Diversity, Classification and Variation- Meiosis and Genetic Variation

Question 1

What are gametes?

Answer 1

The sperm cells in males and egg cells in females

Question 2

When do the sperm and egg cells join together?

Answer 2

Fertilisation

Question 3

What is formed at fertilisation?

Answer 3

A zygote which divides and develops into a new organism

Question 4

How many chromosomes do normal body cells have?

Answer 4

The diploid number (2n)- each cell contains 2 of each chromosome, one from the mum, one from the dad

Question 5

How many chromosomes do gametes have?

Answer 5

A haploid number (n)- only one copy of each chromosome

Question 6

What happens at fertilisation?

Answer 6

A haploid sperm fuses with a haploid egg to make a cell with the normal diploid number of chromosomes- half of chromosomes are from the father and half are from the mother

Question 7

What does random fertilisation produce?

Answer 7

Zygotes with different combinations of chromosomes to both parents

Question 8

What is the advantage of random fertilisation?

Answer 8

Mixing of genetic material increases genetic diversity within a species

Question 9

What is meiosis?

Answer 9

A type of cell division

Question 10

Where does meiosis take place?

Answer 10

In the reproductive organs

Question 11

What kind of cells are the cells that divide by meiosis?

Answer 11

Diploid

Question 12

What kind of cells are the cells that are formed from meiosis?

Answer 12

Haploid

Question 13

What would happen without meiosis?

Answer 13

You’d get double the number of chromosomes when the gametes fused

Question 14

What happens before meiosis starts?

Answer 14

DNA unravels and replicates so that there are two copies of each chromosomes called chromatids

Question 15

What happens after chromatids are formed?

Answer 15

DNA condenses to form double-armed chromosomes that are each made from two sister chromatids

Question 16

What are the sister chromatids joined by?

Answer 16

A centromere

Question 17

What happens in meiosis I?

Answer 17

The chromosomes arrange themselves into homologous pairs which are then separated, halving the chromosome number

Question 18

What happens in meiosis II?

Answer 18

The pairs of sister chromatids that make up each chromosome are separated

Question 19

What is produced in meiosis?

Answer 19

Four haploid cells that are genetically different from each other

Question 20

What does the chromatids crossing over in meiosis I mean?

Answer 20

Chromatids still contain same genes but now have a different combination of alleles

Question 21

How does crossing over of chromatids lead to genetic variation?

Answer 21

Means that each of the four daughter cells formed contains chromatids with different alleles

Question 22

How does independent segregation of chromosomes lead to genetic variation?

Answer 22

1. Each homologous pair of chromosomes is made up of one maternal chromosome and one paternal chromosome
2. When homologous pairs are separated, it’s completely random which chromosome from each pair ends up in which daughter cell
3. So four daughter cells produced have different combinations of maternal and paternal chromosomes
4. Called independent segregation of chromosomes
5. Shuffling of chromosomes leads to genetic variation in potential offspring

Question 23

How is mitosis different from meiosis?

Answer 23

Mitosis- produces cells with same number of chromosomes as parent cell, daughter cells are genetically identical to each other and parent cell, two daughter cells produced
Meiosis- produces cells with half the number of chromosomes as parent cell, daughter cells are genetically different from one another and parent cell, four daughter cells produced

Question 24

What happens if meiosis goes wrong?

Answer 24

Cells produced contain variations in the numbers of whole chromosomes or parts of chromosomes- chromosome mutation

Question 25

What can chromosome mutations lead to?

Answer 25

Inherited conditions because error is in the gametes