Cell Division

Question 1

What is a sister chromatid

Answer 1

Two identical copies of DNA from when semi-conservative DNA replication occurs joined by centromere

Question 2

How many sister chromatids make up a chromosome

Answer 2

2

Question 3

Prophase I

Answer 3

• 2 uncoiled sets of chromosomes (chromatin) condense to form 4 chromosomes
• Homologous chromosomes pair up (tetrad)
• Crossing over occurs, chromatids from each homologous chromosome exchange equal segments of alleles
• Nuclear membrane dissolves
• Centrioles move to polar ends of cell

Question 4

What is a homologous chromosome

Answer 4

A pair of chromosomes that have the same genes and loci but different alleles (maternal and paternal)

Question 5

What is crossing over

Answer 5

Chromatids from each homologous chromosome exchange equal segments of alleles to increase genetic variability

Question 6

Metaphase I

Answer 6

• Homologous chromosomes line up at equator
• Spindle fibres protrude (from centrioles) attach to centromeres

Question 7

Anaphase I

Answer 7

• Spindle fibres contract and separate homologous chromosomes and pull them to polar opposite sides of cell

Question 8

Telophase I

Answer 8

• Centrioles disappear and nuclear membrane reforms around chromosomes
  (1 chromosome from each homologous pair, x2 2 sister chromatids still, but not identical due to crossing over in P1

Question 9

Prophase II

Answer 9

• No DNA replication (unlike P1)
• Nuclear membrane dissolves
• Spindle fibres align at polar ends of cell

Question 10

Metaphase II

Answer 10

• Chromosomes from each cell line up at equator
• Spindle fibres attach to centromeres

Question 11

Anaphase II

Answer 11

• Sister chromatids separate (spindle fibres contract) and pulled to opposite ends of cell (THEN called chromosomes)T

Question 12

Telophase II

Answer 12

• Spindle fibres disappear and nuclear membrane reforms

Question 13

Cytokinesis I (not separate stage)

Answer 13

• Produces 2 genetically non-identical daughter cells