Meiosis

Question 1

What happens in prophase 1?

Answer 1

• Chromosome condenses and each chromosome supercoils
• Nuclear envelope breaks down, and spindle threads of tubulin protein form from the centriole (animal cells)
• Chromosomes come together in their homolgous pairs
• Crossing over occurs

Question 2

What happens in metaphase 1?

Answer 2

• The pairs of homologous chromosomes, still in their crossed over state, attach along the equator of the spindle
• Each attaches to a spindle thread by its centromere
• Independent assortment occurs
• The way that they line up in metaphase determines how they will segregates indepedently when pulled apart during anaphase

Question 3

What happens in anaphase 1?

Answer 3

• The members of each pair of homologous chromosomes are pulled apart by motor proteins that drag them along the tubulin thread of the spindle
• The centromeres do not divide, each chromosome consists of two chromatids
• The crosed over areas separate from each other

Question 4

What happens in telophase 1?

Answer 4

• The new nuclear envelopes from around each sset of chromosomes (animal cells)
• Each new nucleus contains half the original number of chromosomes but each chromosome consists of two chromatids
• In most plant cells, the cell goes straight from anaphase 1 into prophase 2

Question 5

What happens in prophase 2?

Answer 5

• Nuclear envelope breaks down
• The chromosome coil and condense, each are consisting of two chromatids
• Chromatids of each chromosome are no longer identical, due to crossing over in P1
• Spindles form

Question 6

What occurs in metaphase 2?

Answer 6

• The chromosomes attach, by their centromere, to the equator of the spindle
• Chromatids of each chromosome are randomly arranged

Question 7

What happens in anaphase 2?

Answer 7

• Centromeres divide
• The chromatids of each chromosomme are pulled apart by motor proteins that drag them along the tubulin threads of the spindle, towards opposite poles
• Chromatids therefore randomly segregated

Question 8

What happens in telophase 2?

Answer 8

• Nuclear envelopes form around each of the four haploid nuclei
• Animals - 2 cells now divide to give four haplloid cells
• Plants - A tetrad of four haploid cells is formed