What are the 3 mechanisms that contribute to this shuffling?

Answer 14

Three mechanisms contribute to this shuffling: crossing over, independent assortment of chromosomes, and fertilization

Question 15

Define genotype.

Answer 15

An individual’s combination of alleles is known as their genotype.

The different types of genotypes are- homozygous recessive (pp), homozygous dominant (PP), and heterozygous (Pp).

Question 16

define allele.

Answer 16

One of two or more versions of a genetic sequence at a particular region on a chromosome.

An individual inherits two alleles for each gene, one from each parent

Question 17

Define allele frequency.

Answer 17

Allele frequency refers to how common an allele is in a population.

Question 18

What does it mean when a locus is fixed?

Answer 18

A locus is fixed if all individuals in a population are homozygous for the same allele.

Question 19

How can the frequency of an allele be calculated for a diploid organism?

Answer 19

For diploid organisms, the total number of alleles at a locus is the total number of individuals times 2.

Question 20

How can one calculate the number of dominant alleles on a locus?

Answer 20

The total number of dominant alleles at a locus is:

• 2 alleles for homozygous dominant individual
• plus 1 allele for each heterozygous individual;
  – The same logic applies for recessive alleles