Meiosis

Question 1

What are the basic differences in the alignment process of chromosomes in mitosis vs meiosis?

Answer 1

Mitosis
Homologous chromosomes line up at the metaphase plate independently

Meiosis I
Homologous chromosomes are paired at the metaphase plate

Question 2

Describe the structure of replicated chromosomes post chromosome replication

Answer 2

Replicated chromosomes align to form a bivalent - both (paternal and maternal) chromosomes run parallel

Question 3

What are chiasma?

Answer 3

A structure that forms between a pair of homologous chromosomes by crossover recombination and physically links the homologous chromosomes during meiosis

Question 4

When do chiasma develop?

Answer 4

In prophase I

Question 5

Why is recombination important?

Answer 5

Its an important source of genetic diversity

Question 6

What is a Holliday junction?

Answer 6

Deciding between Prague or Bilbao
Also
Holliday junctions provide a covalent link between recombining DNA molecules and need to be removed prior to chromosome segregation at mitosis. - A branched nucleic acid structure that contains four double-stranded arms joined together

Question 7

You should listen to the lecture and write some notes on pairing + recombination of sex chromosomes in males here

Answer 7

Ye

Question 8

What are the main two sources of genetic diversity?

Answer 8

Independent assortment of maternal and paternal homologs during meiosis I

Crossing-over during meiotic prophase I

Question 9

What is MPF?

Answer 9

Maturation promoting factor

Question 10

What things mediate meiosis?

Answer 10

Like many of the same molecules as mitosis

Question 11

What is one thing that may cause an issue with correct meiotic division?

Answer 11

lacking degradation of cohesion complexes

Question 12

What may occur in fertilisation following meiotic errors?

Answer 12

A meiotic I or II error may cause a trisomic zygote

Question 13

What is uniparental disomy?

Answer 13

When someone receives two copies of a chromosome from one parent and none from the other

Question 14

What uniparental disomy occurs after M1 error?

Answer 14

Uniparental heterodisomy

Question 15

What uniparental disomy occurs after M1 error?

Answer 15

Uniparental isodisomy

Question 16

What may occur from uniparental disomy?

Answer 16

Angelman and Prada-Willi Syndromes. Beckwith-Wiedemann syndrome.

Question 17

How long does each stage of spermatogenesis take?

Answer 17

Spermatogonium -> primary spermatocyte or additional spermatogonia - 16 days

Primary spermatocytes -> Secondary spermatocytes via first meiotic division - 24 days

Secondary spermatocytes to spermatids via second meiotic division - a few hours

Spermatids -> sperm - 24 days

Question 18

Describe when Meiosis I occurs in oogenesis

Answer 18

During fetal development meiosis 1 begins
After puberty, primary oocytes complete meiosis I, which produces a secondary oocyte and a first polar body that may or may not divide again

(2n Oogonium -> 2n Primary oocyte -> 1n first polar body + secondary oocyte)

Question 19

Describe when Meiosis II occurs in oogenesis

Answer 19

The secondary oocyte begins meiosis II
A secondary oocyte (and first polar body) is ovulated
After fertilisation, meiosis II resumes, the oocyte splits into an ovum and a second polar body

(Secondary oocyte is ovulated and fertilised and splits into 2nd polar body and n+n ovum which becomes 2n zygote)

Question 20

In where and when is there an arrest in gene division in fertilisation?

Answer 20

A long arrest at prophase 1 from second trimester to post birth

Question 21

Do chromosome cohesion defects underlie maternal age effect?

Answer 21

Kinda but it aint so simple, eg trisomy 16 rates increase sharply between 18-21