3.3.4 - Meiosis: Source Of Genetic Variation

Question 1

What Meiosis?
(3 Points)

Answer 1

~ Gives rise to cells that are genetically different from each other.

~ Happens in the reproductive organs to produce gametes.

~ The nucleus of the original parent cell undergoes two rounds of division.

Question 2

What Are The 2 Rounds Of Meiosis?

Answer 2

~ Meiosis one.

~ Meiosis two.

Question 3

Describe Meiosis One
(4 Points)

Answer 3

~ DNA replicates, so there are two identical copies each chromosome, called chromatids.

~ DNA condenses to form double-armed chromosomes, made from two sister chromatids.

~ Chromosomes then arrange themselves into homologous pairs.

~ The homologous pairs are separated, halving the number of chromosomes (From 2n -> n).

Question 4

Describe Meiosis Two
(3 Points)

Answer 4

~ The pairs of sister chromatids are separated.

~ Four daughter cells that are genetically different from each other a produced.

~ Known as gametes.

Question 5

What Are The Mechanisms That Meiosis Has That Increase The Genetic Diversity Of The Gametes Produced?
(2 Points)

Answer 5

~ Crossing over of chromatids.

~ Independent assortment of chromosomes.

Question 6

Describe ‘Crossing Over Of Chromatids’ During Meiosis
(6 Points)

Answer 6

~ Before meiosis one, homologous pairs of chromosomes come together and pair up very close to each other.

~ Two of the chromatids in each homologous pair cross over and can become entangled. These crossing points are known as the chiasmata.

~ This entanglement places stress on the DNA molecules.

~ As a result the crossed over parts break off their original chromatid and rejoin onto the other chromatid, recombining their genetic material.

~ The chromatids still contain the same genes but they now have a different combination of alleles.

~ Meaning that each of the four new cells formed from meiosis contains chromatids with different alleles.

Question 7

Describe ‘Independent Assortment Of Chromosomes’ During Meiosis
(4 Points)

Answer 7

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

~ The different combinations of chromosomes in daughter cells increases the genetic variation between gametes.

~ The homologous chromosomes are then separated and pulled apart to different poles.

~ The combination of alleles that end up in each daughter cell depends on how the pairs of homologous chromosomes were lined up.

Question 8

How Can You Work Out The Number Of Different Possible Chromosome Combinations?
(3 Points)

Answer 8

~ Using -> 2n.

~ N = Number of chromosomes in a haploid cell.

~ E.g. 2n(23) = 8,324,608 different combinations.