Meiosis

Question 1

What is a somatic cell?

Answer 1

Any cell that isn’t a part of the reproductive cells.

Question 2

What is the role of germ cells?

Answer 2

They are used to produce gametes which contain half the number of chromosomes as a somatic cell. Germ cells undergo meiosis to grow and divide into gametes.

Question 3

Where are germ cells found in the human body?

Answer 3

In males, the testes.

In females, the ovaries.

Question 4

What is the difference between sister and nonsister chromatids?

Answer 4

Sister chromatids belong to the same copy of the chromosome.

Nonsister chromatids refers to either of the two chromatids of paired homologous chromosomes,

Question 5

What is general overview of meiosis?

Answer 5

• DNA replication results in 2 homologous pairs
• First division separates homologous pairs into two cells
• Second division results in 4 haploid cells with 2 chromosomes after separation of sister chromatids

Question 6

What is the major difference between meiosis in males and females (humans)?

Answer 6

From puberty onwards, meiosis continues throughout the lives of males. A single meiotic divsion results in four haploid cells that are ready tovfertilize an ovum.

The products from a single meiotic division in females only gives a 1/4 as gametes.

Question 7

What are the two stages in the life cycle of a plant called?

Answer 7

• Gametophyte (gametes are produced)
• Sporophyte (haploid spores produced by meiosis)

Question 8

What typically happens in meiosis I?

Answer 8

Reductional division

Homologous chromosomes pair, exchange pair, exchange parts and segregate.

Question 9

What typically happens in meiosis II?

Answer 9

Behaves similar to mitosis. Divides sister chromatids into four daughter cells with just one chromosome. (Haploid)

Question 10

What is it called when two homologous pairs wind together to exchange genetic material?

Answer 10

Synapsis. This is unique to meiosis.

Question 11

What typically occurs at Prophase I?

Answer 11

Condensation of chromatin, homologous pairing. Genetic exchange.

Question 12

In human females what stage is meiosis suspended?

Answer 12

At prophase until ovulation.

Frokm ovulation it proceeds to metaphase 2 until fertilization.

Question 13

How many stages are involved in prophase 1?

Answer 13

5 stages. This follows as:

1. Leptotene
2. Zygotene
3. Pachytene
4. Diplotene
5. Diakinesis

Question 14

What is the mnemonic that helps to remember these stages?

Answer 14

LZPDD

Lonely Zombies Peel Delicious Doughnuts

Question 15

What is characteristic of zygotene?

Answer 15

• Synapsis occurs
• Chromsomes form a bivalent with a protein called synaptonemal complex

Question 16

What happens during pachytene?

Answer 16

• Synapsis fully occurs
• Recombination nodules allow genetic exchange between the maternal and paternal homologous pairs

Question 17

What part of the prophase 1 causes genetic diversity to greatly increase?

Answer 17

Crossing over of genetic information between maternal and paternal chromosomes.

Question 18

Describe what is seen during diplotene?

Answer 18

• Synaptonemal complex dissolves, However, chromosomes still keep condensing
• Homologous chromosomes start to move apart but remain tightly joined at chiasmata – sites where crossing over occurred
• Meiotic arrest occurs in many species

Question 19

What allows diakinesis to be distinguished?

Answer 19

All four chromatids can be seen.

Nuclear envelope breaks down

Spindle fibres begin to form

Question 20

Is there any difference between metaphase 1 and in mitosis?

Answer 20

Only difference is that the homologous chromosomes are still attched at the end as chiasmata

Question 21

What occurs during anaphase?

Answer 21

Chiasmata dissolve

Homologous chromosomes separate to opposite poles by spindle fibres

Question 22

What occurs during interkinesis?

Answer 22

Cytokinesis around the chromosomes.

No DNA replication

Question 23

Difference between metaphase 2 in meiosis and mitosis?

Answer 23

–The number of chromosomes is half that in mitotic metaphase in the same species

–Sister chromatids are no longer identical thanks to crossing over in meiosis I.

Question 24

What contributes to the level of genetic diversity during meiosis?

Answer 24

Independent assortment of chromosomes during metaphase 1

Different mix of paternal and maternal chromosomes gives different combinations in the final stage (telophase 2)

Question 25

What happens in the event of non-disjunction?

Answer 25

Zygotes end up with one more or one less chromosome during fertilization.

Question 26

Non-disjunction in anaphase 2?

Answer 26

Only half the zygotes will be normally fertilized