8. Mechanisms of evolution Part 1

Question 1

Sources of variation in populations:

Answer 1

• Mutations
• Random pairing of gametes
• Genetic recombination
• Environmental factors

Question 2

What are mutations?

Answer 2

Any change in the arrangement or amount of DNA in a somatic cell or in a germ line cell.

Question 3

What is the effect of mutations in germ-line cells?

Answer 3

Mutations that occur in germ-line cells affect gametes and have the potential to be passed on to the next generation, and be incorporated in every cell of the offspring.

Question 4

What are mutagens? Give some examples:

Answer 4

Any influence that increases the rate of mutation.

Eg. High temperatures, chemicals (such as nicotine, radiation), (such as X-rays and UV light)

Question 5

What are point mutations?

Answer 5

Where a single nucleotide within the original DNA is affected.
-Single nucleotide polymorphisms (SNPs)

Question 6

What is a substitution mutation?

Answer 6

Involves the substitution of one base for another, which causes a change in only one codon.

Question 7

What is a synonymous/silent mutation?

Answer 7

Mutation which results in a codon that codes for the same amino acid (see no change except for the DNA sequence).
-Although the DNA has changed, the amino acids have not.

Question 8

What is a missense mutation and what is its effect on survival?

Answer 8

Mutation which results in a codon that codes for a different amino acid.
-Low-moderate effect on survival depending on the protein and location of change

Question 9

What is a nonsense mutation and what is its effect on survival?

Answer 9

Mutation which results in a codon that codes for a stop codon, therefore stopping translation.

• Increased changes to protein = increased effects
• Moderate-severe effect on survival depending on location

Question 10

What is a frameshift mutation? Describe its effect:

Answer 10

Addition/deletion of one or more bases displaces all other bases along one position, creating a whole new sequence of codons.
-A frameshift mutation almost always results in a non-functional protein (depends on where it occurs – at the end of protein may not have a large effect)

Question 11

What is a block mutation? Describe its effect:

Answer 11

Involves changes to segments of a chromosome, which can be seen in karyotypes
-Alternations to chromosomes can affect many genes simultaneously and result in severe effects on the phenotype

Question 12

List the 4 types of block mutations:

Answer 12

• Deletion
• Inversion
• Translocation
• Duplication

Question 13

What is deletion in relation to block mutation and what is its effect on survival?

Answer 13

Occurs when part of a chromosome is lost. The chromosome breaks in two places and re-joins, leaving a piece out.
-Moderate-severe effect on survival depending on the number of genes deleted and what they are

Question 14

What is inversion in relation to block mutation? Describe its effect:

Answer 14

Occur when part of a chromosome breaks off and re-joins the chromosome with the DNA ‘flipped’.
-The effects of this depend on where the breaks occur. If they occur in the coding region of a gene or in the promoter region, gene function is lost.

Question 15

What is translocation in relation to block mutation and what is its effect on survival?

Answer 15

Part of one chromosome breaks off and attaches to a different, non-homologous chromosome.
-Moderate-severe effect on survival as it results in gametes with extra or missing genes.

Question 16

What is duplication in relation to block mutation and what is its effect on survival?

Answer 16

Part of one chromosome is repeated and inserted into the same or another chromosome, resulting in duplicate segments.
-Moderate-severe effects on survival due to extra protein

Question 17

What do chromosomal abnormalities involve and when do they occur?

Answer 17

• Involve the loss or gain of whole chromosomes

- Such mutations arise due to non-disjunction of chromosomes during meiosis

Question 18

What is non-disjunction?

Answer 18

The failure of homologous chromosomes or chromatids to properly separate.

Question 19

What does aneuploidy refer to? Give an example:

Answer 19

The condition in which there is an addition or loss of a single chromosome from a cell.
-Changes the specific number of chromosomes
Eg. Down Syndrome

Question 20

What does polyploidy refer to? Give some examples:

Answer 20

An organism which has multiple sets of chromosomes.
-Changes the number of chromosome sets
Eg. Occurs in plants and a few rare non-vertebrates such as fish and brine shrimp

Question 21

What is population genetics?

Answer 21

The study of allele frequencies in populations and how they change over time in response to various evolutionary processes.

Question 22

What is a gene pool?

Answer 22

Total of the genetic information present in a population of organisms.

Question 23

What are polymorphisms and what does the word translate to?

Answer 23

Phenotypes that vary due to differences (more than one allele of a gene is present).
-‘Poly’ means multiple, ‘morph’ means form

Question 24

What is the frequency of polymorphic alleles affected by?

Answer 24

• Mutation- of an allele
• Immigration- of individuals into the population
• Emigration- of individuals out of the population
• Reproductive rate of individuals in the population

Question 25

What does gene flow refer to?

Answer 25

The transfer of alleles out of (emigration) or into (immigration) a population.

Question 26

What does genetic drift refer to? Give an example:

Answer 26

The change in allele frequencies over time due to random events.
-The smaller the population size, the greater the potential impact of genetic drift
Eg. In a small population of prey animals, more animals carrying a particular allele may be eaten than those with the alternative allele, as a result of chance.