9.4 - Meiosis in plants and animal cells

Question 1

What is meiosis? what does it produce and used for? how many divisions does it have?

Answer 1

• a form of nuclear division that results in the production of haploid cells from diploid cells
• produces gametes in plants & animals which is used for sexual reproduction
• has 2 divisions

Question 2

What occurs in Prophase I of meiosis?

Answer 2

• DNA condenses and becomes visible as chromosomes
• DNA replication already occurs in S1 stage of the cell cycle

2 sister chromatids are joined by a centromere

• chromosomes are arranged side by side in homologous pairs
• due to them being close together, crossing over of non-sister chromatids and chiasma/chiasmata (point of crossing over occurs)
• the centrioles migrate to the opposite poles and the spindle is formed
• nuclear envelope breaks down and the nucleolus disintegrates

Question 3

What is a pair of homologous chromosomes known as?

Answer 3

a bivalent

Question 4

What occurs in Metaphase I?

Answer 4

the bivalents line up along the equator of the spindle
* the spindle fibres are attached to the centromeres

Question 5

What occurs in Anaphase I?

Answer 5

the homologous paris of chromosomes are separated as the microtubules pull whole chromosomes to opposite ends of the spindle
* centromeres don’t divide

Question 6

What occurs in Telophase I?

Answer 6

• the chromosomes arrive at opposite poles
• spindle fibres start to break down
• nuclear envelopes form around the two groups of chromosomes and the nucleoli reform
• some plant cells go straight into meiosis II without the reformation of the nucleus

Question 7

What happens in cytokinesis?

Answer 7

• when the division of the cytoplasm occurs
• organelles get distributed between the two developing cells
• end product of cytokinesis in meiosis I is 2 haploid cells - contain half the number of centromeres

Question 8

What happens in cytokinesis for animal cells?

Answer 8

in animal cells the cell surface membrane pinches inwards forming a cleavage furrow in the middle of the cell which contracts - divides the cytoplasm in half

Question 9

What happens in cytokinesis for plant cells?

Answer 9

in plant cells, vesicles from the Golgi apparatus gather along the equator of the spindle and the vesicles merge together to form the new cell surface membrane and also secrete calcium pectate which becomes the middle lamella
* layers of cellulose lay upon the middle lamella to form the primary and secondary walls of the cell

Question 10

What occurs in meiosis II, compare it with meiosis I:

Answer 10

no interphase
* DNA isn’t replicated

second division is almost identical to the first

Question 11

What happens in prophase II?

Answer 11

• the nuclear envelope breaks done and the chromosomes condense
• spindle forms at a right angle to the old one

Question 12

What happens in metaphase II?

Answer 12

chromosomes line up in a single file along the equator of the spindle

Question 13

What occurs in Anaphase II?

Answer 13

• centromeres divide and individual chromatids are pulled to opposite poles
• creates 4 groups of chromosomes that have half the no. of chromosomes that have half the no. of chromosomes compared to the original parent cell

Question 14

What occurs in Telophase II?

Answer 14

nuclear membranes form around each group of chromosomes

Question 15

What occurs in cytokinesis II?

Answer 15

cytoplasm divides as new cell surface membranes are formed creating 4 haploid cells
* cells still contain the same number of centromeres as they did at the start of meiosis I - they only have half the no. of chromosomes