Meiosis

Question 1

Homologous Chromosomes

Answer 1

Chromosomes that code for the same information

Pair of chromosomes carrying different alleles of the same gene (e.g. eye colour)

Question 2

Describe the difference between mitosis and meiosis

Answer 2

Mitosis: involves cell division that ensures both daughter cells receive a full set of identical chromosomes (diploid cells)

Meiosis
Division process that prevents “doubling” of genetic material from occurring
Creates gametes with half the number of chromosomes (haploid cells)

Question 3

Stages of meiosis

Answer 3

Prior to the start of meiosis, cell undergoes S Phase (chromosome replication)
Meiosis has two rounds of cell division:
Meiosis I
Meiosis II
Each round is divided into 4 sub phases:
Prophase, Metaphase, Anaphase, Telophase

Question 4

Purpose of Meiosis 1

Answer 4

number of chromosomes reduced from diploid 2n to haploid n)

Question 5

Prophase I (early- diploid)

Answer 5

• Chromosomes condense & shorten, visible
• Spindle fibres form
• Centrioles move toward poles

Homologous chromosomes pairs form a tetrad made of 4 sister chromatids

Question 6

Prophase I (late-diploid)

Answer 6

• In the tetrad, chromatids often break at the end and swap places with the sister chromatid (recombination/crossing over)
• allows for genetic variation
• location of recombination is called the chiasma

Question 7

Metaphase I (diploid)

Answer 7

• Tetrads line up along equator randomly

- Spindle fibres attach to each pair of sister chromatids

Question 8

Anaphase I (diploid)

Answer 8

• The sister chromatids do NOT separate here (different than mitosis)
• Instead, the pairs of chromosomes move apart to opposite poles

Question 9

Telophase I (haploid)

Answer 9

• Chromosomes condense slightly, nuclear membrane may form
• Cytokinesis occurs forming two genetically different daughter cells
• Each daughter cell has haploid chromosome number (n=2) with each chromosome consisting of a pair of sister chromatids

Question 10

Meiosis ll

Answer 10

-Cells are haploid, no duplication of chromosomes during a very short interphase (no G1 or S phase)
Each chromosome (made of two "mixed" chromatids) lines up at equator, centromeres split, and each chromosome is pulled to opposite poles
End result – 4 haploid cells

Question 11

Prophase II (haploid)

Answer 11

• Nuclear envelope begins to break down
• Spindle fibres begin to form
• Centrioles begin to move to poles

Question 12

Metaphase II (haploid)

Answer 12

• Chromosomes align along equator of cell

- Spindle fibres attach to centromeres of sister chromatids

Question 13

Anaphase II (haploid)

Answer 13

Spindle fibres contract and pull sister chromatids apart

Question 14

Telophase II (haploid)

Answer 14

• Nuclear envelope assembles
• Chromosomes decondense
• Spindle disappears
• Cytokinesis divides each cell into two

Question 15

Results of meiosis

Answer 15

4 haploid gamete cells (n=2)
1 copy of each chromosome
1 allele of each gene
Different combinations of alleles for different genes along the chromosome