Meiosis

Question 1

What are two ways Meiosis creates genetic diversity?

Answer 1

Random assortment of chromosomes - 8 million possible combinations of 23 pairs of chromosomes

Recombination - increases diversity of gametes

Question 2

What are the key features of meiosis?

Answer 2

Two nuclear and cell divisions without an intervening S phase

Meiosis I - reduction in genetic material

Meiosis II - resembles mitosis

Question 3

Describe the nomenclature for chromosome number and DNA content

Answer 3

Chromosome number - designated by N, 1N = haploid, 2N = diploid

DNA content - Designated by C, a haploid nucleus contains 1C, a cell is 4C after S phase

Question 4

What is N and C at the end of Meiosis I?

Answer 4

1N, 2C

Homologous chromosomes segregate, hence 1N

Each chromosome still has 2 chromatids, hence 2C

Question 5

What are two key events that happen during Prophase I?

Answer 5

Pairing (synapsis) of homologous chromosomes via synaptonemal complex

Recombination

Question 6

What are the stages of Prophase I?

Answer 6

Leptotene

Zygotene

Pachytene

Diplotene

Diakinese

Defined by chromosome morphology

Question 7

Describe the Leptotene stage.

Answer 7

Individual chromosomes visible

Double-stranded breaks occur

Formation of axial elements of synaptonemal complex

Question 8

Describe the Zygotene stage

Answer 8

Synapsis begines

Formation of lateral elements of synaptonemal complex - keeps homologous chromosomes together, maintained through pachytene

Question 9

Describe the Synaptonemal Complex

Answer 9

Axial elements - later form lateral elements

Transverse elements - Zipper-like structure that holds complex together

Recombination nodules - contains proteins that mediate recombination, sites of recombination

Question 10

Describe the pachytene stage

Answer 10

Complete synapsis

Recombination is completed

Question 11

Describe the diplotene stage

Answer 11

SC disassembles

Chromosomes held together by chiasmata

Oocytes arrest at this stage until ovulation

Question 12

Describe Diakinesis

Answer 12

Aka prometaphase

Chromosomes fully condensed in preparation for metaphase I

Question 13

What is a chiasmata?

Answer 13

Points of attachment between homologs

Sites of recombination

Required for proper segregation of homologous chromsomes

Question 14

Where does recombination occur in the sex chromosomes?

Answer 14

Pseudoautosomal region

Question 15

What does unequal crossing over result in?

Answer 15

Gene deletion and Gene duplication

Question 16

What are the differences between male and female meiosis?

Answer 16

Males begin at puberty and continues throughout life
Females begin during fetal development, and stops at menopause

Unequal division of cytoplasm occurs during M1 and M2 causing the formation of 1 ovum and 2 polar bodies that do not divide

Question 17

At what points during meiosis is female oocyte meiosis regulated?

Answer 17

Diplotene

Metaphase II

Question 18

What is cytostatic factor?

Answer 18

Responsible for maintaining Cdk1 in female meiosis I and arresting the process

Question 19

What is Mos?

Answer 19

Syntesized in oocytes following meiosis I, signals a pathway that inhibits APC/c

Fertilization inhibits this pathway at Emi2/Erp1 and activates APC/C