Module 2 : Section 6 - Sexual Reproduction and Meiosis

Question 1

What does meiosis produce

Answer 1

Gametes for sexual reproduction

Question 2

What happens in sexual reproduction

Answer 2

In sexual reproduction two gametes join together at fertilisation to form a zygote. The zygote then divides and develops into a new organism

Question 3

What is meiosis

Answer 3

• A type of cell division that happens in the reproductive organs to produce gametes
• Meiosis involves a reduction division
• cells that have the full number of chromosomes to start to with, but the cells that formed from meiosis have half the number

Question 4

What are haploid cells

Answer 4

Cells with half the normal number of chromosomes

Question 5

Cells formed by meiosis are….

Answer 5

Genetically different because each new cell ends up with a different combination of chromosomes

Question 6

Meiosis involves…

Answer 6

Two divisions:
- Meiosis I
- Meiosis II

Question 7

Which meiosis division is the reduction division

Answer 7

Meiosis I is the reduction division (halves the chromosomes number)

Question 8

What stages are meiosis I and meiosis II broken up into

Answer 8

Like mitosis:
- Prophase
- Metaphase
- Anaphase
- Telophase

Question 9

When does the whole of meiosis begin

Answer 9

With interphase. During interphase, the DNA unravels and replicates to produce double-armed chromosomes called sister chromatids

Question 10

What happens in prophase I in meiosis I

Answer 10

• Chromosomes condense, getting shorter and fatter
• Chromosomes then arrange themselves into homologous and crossing over occurs
• centrioles start moving opposite ends of the cells forming spindle fibres
• nuclear envelope breaks down

Question 11

What happens in metaphase I in meiosis I

Answer 11

• homologous pairs line up across the centre of the cell and attach to the spindle fibres by the centromere

Question 12

What happens in anaphase I in meiosis I

Answer 12

• spindles contract separating the homologous pairs - one chromosomes goes to each end of the cell

Question 13

What happens in telophase I in meiosis I

Answer 13

• A nuclear envelope forms around each group of chromosomes

Question 14

What happens in cytokinesis in meiosis I

Answer 14

• Cytokinesis (division of the cytoplasm) occurs and two haploid daughter cells are produced

Question 15

What happens in meiosis II (second division)

Answer 15

• The two daughter cells undergo prophase II, metaphase II, anaphase II, telophase II, which are a lot like the stages in mitosis

Question 16

What happens in anaphase II in meiosis II

Answer 16

• the pairs of sister chromatids are separated
• each new daughter cell inherits one chromatid from each chromosome
• four genetically different haploid cells are produced
• these are gametes

Question 17

What happens in prophase I to the chromatids

Answer 17

• During prophase I of meiosis I, homologous pairs of chromosomes come together and pair up
• the chromatids twist around each other and bits of chromatids swap over
• the chromatids still contain the same genes but now have a different combination of alleles

Question 18

What two main events that happen during meiosis lead to genetic variation

Answer 18

• Crossing over of chromatids
• independent assortment of chromosomes

Question 19

What does the crossing of chromatids refer to

Answer 19

The crossing over of chromatids in meiosis I means that each of the four daughter cells formed from meiosis contains chromatids with different alleles

Question 20

What does independent assortment of chromosomes refer to

Answer 20

• each homologous pair of chromosomes in your cells is made up of one chromosome from your mum and one chromosome from your dad
• when the homologous pairs line up in metaphase I and are separated in anaphase I, it’s completely random which chromosome from each pair ends up in which daughter cell
• so the four daughter cells produced by meiosis have completely different combinations of those maternal and paternal chromosomes
• this is called independent assortment of the chromosomes
• this ‘shuffling’ of chromosomes leads to genetic variation in any potential offspring