Gametogenesis & Cell division

Question 1

What is an autosome?

Answer 1

A non-sex chromosome

Question 2

How many chromosomes are there in a normal somatic cell?

Answer 2

46 (22 pairs of autosomes and 2 sex chromosomes)

Question 3

What is mitosis?

Answer 3

Diploid 2N cell replicates it’s DNA to form a diploid 4N cell and divides to form two identical 2N daughter cells

Question 4

What is meiosis?

Answer 4

Diploid 2N cell replicates it’s DNA to form a 4N diploid cell which undergoes two cell divisions (meiosis 1 and 2) to form 4 haploid 1N cells (gamete)

Question 5

In males, how many spermatozoa are produced from meiosis of 1 germ cell?

Answer 5

4 spermatozoa (4 haploid cells)

Question 6

In females, how many oocytes are yielded from a single germ cell?

Answer 6

1 haploid oocyte with 3 non functional, small haploid polar bodies

Question 7

What are the phases of interphase?

Answer 7

G1, synthesis, G2

Question 8

What are the phases of m phase?

Answer 8

Mitosis and cytokenesis

Question 9

What are the phases of mitosis?

Answer 9

Prophase, métaphase, anaphase, telophase

Question 10

What happens in prophase?

Answer 10

Chromosomes condense, nuclear envelop dissolves, miroirs spindle fibers form

Question 11

What happens in metaphase?

Answer 11

Chromosomes align at the equator of the cell

Question 12

What happens in anaphase?

Answer 12

The chromosomes split to opposite poles of the cell

Question 13

What happens in telophase?

Answer 13

Last phase of mitosis, the nuclear envelope forms around the chromosomes in preparation for cytokenesis

Question 14

When do primordial germ cells form?

Answer 14

By the 2nd week of gestation

Question 15

Where do primordial germ cells form?

Answer 15

In the yolk sac by the 2nd week

Question 16

What are primordial germ cells?

Answer 16

The cells which go on to develop into gametes

Question 17

What is the role of somatic support cells in the formation of female genitalia?

Answer 17

They form the ovarian follicle cells

Question 18

What is the role of somatic support cells in the formation of male genitalia?

Answer 18

They form the testis cords and eventually the Sertoli cells of the seminiferous tubules

Question 19

What are primordial germ cells called in females once they have been surrounded by the somatic support cells of the ovaries?

Answer 19

Oogonia

Question 20

What are oogonia?

Answer 20

Female primordial germ cells (diploid cells)

Question 21

What do oogonia become?

Answer 21

Primary oocytes (when they start to undergo meiosis)

Question 22

What are primary oocytes?

Answer 22

An oogonia which has started to undergo meiosis. Meiosis is arrested in prophase 1 in diplotene phase until puberty

Question 23

What do primary oocytes become?

Answer 23

Secondary oocytes (oocytes entering the second phase of meiosis)

Question 24

When do primary oocytes mature into secondary oocytes?

Answer 24

At puberty

Question 25

When does the secondary oocyte complete meiosis?

Answer 25

After it the egg has been ovulated and fertilised

Question 26

How many eggs are present at birth?

Answer 26

1-2 million

Question 27

How many eggs are present at puberty?

Answer 27

300,000

Question 28

How many eggs are present in a 20 week female fetus?

Answer 28

6-7 million (they degenerate from this point onwards

Question 29

Which gene determines whether a primordial germ cell will differentiate into an egg or a sperm?

Answer 29

SRY gene on the Y xsome, if present the cells will turn into male gametes

Question 30

What is a primordial follicle?

Answer 30

A female gamete surrounded by a thin layer of granulosa cells and an external basal lamina

Question 31

What is a primary follicle?

Answer 31

A gamete surrounded by a thick layer of granulosa cells and a basal lamina

Question 32

Which layer of the follicle is vascular?

Answer 32

The inner thecal layer

Question 33

GAMETOGENESIS

Answer 33

Maturation (formation) of Germ cells into Gametes | is called Gametogenesis.

Question 34

Germ cells

Answer 34

are those which change into gametes | Sperm & Ovum

Question 35

what are germ cells ?

Answer 35

( oogonium , spermetogonium , primary | oocytes and primary spermatocytes ).

Question 36

Gametes

Answer 36

Sperms and Ova contains (23 haploid) | chromosome

Question 37

How many chromosomes in germ cells ?

Answer 37

contains 46 No of chromosomes. (diploid)

Question 38

Describe G1 phase ?

Answer 38

- characterized by resumption of bio- synthesis - growth and production of protiens for DNA synthesis - duration is highly variable

Question 39

Describe S phase?

Answer 39

- amount of DNA effectively doubled -> cell replicates its DNA - Each chromosome replicated -> sister chromatids

Question 40

Describe G2 phase?

Answer 40

Growth and final preparations for cell divsion

Question 41

• Differentiation of the | PGCs begins in the ________

Answer 41

the ovary. In the uterine | life of female fetus

Question 42

• By the third month | of development Few of the _______ start their Meiosis.

Answer 42

Primary Oocytes

Question 43

• Mitotic division | takes place in _________ until the primary spermatocytes.

Answer 43

GERM CELLS

Question 44

Describe changes that Spermatids go through?

Answer 44

1. Formation of acrosome 2. Condensation of nucleus 3. Formation of neck, middle piece and tail 4. Shading of most of cytoplasm

Question 45

Abnormal Gamete

Answer 45

``` • During meiosis, homologous chromosomes sometimes fail to separate and go to opposite poles of the germ cell • As a result of this error of meiotic cell division (nondisjunction) some gametes have 24 chromosomes and others only 22 ```

Question 46

Trisomy

Answer 46

``` • If a gamete with 24 chromosomes unites with a normal one with 23 chromosomes during fertilization • A zygote with 47 chromosomes forms • This condition is called trisomy ```

Question 47

Monosomy

Answer 47

• If a gamete with only 22 chromosomes unites with a normal one, a zygote with 45 chromosomes forms • The condition is called monosomy