Meiosis

Question 1

Prophase 1

Answer 1

• chromatin condenses
• each chromosome supercoils
• nuclear envelope breaks down and spindle threads of tubulin from form from the centrioles
• the chromosomes come together in homologous pairs
• each member consist of two sister chromatids
• crossing over occurs where non sister chromatids wrap around each other and swap sections so that alleles are shuffled

Question 2

Metaphase 1

Answer 2

• pairs of homologous chromosomes I there crossed over state attach along the equator of the spindle
• they attach to the spindle thread by its centromere
• the homologous pairs are arranged randomly wit members of each pair facing opposite poles of the cell this is independent assortment
• the way they line up here determines how they will segregate independently when pulled apart during anaphase

Question 3

anaphase 1

Answer 3

• the members of each pair of homologous chromosomes are pulled apart by motor proteins these drag them along the tubulin threads of the spindle
• centromeres do not divide and each chromosomes consists of two chromatids
• the crossed over areas separate from each other, this results in the swapped areas of chromosome and allele shuffling

Question 4

telophase 1

Answer 4

• in most animal cells two new nuclear envelopes form around each set of chromosomes, cell divides by cytokinesis, there is then a short interphase when the chromosomes uncoil
• each new nucleus contains half the original number of chromosomes but each chromosome consist of two chromatids
• in plant cells the cell goes straight from anaphase 1 into prophase 2

Question 5

Prophase 2

Answer 5

• if the nuclear envelope has reformed then they now break down
• the chromosomes coil and condense each one consisting of two chromatids
• the chromatids of each chromosome are no longer identical due to crossing over in prophase 1
• spindles form

Question 6

metaphase 2

Answer 6

• the chromosomes attach by their centromere to the equator of the spindle
• the chromatids of each chromosome are randomly arranged
• the way they arrange will determine how the chromatid separate during anaphase

Question 7

anaphase 2

Answer 7

• centromeres divide
• the chromatids of each chromosome are pulled apart by motor proteins that drag them along the tubulin threads of the spindle towards the opposite poles
• the chromatids are therefore randomly segregated

Question 8

telophase 2

Answer 8

• nuclear envelopes for around each of the four haploid nuclei
• in animals the two cells now divide to giver four haploid cells
  in plants a tetrad of four haploid cells is formed