Genetic Diversity

Question 1

What is a mutation?

Answer 1

An alteration to the DNA base sequence. Often arise spontaneously during DNA replication.

Question 2

Why might a mutation not lead to change in the amino acid sequence?

Answer 2

• genetic code is degenerate so mutation may end up coding for same amino acid as the original triplet.
• mutation may occur in intron

Question 3

What is a substitution mutation?

Answer 3

When a nucleotide in the DNA sequence is replaced by another. This is more likely to be a quiet mutation, meaning no change occurs in the amino acid sequence.

Question 4

What is a deletion mutation?

Answer 4

When a nucleotide in the DNA sequence is lost. This is more likely to be harmful and significant as it leads to a frame shift which means the entire amino acid sequence will be different.

Question 5

What is a mutagenic agent? Give examples of this.

Answer 5

Factors that increase the rate of gene mutation. X-rays, UV light, gamma rays, certain chemicals e.g. in alcohol and tobacco.

Question 6

What is a polyploidy chromosome mutation?

Answer 6

Where an individual has three or more sets of chromosomes instead of two.

Question 7

What is chromosome non-disjunction?

Answer 7

When chromosomes fail to separate correctly in meiosis, resulting in gametes with one or more less chromosomes than normal.

Question 8

What is meiosis?

Answer 8

A form of cell division that produces four genetically different haploid cells known as gametes.

Question 9

What is meiosis?

Answer 9

A form of cell division that produces four genetically different haploid cells known as gametes.

Question 10

How does meiosis differ from mitosis?

Answer 10

• meiosis produces four genetically different cells with half the number of chromosomes as the parent cells
• mitosis produces two genetically identical cells with the same number of chromosomes as the parent cells.

Question 11

What happens during meiosis I?

Answer 11

1. Homologous chromosomes pair to form bivalents.
2. Crossing over occurs at chiasmata.
3. Cell divides into two. Homologous chromosomes separate randomly. Each cell contains either maternal or paternal copy.

Question 12

What happens during meiosis II?

Answer 12

1. Independent segregation of sister chromatids.
2. Each cell divides again, producing 4 haploid cells.

Question 13

In which two ways does meiosis produce genetic variation?

Answer 13

1. Crossing over during meiosis I
2. Independent assortment of homologous chromosomes and sister chromatids.

Question 14

Define population.

Answer 14

All the organisms of a particular species that live in the same place.

Question 15

What is an allele?

Answer 15

Different forms of a particular gene, found at the same locus on a chromosome. A single gene could have many alleles.

Question 16

Define genetic diversity.

Answer 16

The total number of different alleles in a population.

Question 17

What advantage does a high genetic diversity provide?

Answer 17

Ability to adapt to a change in environment; allows natural selection to occur.

Question 18

Explain how natural selection results in development of new characteristics.

Answer 18

• random mutations result in new alleles.
• some alleles provide an advantage, making an individual more likely to survive and reproduce.
• their offspring receive the new allele, and frequency continues to increase over many generations.

Question 19

What is directional selection?

Answer 19

Occurs when environmental conditions change. Individuals with phenotypes suited to the new conditions will survive and pass on their genes. Over time the mean of the population will move towards these characteristics.

Question 20

Give an example of directional selection.

Answer 20

Antibiotic resistance. Bacteria with a mutation allowing them to survive in the presence of antibiotics will reproduce. Therefore frequency of this allele will increase and the population will shift to have greater antibiotic resistance.

Question 21

What is stabilising selection?

Answer 21

Occurs when environmental conditions stay the same. Individuals closest to the mean are favoured, and any new characteristics are selected against. Results in low diversity.

Question 22

Give an example of stabilising selection.

Answer 22

Birth weight; babies that weigh around 3kg are more likely to survive than those at lower or higher weights.

Question 23

Define a niche.

Answer 23

The role of a species within its environment. Species sharing the same niche will compete with each other.

Question 24

What are the three types of adaptation? Give examples of each.

Answer 24

• anatomical e.g. oily fur
• physiological e.g. venom production
• behavioural e.g. hibernation