Meiosis

Question 1

What happens in the process of Meiosis I?

Answer 1

Diploid cell become haploid (reductive division)
- Homologous chromosomes become separated

Question 2

Name all cells involved in spermatogenesis?

Answer 2

• Spermatogonium
• Primary spermatocyte
• Secondary spermatocyte
• Spermatid
• Spermatozoa

Question 3

What do spermatagonium undertake to become primary spermatocytes?

Answer 3

Mitosis

Question 4

What do primary spermatocytes undergo to become secondary spermatocytes?

Answer 4

Meiosis I

Question 5

What do secondary spermatocytes undergo to become spermatids?

Answer 5

Meiosis II

Question 6

What so spermatids undergo to become spermatozoa?

Answer 6

Spermiogenesis

Question 7

What stage of meiosis are primary oocytes arrested in until puberty?

Answer 7

Prophase of meiosis I

Question 8

After puberty what stage of meiosis are oocytes arrested in until fertilisation?

Answer 8

Metaphase of meiosis II

Question 9

What does the term aneuploidy mean?

Answer 9

An abnormal chromosome number (monosomy or trisomy)

Question 10

What is disomy?

Answer 10

2 copies of a chromosome (normal)

Question 11

What is monosomy?

Answer 11

1 copy of chromosome

Question 12

What is trisomy?

Answer 12

3 copies of chromosome

Question 13

What is meiotic nondisjunction?

Answer 13

Failure of chromosome pairs to separate

Question 14

When can meiotic nondisjunction occur?

Answer 14

Either in meiosis I or II

Question 15

If meiotic nondisjunction occurs in meiosis I how many chromosomes will the daughter cells have by Meiosis II?

Answer 15

There will be 2 diploid daughter cells (with mixture of maternal and paternal genes) and 2 cells w/o chromosomes

Question 16

Give an example of a syndrome with monosomy?

Answer 16

Turner syndrome (45X)

Question 17

What trisomys are compatible with life?

Answer 17

• Trisomy 21: Down syndrome
• Trisomy 18: Edward syndrome
• Trisomy 13: Patau syndrome

Question 18

What percentage of Down Syndrome is due to meiotic nondisjunction?

Answer 18

95%

Question 19

Why is it that it is most likely that it is through the mother that NDJ errors occur?

Answer 19

Because meiosis I is suspended for such a long time
- Also why advanced maternal age increases the chances of trisomy

Question 20

How can you differentiate between trisomy caused by NDJ in Meisosis I vs Meiosis II?

Answer 20

Meiosis I NDJ chromosomes will all be different
- Meiosis II NDJ - 2 chromosomes will be identical

Question 21

What is uniparental disomy?

Answer 21

When the child has 2 copies of 1 parent’s chromosomes

Question 22

What is uniparental disomy?

Answer 22

Child has 2 copies of 1 parent’s chromosomes
- No copies of other parent’s chromosomes

Question 23

What is isodisomy?

Answer 23

Uniparental disomy
- 2 copies of same chromosome (meiosis II error)

Question 24

What is heterodisomy?

Answer 24

Uniparental disomy
- Meiosis I error, chromosomes are different

Question 25

What is the phenotypical features of a child affected by uniparental disomy?

Answer 25

Usually has a normal phenotype - Can lead to phenotype of recessive disease

Question 26

How many chromosomes do children with uniparental disomy have?

Answer 26

Normal number of chromosomes - Child is 'euploid'

Question 27

What kind of chromosomes have robertsonian translocations?

Answer 27

Acrocentric chromosomes - Centromere near end (short short arm)

Question 28

What is robertsonian translocation?

Answer 28

Fusion of long arms of 2 chromosomes

Question 29

What chromosomes are acrocentric (centromere near end)?

Answer 29

13, 14, 21, 22

Question 30

What is a less common cause of down syndrome?

Answer 30

Robertsonian translocation

Question 31

What are the most common robertsonian translocations?

Answer 31

- 13-14 - 14-21

Question 32

What are the clinical consequences of people with a carrier robertsonian translocation?

Answer 32

- Many monosomy and trisomy gametes - Frequent spontaneous abortions - Carrier may have child with Down Syndrome (trisomy 21)

Question 33

Why are those with robertsonian translocations usually have a normal phenotype?

Answer 33

Only lose short arms

Question 34

How many chromosomes do people with a carrier robertsonian translocation have?

Answer 34

45 (one translocated)

Question 35

How can a robertsonian translocation be diagnosed?

Answer 35

Karyotyping