Meiosis and Mitosis

Question 1

Look at the diagram of the testis

Answer 1

..

Question 2

Spermatogenesis the hormones

Answer 2

• Hypothalamus secretes GnRH
• this stimulates the A.pit to secrete FSH and LH
• in the testes then…
• the leydig cells secrete testosterone
• and the sertoli cells carry out spermatogenesis

Question 3

Meiosis- Prophase I

Answer 3

Homologus chromosomes appear, each made of 2 chromatids joined at the centromere

Question 4

Meiosis- Metaphase I

Answer 4

Spindle forms and homologous pairs of chromosomes line up on the metaphase plane

Question 5

Meiosis- Anaphase I

Answer 5

No centromere split, homologous pairs are pulled to opposite ends of the cell

Question 6

Meiosis- Telophase I

Answer 6

Nuclear membrane reforms around the 2 haploid nuclei

Question 7

Meiosis - Prophase II

Answer 7

• nuclear membrane starts to break down again
• the chromatids are still joined by the centromeres
• no DNA replication, no crossing over

Question 8

Meiosis - Metaphase II

Answer 8

New spindles form and pairs of chromatids line up on metaphase plane

Question 9

Meiosis - Anaphase II

Answer 9

Centromeres divide and the chromatids are pulled to opposite ends of the cell

Question 10

Meiosis - Telophase II

Answer 10

nuclear envelope reforms and chromosomes uncondensed giving 4 haploid nuclei
-once the nuclear division is complete cytogenesis completes the division process to give 4 haploid nuclei

Question 11

Mitosis- Interphase

Answer 11

Chromosomes duplicate, the copies remain attached to one another

Question 12

Mitosis - Prophase

Answer 12

in the nucleus the chromosomes condense and become visible

spindle forms in the cytoplasm

Question 13

when does the nuclear envelope break down during mitosis?

Answer 13

prophase, after the chromosomes have condensed

Question 14

Mitosis - Metaphase

Answer 14

the chromosomes are aligned in the middle of the spindle

Question 15

Mitosis - Anaphase

Answer 15

Chromosomes separate into 2 genetically identical groups and move to opposite ends of the spindle

Question 16

Mitosis - Telophase

Answer 16

Nuclear membranes form around the 2 sets of chromosomes which then begin to spread out and the spindle begins to break down.

Question 17

how many pairs of chromosomes do humans have?

Answer 17

23 pairs

Question 18

when does crossing over occur in meiosis?

Answer 18

Prophase I

Question 19

Spermatogenesis

Answer 19

• Primordial germ cell
• enters testes - spermatogonia
• spermatogonia proliferate by mitts division inside testis
• primary spermatocyte
• meitotic division I
• secondary spermatocytes
• meitotis division II
• Spermatids. differentiate into mature sperm

Question 20

How long does it take to produce a mature germ cell?

Answer 20

75 days

and 21 days to transport that sperm to the t sack bit

Question 21

How do low levels of FSH affect spermatogenisis

Answer 21

sperm levels can continue

Question 22

How do low levels of testosterone affect spermatogenesis?

Answer 22

required absolutely for spermatogenesis

Question 23

what does androgen binding protein do during spermatogenesis?

Answer 23

• produced by the sertoli cells

- ensures that the concentration of testosterone in the testes is high enough to maintain spermatogenesis.

Question 24

what does mitosis produce?

Answer 24

2 identical daughter cells - diploid

Question 25

what does meiosis produce?

Answer 25

1/2 the number of chromosomes as parent cell, 4 daughter cells that are halpoid

Question 26

in spermatogenesis where does the genetic variation happen?

Answer 26

prophase I, pro metaphase I

Question 27

during spermatogenesis what are the spermatids formed from?

Answer 27

secondary spermatocytes

Question 28

when are secondary spermatocytes produced?

Answer 28

meiosis II

-divide to produce haploid spermatids

Question 29

what is spermiogensis?

Answer 29

spermatids begging to grow a tail and develop a thickened meat pies where mitochondria gather and form an axoneme

Question 30

what packages spermatid DNA?

Answer 30

nuclear basic proteins, replaced with protamines during spermatid elongation… results in a tightly packed chromatin which is inactive

Question 31

Where are non motile spermatozoa transported to ?

Answer 31

epidermis in the testicular fluid secreted by sertoli cells aided by peristaltic contraction