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 mutations may end up coding for the same amino acid as the original triplet

Mutation may occur in an 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 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 more or less chromosome than normal

Question 8

What is meiosis?

Answer 8

A form of cell division that produces four genetically different haploid cells (cells with half the number of chromosomes found in the parent cell) known as gametes

Question 9

How does meiosis differ from mitosis?

Answer 9

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 10

What happens during meiosis I?

Answer 10

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

Question 11

What happens during meiosis II?

Answer 11

1. Independent segregation of sister chromatids

2. Each cell divides again, producing 4 haploid cells

Question 12

In which two ways does meiosis produce genetic variation?

Answer 12

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

Results in new combinations of alleles

Question 13

Define population

Answer 13

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

Question 14

What is an allele?

Answer 14

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

Question 15

Define genetic diversity

Answer 15

The total number of different alleles in a population

Question 16

What advantage does a high genetic diversity provide?

Answer 16

The ability to adapt to a change in environment; allows natural selection to occur

Question 17

Explain how natural selection results in development of new characteristics

Answer 17

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 18

What is directional selection?

Answer 18

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

Question 19

Give an example of directional selection

Answer 19

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 20

What is stabilising resistance?

Answer 20

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 21

Give an example of stabilising selection

Answer 21

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

Question 22

Define a niche

Answer 22

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

Question 23

What are three types of adaptation? Give examples of each

Answer 23

Anatomical: changes to the body structure e.g oily fur

Physiological: changes to bodily processes e.g venom production

Behavioural: changes to action e.g hibernation