genetic diversity can arise as a result of mutation/meiosis

Question 1

Define a mutation

Answer 1

Change to the base sequence of DNA caused by errors during DNA replication

Question 2

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

Answer 2

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

Question 3

Describe what a substitution mutation is

Answer 3

When a nucleotide in the DNA sequence is replaced by another

Question 4

Describe what a deletion mutation is

Answer 4

When a nucleotide in the DNA sequence is lost, leads to a frameshift which means the entire amino acid sequence is different

Question 5

What is a mutagenic agent?

Answer 5

They are things/factors that can cause an increase in the rate of gene mutations

Question 6

Give examples of mutagenic agents

Answer 6

1. X-rays
2. UV light
3. Chemicals in alcohol/tobacco

Question 7

What is a chromosome non-disjunction

Answer 7

When chromosomes fail to separate correctly in meiosis, resulting in gametes with 1 more or fewer chromosomes than normal

Question 8

Define meiosis

Answer 8

A form of cell division that produces 4 genetically different haploid cells known as gametes

Question 9

What is a duplication mutation?

Answer 9

One or more bases are repeated

Question 10

What is an insertion mutation?

Answer 10

One extra base is added

Question 11

What is an inversion mutation?

Answer 11

A sequence of bases is reversed

Question 12

What is a point mutation?

Answer 12

A change in a single nucleotide

Question 13

When are mutations likely to occur?

Answer 13

DNA replication

Question 14

Describe the differences between mitosis and meiosis

Answer 14

1. Mitosis produces cells with the same number of chromosomes as the parent cell, meiosis produces cells with half the number of chromosomes as the parent cell
2. In mitosis the daughter cells are genetically identical to the parent cell and to each other, in meiosis, the daughter cells are genetically different from one another and the parent cell
3. Mitosis produces 2 daughter cells, meiosis produces 4 daughter cells

Question 15

Define gametes

Answer 15

Gametes are sex cells

Question 16

What is a zygotes

Answer 16

When a sperm cell and an egg cell fuse together in fertilisation

Question 17

Define diploid

Answer 17

Each cell contains two of each chromosome from both parents (46 chromosomes)

Question 18

Define haploid

Answer 18

Each cell contain one copy of each chromosome (23 chromosomes)

Question 19

Describe what happens at fertilization

Answer 19

• Haploid sperm fuses with a haploid egg
• Making a cell with a diploid number of chromosome
• Half of the chromosomes are from the mum and dad

Question 20

Describe random fertilization

Answer 20

Produces zygotes with different combinations of chromosomes to both parents

Question 21

How is the mixing of genetic material advantageous to a species?

Answer 21

The mixing of genetic material in sexual reproduction increases genetic diversity within a species

Question 22

Describe the cells before meiosis takes place

Answer 22

They are diploid cells (46 chromosomes)

Question 23

Describe the cells after meiosis takes place

Answer 23

They are haploid cells (1/2 number of chromosomes)

Question 24

Describe the steps of meiosis

Answer 24

1. DNA unravels and replicates so there are 2 copies of each chromosome (chromatids)
2. DNA condenses to form two sister chromatids joined together by a centromere
3. Meiosis I - the chromosomes arrange themselves into homologous pairs
4. Homologous pairs are separated, halving the chromosome number
5. Meiosis II - the centromere of each sister chromatid is divided
6. 4 haploid cells (gametes) that are genetically different from each other are produced

Question 25

In which ways does meiosis produce genetic variation?

Answer 25

1. Crossing over of chromatids during meiosis I
2. Independent segregation of chromosomes

Question 26

Explain how the independent segregation of chromosomes leads to genetic variation

Answer 26

• Homologous pairs of chromosomes are made up of 1 chromosome from each parent
• When they are separated in meiosis I, it is completely random which chromosome from each pair ends up in which daughter cell
• So the 4 daughter cells produced by meiosis have different combinations of maternal and paternal chromosomes