Meiosis (f,g)

Question 1

What is meiosis?

Answer 1

The production of gametes - a reduction division producing haploid cells

Question 2

Why is meiosis important?

Answer 2

Because it produces genetically different gametes which will then fuse to form a zygote - diploid - to grow into an individual with variation

Question 3

What are homologous chromosomes?

Answer 3

Matching pairs of chromosomes, one inherited from each parent. Each chromosome in a homologous pair has the same genes at the same loci.

Question 4

What are alleles?

Answer 4

Different versions of the same genes, gene variants. Different alleles of a gene will have the same locus.

Question 5

Describe prophase 1

Answer 5

• chromosomes condense getting shorter + fatter
• nuclear envelope disintegrates
• centrioles move to form spindle fibres
• homologous chromosomes pair up + crossing over occurs

Question 6

Describe metaphase 1

Answer 6

• homologous pairs line up along the metaphase plate and attach spindle fibres by their chromosomes
• independent assortment occurs

Question 7

Describe anaphase 1

Answer 7

• homologous chromosomes are pulled to the opposite poles and the chromatids stay joined to each other

Question 8

Describe telophase 1

Answer 8

• chromosomes assemble at each pole and uncoil
• nuclear envelope reforms
• cytokinesis occurs + divides into 2 cells. Haploid, so is a reduction division

Question 9

Describe prophase 2

Answer 9

• chromosomes (still consist of 2 chromatids), condense + become visible again
• nuclear envelope disintegrates + spindle formation begins

Question 10

Describe metaphase 2

Answer 10

• individual chromosomes assemble on the metaphase plate

Question 11

Describe anaphase 2

Answer 11

• chromatids of the individual chromosomes are pulled to opposite ends after division of the centromeres

Question 12

Describe telophase 2

Answer 12

• chromatids assemble at the poles
• chromosomes uncoil + form chromatin again
• nuclear envelope reforms

Question 13

Describe cytokinesis

Answer 13

2 cells divide to form 4 genetically different cells in total

Question 14

How does crossing over create variation?

Answer 14

• As the chromosomes move through the liquid cytoplasm, the chromatids twist around each other + bit swap over. They still contain the same genes but now have a different combination of alleles.
• point of breakage = chiasmata

Question 15

How does independent assortment cause genetic variation?

Answer 15

• The orientation of each homologous pair - in metaphase 1 - on the metaphase plate is random and independent of any other homologous pair
• maternal or paternal chromosomes can end of racing either pole
• can result in many different combinations of alleles facing the poles