Topic 3.3: Meiosis

Question 1

Define meiosis

Answer 1

Meiosis is the process by which sex cells (gametes) are made in the reproductive organs

It involves the reduction division of a diploid germline cell into four genetically distinct haploid nuclei

Question 2

Define sister chromatids

Answer 2

The two identical DNA molecules are identified as sister chromatids, and are held together by a single centromere

Question 3

What happens during prophase I of meiosis I?

Answer 3

Chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs

Question 4

What happens during metaphase I of meiosis I?

Answer 4

Spindle fibres from opposing centrosomes connect to bivalents (at centromeres) and align them along the middle of the cell

Question 5

What happens during anaphase I of meiosis I?

Answer 5

Spindle fibres contract and split the bivalent, homologous chromosomes move to opposite poles of the cell

Question 6

What happens during telophase I of meiosis I?

Answer 6

Chromosomes decondense, nuclear membrane may reform, cell divides (cytokinesis) to form two haploid daughter cells

Question 7

What happens during prophase II of meiosis II?

Answer 7

Chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before)

Question 8

What happens during metaphase II of meiosis II?

Answer 8

Spindle fibres from opposing centrosomes attach to chromosomes (at centromere) and align them along the cell equator

Question 9

What happens during anaphase II of meiosis II?

Answer 9

Spindle fibres contract and separate the sister chromatids, chromatids (now called chromosomes) move to opposite poles

Question 10

What happens during telophase II of meiosis II?

Answer 10

Chromosomes decondense, nuclear membrane reforms, cells divide (cytokinesis) to form four haploid daughter cells

Question 11

Defien synapsis

Answer 11

In prophase I, homologous chromosomes undergo a process called synapsis, whereby they pair up to form a bivalent (or tetrad)

Question 12

Define chiasmata

Answer 12

The homologous chromosomes are held together at points called chiasmata (singular: chiasma)

Question 13

What are The three main sources of genetic variation arising from sexual reproduction?

Answer 13

Crossing over (in prophase I)
Random assortment of chromosomes (in metaphase I)
Random fusion of gametes from different parents

Question 14

Define non-disjunction

Answer 14

Non-disjunction refers to the chromosomes failing to separate correctly, resulting in gametes with one extra, or one missing, chromosome (aneuploidy)

Question 15

Define karyotyping

Answer 15

Karyotyping is the process by which chromosomes are organised and visualised for inspection

Question 16

What is chorionic villi sampling?

Answer 16

Chorionic villi sampling involves removing a sample of the chorionic villus (placental tissue) via a tube inserted through the cervix

Question 17

What is aminocentesis?

Answer 17

Amniocentesis involves the extraction of a small amount of amniotic fluid (contains fetal cells) with a needle

Question 18

What is the difference between mitosis and meiosis in terms of divisions?

Answer 18

Mitosis: one

Meiosis: two

Question 19

What is the difference between mitosis and meiosis in terms of independent assortment?

Answer 19

Mitosis: no

Meiosis: yes (metaphase I)

Question 20

What is the difference between mitosis and meiosis in terms of synapsis?

Answer 20

Mitosis: no

Meiosis: yes- form bivalents

Question 21

What is the difference between mitosis and meiosis in terms of crossing?

Answer 21

Mitosis: no

Meiosis: yes (prophase I)

Question 22

What is the difference between mitosis and meiosis in terms of outcome?

Answer 22

Mitosis: two cells

Meiosis: four cells

Question 23

What is the difference between mitosis and meiosis in terms of ploidy?

Answer 23

Mitosis: diploid

Meiosis: haploid

Question 24

What is the difference between mitosis and meiosis in terms of use?

Answer 24

Mitosis: body cells

Meiosis: sex cells (gametes)

Question 25

What is the difference between mitosis and meiosis in terms of genetics?

Answer 25

Mitosis: identical cells

Meiosis: variation

Question 26

Define polyploidy

Answer 26

Polyploidy is a condition whereby an organism has more than two complete sets of chromosomes in all cells