MEIOSIS

Question 1

what is the process of crossing over? (3)

Answer 1

• homologous chromosomes pair up in very close proximity to each other (called bivalents).
  -the non sister chromatid can cross over and get entangled, these crossing points are called chiasmata.
  -these entanglement place stress on the DNA molecules as a result a section of chromatid from one chromosome may break and re join with the chromatid from the other chromosome.

Question 2

what is meant by crossing over? (1)

Answer 2

the process by which non-sister chromatids exchange alleles.

Question 3

why is crossing over significant? (1)

Answer 3

it can result in a new combination of alleles on the two chromosomes.

Question 4

what is the process of independent assortment? (3)

Answer 4

-homologous chromosomes pair up and are pulled towards the equator of the spindle.
-each pair can be arranged with either chromosome on top, the orientation of the homologous pair is independent/unaffected by the orientation of any other pair, they are then separated.

Question 5

what is meant by independent assortment? (1)

Answer 5

the production of different combinations of alleles in daughter cells due to the random alignment of homologous chromosome pairs along the equator of the spindle during meiosis 1.

Question 6

what occurs in meiosis 1? (1)

Answer 6

the homologous pairs of chromosomes are split up to produce two haploid nuclei (each chromosome still consists of 2 chromatids)

Question 7

what occurs in meiosis 2? (1)

Answer 7

the chromatids that make up each chromosome separate to produce 4 haploid nuclei (each consist of a single chromatid)

Question 8

how is mitotic index calculated? (1)

Answer 8

mitotic index = number of cells with visible chromosomes / total number of cells

Question 9

what are the two rounds of division in meiosis? (2)

Answer 9

meiosis 1
meiosis 2