4.3 Genetic diversity can arise as a result of mutation or during meiosis

Question 1

Does meiosis create haploid or diploid cells?

Answer 1

haploid

Question 2

How many divisions occur in meiosis?

Answer 2

2

Question 3

In humans, how many chromosomes do haploid cells have?

Answer 3

23

Question 4

What type of cells does meiosis form?

Answer 4

gametes

Question 5

When does the first division in meiosis occur?

Answer 5

after interphase (after the chromosomes have duplicated in DNA replication)

Question 6

Summarise what happens to chromosomes in meiosis I:

Answer 6

homologous chromosomes are separated from each other

Question 7

Summarise what happens to chromosomes in meiosis II:

Answer 7

the sister chromatids from each chromosome are separated

Question 8

What happens to the chromosomes in prophase I?

Answer 8

they condense, and become visible

Question 9

What happens to the nuclear envelope in prophase I?

Answer 9

breaks down

Question 10

What happens to the spindle fibres in prophase I?

Answer 10

they form from the centrioles

Question 11

What process occurs in prophase I?

Answer 11

crossing over

Question 12

What happens to the chromosomes in metaphase I?

Answer 12

each chromosome lines up to their homologous partner at the equator

Question 13

What happens to the spindle fibres in metaphase I?

Answer 13

they attach to the chromosomes, by attaching to the centromeres

Question 14

What process happens during metaphase I?

Answer 14

independent assortment

Question 15

What happens to the chromosomes during anaphase I?

Answer 15

each chromosome from the homologous pair is pulled apart to opposite ends of the cell

Question 16

Why is anaphase I random?

Answer 16

one out of the pair of homologous chromosome will end up on each side

Question 17

What happens during telophase I?

Answer 17

nuclear envelope reforms around each set of chromosomes and the chromosomes decondense

Question 18

What happens during cytokinesis?

Answer 18

the cytoplasm divides in two

Question 19

Do plant cells undergo cytokinesis in meiosis I?

Answer 19

NO

Question 20

Does interphase occur between meiosis I and meiosis II?

Answer 20

NO

Question 21

What happens to the chromosomes during prophase II?

Answer 21

The DNA condenses and becomes visible

Question 22

What happens to the nuclear envelope during prophase II?

Answer 22

breaks down

Question 23

What happens to the spindle fibre during prophase II?

Answer 23

new spindle fibres form

Question 24

Are the chromatids on each chromosome identical in prophase II? Why/Why not?

Answer 24

NO - due to crossing over in meiosis I

Question 25

What happens to the chromosomes during metaphase II?

Answer 25

they line up at the centre and are randomly assorted to each pole

Question 26

What happens to the spindle fibres during metaphase II?

Answer 26

they attach to the centromere of each chromosome

Question 27

What happens to the spindle fibres during anaphase II?

Answer 27

they contract

Question 28

What happens to the chromatids during anaphase II?

Answer 28

they are pulled to opposite poles (due to the spindle fibres contracting)

Question 29

What happens during telophase II?

Answer 29

the nuclear envelope reforms; the chromosomes de-condense

Question 30

What happens during cytokinesis?

Answer 30

the 2 cells split in two -> making 4 cells

Question 31

Do independent assortment + crossing over happen in meiosis I or meiosis II?

Answer 31

meiosis I

Question 32

What are homologous chromosomes?

Answer 32

chromosomes with the exact set of genes on them, but different alleles

Question 33

What is independent segregation?

Answer 33

The random division of homologous chromosomes into separate daughter cells during meiosis I

Question 34

How does independent segregation increase genetic variation?

Answer 34

there is a large number of possible combinations of chromosomes in the daughter cell produced 2^n (n = number of homologous pairs)

Question 35

What is crossing over?

Answer 35

the exchange of homologous portions of non-sister chromatids

Question 36

How does crossing over increase genetic variation?

Answer 36

new combinations of alleles are formed

Question 37

Does random fertilisation increase genetic variation?

Answer 37

yes - there are 2^n possible chromosome combinations + it is random which egg + sperm will fuse in fertilisation.

Question 38

Define the term mutagenic agent.

Answer 38

A factor that increases the rate of mutations

Question 39

Apart from mutation, explain one other way genetic variation within a species is increased.

Answer 39

- random fertilisation - produces new allele combinations

Question 40

Explain how the chromosome number is halved during meiosis.

Answer 40

- homologous chromosomes - one of each pair goes to each daughter cell

Question 41

Describe the process of crossing over and explain how it increases genetic diversity.

Answer 41

- Homologous pairs of chromosomes form a bivalent - Chiasmata form - lengths of non-sister chromatids / alleles are exchanged - producing new combinations of alleles

Question 42

Name two ways in which meiosis produces genetic variation.

Answer 42

- Independent segregation of homologous chromosomes - crossing over/formation of chiasmata

Question 43

Define 'gene mutation' and explain how a gene mutation can have no effect on an individual.

Answer 43

- Change in the base sequence of DNA - results in the formation of new allele - has no effect because: genetic code is degenerate (so amino acid sequence may not change)

Question 44

Define 'gene mutation' and explain how a gene mutation can have a positive effect on an individual.

Answer 44

- Change in the base sequence of DNA - results in the formation of new allele - + effect = results in change in polypeptide that positively changes the properties of the protein

Question 45

What is the formula for calculating combinations of gametes?

Answer 45

2n (where n is the number of different homologous pairs of chromosomes)

Question 46

What is the formula for calculating combination of offspring?

Answer 46

(2n)2 (where n is the number of different homologous pairs of chromosomes)

Question 47

What is a mutation?

Answer 47

a change in the base sequence of DNA

Question 48

What does a chromosome mutation lead to?

Answer 48

a change in the number of chromosomes present in the zygote after fertilisation has occurred

Question 49

What is non-disjunction?

Answer 49

the bivalent that in anaphase 1 does not separate leading to a gamete with one more than the haploid number (so wrong number of chromosomes in diploid cell after fertilisation)

Question 50

What does a gene mutation lead to?

Answer 50

This is a change in the DNA base sequence forming a new version of a gene or allele and thus a non-functional protein

Question 51

What is a neutral mutation?

Answer 51

a gene mutation that has no effect on survival or reproduction

Question 52

When does gene mutation occur?

Answer 52

during DNA replication

Question 53

What are point mutations?

Answer 53

gene mutations that involve changes in one nucleotide

Question 54

What are the 3 types of point mutation?

Answer 54

- Base deletion - causes from shift to the left - Base substitution - no frame shift - Addition - frame shift to the right

Question 55

How does gene mutation lead to a non-functional mutation?

Answer 55

- DNA triplets are altered - Different mRNA codon - Different amino acid sequence - Non functional protein

Question 56

What are 3 other types of gene mutation?

Answer 56

- Duplication - many bases added so frame shift to the right - Inversion - order of bases in a codon reverses - Translocation - sequence of bases leaves a chromosome and joins another

Question 57

What are mutagenic agents?

Answer 57

Environmental factors that increase the rate of mutation e.g. tobacco smoke, UV rays

Question 58

(i) During which part of the cell cycle are gene mutations most likely to occur? and (ii) Suggest an explanation for your answer ________

Answer 58

Interphase/S/synthesis phase DNA/gene replication/synthesis occurs.

Question 59

(b) Describe how the change in chromosome number in Patau syndrome was produced. (more chromosomes)

Answer 59

b) 1. In meiosis; 2. Homologous chromosomes/sister chromatids do not separate non disjunction

Question 60

(c) Explain why all the cells of the body will have this mutation.

Answer 60

c) 1. Mutation/extra chromosome in gamete/egg/sperm; 2. All cells derived from a single cell/zygote by mitosis.

Question 61

Define the term exon.

Answer 61

Base/nucleotide/triplet sequence coding for polypeptide.

Question 62

(a)  Explain how a single base substitution causes a change in the structure of this polypeptide. Do not include details of transcription and translation in your answer.

Answer 62

a) 1. Change in sequence of amino acids/primary structure; 2. Change in hydrogen/ionic/disulfide bonds; 3. Alters tertiary/3D structure.

Question 63

(b) The faulty allele that causes Ellis-van Creveld syndrome is the result of a mutation of a gene called EVC. This mutation leads to the production of a protein that has one amino acid missing. (i) Suggest how a mutation can lead to the production of a protein that has one amino acid missing.

Answer 63

i) Loss of 3 bases/triplet

Question 64

(ii) Suggest how the production of a protein with one amino acid missing may lead to a genetic disorder such as Ellis-van Creveld syndrome.

Answer 64

1. Change in tertiary structure/active site;** 2. Faulty/non-functional protein/enzyme.