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

Question 1

Define gene mutations

Answer 1

• Change in the base sequence of DNA of a chromosome

Question 2

What are the 3 types of mutations?

Answer 2

1. Point mutation
2. Frame shift mutation
3. Chromosome mutation

Question 3

Describe point mutations

Answer 3

• Single base substitution - changes the codon so that codon codes for a different amino acid

Question 4

Describe frame shift mutations

Answer 4

• base pair addition or deletion - changes the triplet of bases downstream from the mutation resulting in a frameshift so primary structure of
  polypeptide may be completely different

Question 5

Describe chromosome mutation

Answer 5

• change in chromosome structure and number

Question 6

What does base deletion cause?

Answer 6

• frame shift

Question 7

Which mutation is sickle cell anaemia caused by?

Answer 7

• base substitution in the DNA, resulting in a change of amino acid

Question 8

What is phenylketonuria-PKU?

Answer 8

• disease where the person lacks the enzyme phenylalanine hydroxylase

Question 9

What does lack of enzyme phenylalanine hydroxylase cause?

Answer 9

• build up of phenylalanine

Question 10

What are the symptoms of phenylketonuria-PKU?

Answer 10

1. Paleness, as no melanin is produced
2. Phenylalanine accumulates in blood and tissue fluid – can cause brain damage in children

Question 11

What is a chromosome mutation that causes individuals to have an abnormal number of chromosomes called?

Answer 11

• aneuploidy

Question 12

What do aneuploid cells occur as a result of?

Answer 12

• chromosome breakage or nondisjunction errors that happen during meiosis.

Question 13

What is nondisjunction?

Answer 13

• failure of homologous chromosomes to separate properly during cell division

Question 14

What does nondisjunction cause?

Answer 14

• individuals with either extra or missing chromosomes

Question 15

What can sex chromosome abnormalities that result from nondisjunction lead to?

Answer 15

• conditions such as Klinefelter and Turner syndromes

Question 16

Describe Klinefelter syndrome

Answer 16

• males have one or more extra X sex chromosomes

Question 17

Describe turner syndrome

Answer 17

• In Turner syndrome, females have only one X sex chromosome

Question 18

What is an example of a condition that occurs due to nondisjunction in autosomal (non sex) cells?

Answer 18

• Down syndrome

Question 19

Describe Down syndrome

Answer 19

• have an extra chromosome on autosomal chromosome 21
• translocation of part chromosome 21

Question 20

What are mutagenic agents?

Answer 20

• can increase the rate of mutation

Question 21

What is a diploid?

Answer 21

• containing two complete sets of chromosomes, one from each parent.

Question 22

What is a haploid?

Answer 22

• Containing one complete set of chromosomes

Question 23

What does meiosis produce?

Answer 23

• daughter cells that are genetically different from each other

Question 24

Describe the process of meiosis

Answer 24

1. Prophase 1 - Homologous chromosomes
   pair up, Chromosomes are visible and made of two sister chromatids joined by centromere, Crossing over of, homologous chromosomes
   occur
2. Metaphase 1- Homologous chromosomes
   line up on the equator of the cell
3. Anaphase 1- Homologous chromosomes part
   company and are pulled to opposite poles of the cell

Question 25

Describe the differences between meiosis and mitosis

Answer 25

- meiosis produces four genetically different haploid cells from a diploid cell whereas mitosis produces two genetically identical diploid cells from diploid cell - meiosis undergoes two nuclear divisions whereas mitosis undergoes one division - meiosis undergoes crossing over in prophase 1 results in further genetic variation in daughter cell whereas mitosis does not undergo crossing over

Question 26

What does independent segregation of homologous chromosomes result in?

Answer 26

- genetically different daughter cells

Question 27

What does crossing over between homologous chromosomes result in?

Answer 27

- further genetic variation among daughter cells

Question 28

What is meiosis?

Answer 28

- process of nuclear division in which the chromosome number is halved and variation is introduced into the 4 haploid nuclei produced (gametes)

Question 29

Why is meiosis important?

Answer 29

- ensures that, when the gametes fuse at fertilisation, the normal diploid number of chromosomes is maintained

Question 30

What is the formula used to calculate the possible number of different combinations of chromosomes following meiosis?

Answer 30

- 2^n

Question 31

What does n represent in 2^n?

Answer 31

- haploid number

Question 32

What is the formula used to calculate the possible number of different combinations of chromosomes following random fertilisation?

Answer 32

- (2^n)^2

Question 33

Which two mechanisms in meiosis introduce variation?

Answer 33

1. Independent segregation of homologous chromosomes 2. Crossing over between homologous chromosomes

Question 34

When does independent segregation and crossing over occur?

Answer 34

- in meiosis 1

Question 35

How to identify meiosis in a life cycle?

Answer 35

- find point where diploid (2n) becomes haploid cell (n)

Question 36

What is aneuploidy?

Answer 36

- changes in number of individual chromosomes

Question 37

Which 2 forms can chromosome non disjunction occur in?

Answer 37

1. Polyploidy 2. Aneuploidy

Question 38

What is polyploidy?

Answer 38

- changes in whole sets of chromosomes following random

Question 39

What does polyploidy look like?

Answer 39

- three or more sets of chromosomes rather than usual two

Question 40

Describe how polyploidy occurs in meiosis 1

Answer 40

- 3 homologous chromosomes - each homologous pair is doubled due to DNA replication in interphase - non disjunction in meiosis 1 all chromosomes fail to separate equally - normal division in meiosis 2 chromatids separate equally - 2n gamete (diploid), 2n gamete (diploid) and no chromosomes in gamete - diploid gamete fuses with haploid gamete to form a triploid

Question 41

Describe how polyploidy occurs in meiosis 2

Answer 41

- 3 homologous chromosomes rather than - each homologous pair is doubled due to DNA replication in interphase - normal division in meiosis 1 chromosome separate equally - normal meiosis 2 in one side and non disjunction in meiosis 2 all chromatids fail to separate equally - n gamete (haploid), n gamete (haploid), no chromosomes and 2n gamete (diploid)

Question 42

Describe how aneuploidy occurs in meiosis 1

Answer 42

- 3 homologous chromosomes - each homologous pair is doubled due to DNA replication in interphase - non disjunction in meiosis 1 one chromosome does not separate equally - normal division in meiosis 2 chromatids separate equally - n+1 haploid gamete with one additional chromosome, n+1 haploid gamete with one additional chromosome, n-1 haploid gamete missing one chromosome, n-1 haploid gamete missing one chromosome - n+1 gamete (haploid) fuse with n gamete (haploid) and produce 2n+1 zygote (diploid) - if n-1 gamete (haploid) fuse with n gamete (haploid) produces 2n-1 zygote (diploid)

Question 43

Describe how aneuploidy occurs in meiosis 2

Answer 43

- 3 homologous chromosomes - each homologous pair is doubled due to DNA replication in interphase - normal division in meiosis 1 - non disjunction in meiosis 2 one chromatid fails to separate equally - n-1 haploid gamete missing one chromosome, n+1 haploid gamete with one additional chromosome, n haploid gamete and n haploid gamete