2.1.6 - Cell division (set B - Meiosis)

Question 1

Define the term diploid cells?

Answer 1

Diploid is a term that refers to the presence of two complete sets of chromosomes in an organism’s cells, with each parent contributing a chromosome to each pair

Question 2

Define the term haploid cells?

Answer 2

Haploid describes a cell that contains a single set of chromosomes - gametes are haploid cells that contain 23 chromosomes

Question 3

What is meiosis?

Answer 3

Cell division known as reducing division, the nucleus divides twice to produce four haploid daughter cells

Question 4

What are alleles, what do they do?

Answer 4

Different versions of the same gene and contribute to the organisms phenotype

Question 5

What are the two divisions of meiosis?

Answer 5

• meiosis 1 - reduction division when the pairs of homologous chromosomes are separated into two haploid cells
• meiosis 2 - second division, pairs of chromatids present in each daughter cell are separated - forming two more haploid cells

Question 6

Explain what happens during prophase 1?

Answer 6

Chromatin condense into chromosomes, the nuclear envelope disintegrates and the nucleolus disappears

• chromosomes pair up forming bivalents - movement of chromosomes through liquid cytoplasm result in ‘crossing over’

Question 7

Explain what happens during metaphase 1?

Answer 7

Homologous pairs of chromosomes assemble randomly and independently along metaphase plate - process called independent assortment

• independent assortment of chromosomes results in genetic variation

Question 8

What is independent assortment?

Answer 8

Takes place in metaphase 1 and is when homologous chromosomes line up at the equator as bivalents in one of two arrangements - due to spindle fibres connecting at centromeres and aligning them

Question 9

Explain what happens during anaphase 1?

Answer 9

Spindle fibres contract and split the bivalent, homologous chromosomes separate - each homologous chromosomes move to opposite sides of the cell

Question 10

Explain in depth the ‘crossing over’ during prophase 1?

Answer 10

Homologous chromosomes undergo synapsis whereby they pair up to form a bivalent - the chromosomes are held together at points called chiasmata

• crossing over of genetic material occurs at the chiasmata

Question 11

Explain what happens during telophase 1?

Answer 11

chromosomes assemble at each pole and decondense, nuclear envelope may reform

• cell undergoes cytokinesis to form two haploid cells

Question 12

Explain what happens during prophase 2?

Answer 12

Beginning of second division, chromomes pair up and re-condense, spindle fibres reform and centrioles move to opposite poles of the cell

• nuclear envelope breaks down

Question 13

Explain what happens during metaphase 2?

Answer 13

Chromosomes (sister chromatids) assemble on the metaphase plate moved by spindle fibres

• more independent assortment - so more genetic variation

Question 14

Explain what happens during anaphase 2?

Answer 14

Chromatids of individual chromosomes are pulled to opposite poles after division of the centromeres by contracting spindle fibres

Question 15

Explain what happens during telophase 2?

Answer 15

Chromatids assemble at the poles, the chromosomes uncoil and form chromatin again , spindle fibres break down - cell undergoes cytokinesis

• nuclear envelope reforms and nucleolus is visible

4 haploid daughter cells produced

Question 16

Product at meosis 2?

Answer 16

4 haploid daughter cells are produced

Question 17

Explain what happens during cytokinesis?

Answer 17

Cytoplasms and surface membrane divide - creating four independent haploid daughter cells