GVR: Genetic variation from mutation or meiosis

Question 1

What is a zygote?

Answer 1

The diploid cell formed when two gametes fuse during fertilisation.

Question 2

What is a diploid cell?

Answer 2

A cell that contains two copies of each chromosome.

Question 3

What is a haploid cell?

Answer 3

A cell that contains one copy of each chromosome.

Question 4

Explain crossing over:

Answer 4

1) During meiosis I homologous chromosomes come together and form a bivalent.
2) They overlap at their chiasmata.
3) Allele exchange occurs.

Question 5

What are nondisjunction events?

Answer 5

Failure of homologous pairs/sister chromatids to separate in anaphase I or II.

Question 6

Explain nondisjunction of homologous chromosomes in meiosis I:

Answer 6

• Homologous chromosomes fail to separate in meiosis I (nondisjunction).
• One gamete has 3 sets of chromosomes, the other gamete has 1 set.
• Gametes divide so 2 gametes have an extra chromosome, and 2 gametes are missing a chromosome.

Question 7

Explain nondisjunction of sister chromatids in meiosis II:

Answer 7

• Meiosis I occurs normally.
• Sister chromatids fail to separate in one gamete during meiosis II.
• Abnormal gamete divides so one gamete has an extra chromosome and the other gamete is missing a chromosome.
• Other healthy gamete divides to produce 2 normal haploid gametes.

Question 8

What is a trisomy disorder?

Answer 8

When a gamete has 3 sets of chromosomes instead of 2.

Question 9

Give an example of a trisomy disorder:

Answer 9

Down syndrome

Question 10

How many homologous pairs does a human have?

Answer 10

23

Question 11

What is the diploid number for humans?

Answer 11

46

Question 12

Gametes have a ______ number of chromosomes.

Answer 12

Haploid.

Question 13

What is the haploid number for humans?

Answer 13

23

Question 14

Cells that divide by meiosis are ______, and the cells that are formed by meiosis are _______.

Answer 14

Diploid
Haploid

Question 15

Explain the 6 step process of meiosis:

Answer 15

1) Before meiosis starts, DNA unravels and replicate so there are to copies of each chromosome (chromatids).
2) DNA condenses to form double-armed chromosomes, each made from two sister chromatids joined by their centromere.
3) Meiosis I - the chromosomes arrange themselves into homologous pairs.
4) Homologous pairs are separated- halving the chromosome number.
5) Meiosis II - The pairs of sister chromatids that make up each chromosome are separated.
6) Four haploid cells that are genetically different from each other are produced.

Question 16

Why is crossing over advantageous for meiosis II?

Answer 16

Means that each of the 4 daughter cells contain chromatids with different alleles.

Question 17

What are the two ways normal genetic variation occurs in meiosis?

Answer 17

• Crossing over
• Independent segregation

Question 18

What happens in independent segregation?

Answer 18

Homologous chromosomes are randomly distributed to daughter cells

Question 19

Define independent segregation:

Answer 19

The random separation of homologous chromosomes in meiosis I that produces genetic variation.

Question 20

What is a substitution mutation?

Answer 20

One base is substituted with another.

Question 21

What is a deletion mutation?

Answer 21

One base is deleted.

Question 22

What are mutagenic agents?

Answer 22

Factors that can cause an increase in the rate of mutations.

Question 23

Give 3 examples of mutagenic agents:

Answer 23

• Ultraviolet rays
• Ionising radiation
• Tobacco