Meiosis

Question 1

What is meiosis?

Answer 1

A reduction division of the nucleus to form haploid gametes

Question 2

What are daughter cells?

Answer 2

• Cells formed from cell division

- Meiosis generates 4 haploid daughter cells. Each has a unique mix of half the genetic information of the parent cell

Question 3

What happens during meiosis?

Answer 3

• Chromosome number is halved during gamete production
• Diploid parent cell produces 4 haploid daughter cells
• Takes place in reproductive organs
• Parent cell must divide twice; meiosis I and meiosis II

Question 4

Outline interphase

Answer 4

• Chromosomes replicate
• Occurs during synthesis (S) phase through DNA replication
• Each chromosome becomes a pair of sister chromatids, physically joined at the equator

Question 5

Outline prophase I

Answer 5

• Homologus chromosomes associate with each other
• Crossing over between non-sister chromatids can take place between homologus chromosomes
• Nuclear membrane breaks down and centrioles migrate to the poles
• Results in recombination of alleles, a source of genetic variation

Question 6

What is crossing over?

Answer 6

• Unique to meiosis
• Genetic material is exchanged between non-sister chromatids
• 2 homologus chromatids break at the same point, twist around each other and connect to the other’s initial position
• Allows DNA from maternal chromosome to mix with DNA from paternal chromosome

Question 7

Outline metaphase I

Answer 7

• Homologus pairs (bivalents) line up at the equator

- Random orientation of homologus pairs leads to genetic variation in gametes

Question 8

Outline anaphase I

Answer 8

• Spindle fibres contract
• Homologus pairs are seperated and pulled to opposing poles (reduction division)
• Non-disjunction will affect the chromosome number of all 4 gametes

Question 9

Outline telophase I

Answer 9

• New nuclei forma and cytoplasm begins to divide by cytokinesis
• Nuclei are no longer diploid
• Each contain one pair of sister chromatids for each of the species’ chromosomes
• If crossing over and recombination has occurred, then sister chromatids will not be exact copies

Question 10

What is cytokinesis?

Answer 10

• Occurs at the end of meiosis I
• Cell splits into 2 seperate cells
• Cells are haploid
• Meiosis II follows

Question 11

Outline prophase II

Answer 11

• Nuclei breaks down
• No crossing over occurs
• Chromosomes condense and become visible

Question 12

Outline metaphase II

Answer 12

• Pair of sister chromatids align at the equator, spindle fibres form and attach at the centromeres

Question 13

Outline anaphase II

Answer 13

• Spindle fibres contract and centromeres are broken
• The pairs of sister chromatids are pulled to opposing poles
• Non-disjunction wil lead to two gametes containing the wrong chromosome number

Question 14

Outline telophase II

Answer 14

• New haploid nuclei are formed
• Cytokinesis begins, splitting the cells
• The end result of meiosis is 4 haploid gamete cells
• Fertilisation of these haploid gametes will produce a diploid zygote