Lecture 15: Meiosis

Question 1

What is the only haploid cell in humans called?

Answer 1

gametes

Question 2

How many chromosomes does a haploid cell have?

Answer 2

23

Question 3

Why do haploid cells only have 23 chromosomes?

Answer 3

Because they will have 46 once they combine with another cell, to allow them to combine.

Question 4

In Meiosis I, are there haploid cells?

Answer 4

Yes, but with duplicated chromosomes.

Question 5

In Meiosis II, are there diploid cells?

Answer 5

No, there are haploid cells with unduplicated chromosomes.

Question 6

How many phases are there in Meiosis? (I or II) Name them.

Answer 6

• There are four phases in each meiosis

- Prophase I & II, Metaphase I & II, Anaphase I & II, Telophase and Cytokinesis I & II

Question 7

What is the Chiasmata?

Answer 7

The part of the chromosome that is crossing over.

Question 8

In what phase of Meiosis does crossover occur?

Answer 8

Prophase I

Question 9

What happens in Metaphase I?

Answer 9

The chromosomes form a metaphase plate and microtubules attach to the kinetochore in the centromere of a chromosome.

Question 10

What happens in Anaphase I?

Answer 10

Each pair of homologous chromosomes separate, sister chromatids remain attached.

Question 11

What happens in Telophase & Cytokinesis I?

Answer 11

A cleavage furrow forms and two haploid cells are created. Sister chromatids are still in tact.

Question 12

What is the difference between Meiosis I & II?

Answer 12

At the end of Meiosis II, the sister chromatid are separated, and the result is 4 haploid daughter cells containing unduplicated chromosomes. At then end of Meiosis I, the result is the sister chromatids are still in tact, and there are 2 haploid cells with duplicated chromosomes.

Question 13

What is a tetrad?

Answer 13

When homologous sister chromatids group together.

Question 14

What is the action of crossing over called?

Answer 14

Synapsis.

Question 15

What happens during synapsis?

Answer 15

DNA is exchanged between the two homologous chromosomes at the chiasma.

Question 16

What does the process of synapsis create?

Answer 16

They create infinite genetic possibilities.

Question 17

What are the differences between Mitosis and Meiosis?

Answer 17

After the chromosome duplication, the results are different.
-Mitosis: end with duplicated chromosomes.
-Meiosis: ends with homologous chromosome pairs.
After Anaphase & Telophase,
-Mitosis: daughter cells have 2n
-Meiosis I: haploid have 1n with duplicated chromosomes.
-Meiosis II: haploid 1n with unduplicated chromosomes.

Question 18

How many cell divisions are there in Meiosis?

Answer 18

2

Question 19

Does the synapsis of homologous chromosomes happen in Mitosis?

Answer 19

No, it happens in Prophase I in Meiosis I.

Question 20

What is the number of daughter cells in genetic composition in Mitosis & Meiosis?

Answer 20

• Mitosis: 2 daughter cells (diploid) and are genetically identical to the parent cell
• Meiosis: 4 haploid cells, containing half as many chromosomes as the parent cells, and genetically different from each other and the parent cells.

Question 21

What role does Meiosis play in the animal body?

Answer 21

it produces gametes and reduces the number of chromosomes by half and introduces genetic variability.

Question 22

What role does Mitosis play in the animal body?

Answer 22

They enable multicellular adults to arise from the zygote. They produce cells for growth, repair, and in some species, sexual reproduction.

Question 23

What are sex differences in Meiosis?

Answer 23

• Girls: result is one oocyte and three polar bodies.

- Boys: result is four sperm cells.

Question 24

When does spermatogenesis begin?

Answer 24

Puberty and continues indefinitely

Question 25

When does oogenesis begin?

Answer 25

During fetal development but pauses at Prophase I, and it resumes each menstrual cycle but does not actually finish, only happens when egg is fertilized.

Question 26

Where does spermatogenesis perform Mitosis?

Answer 26

Spermatogonia

Question 27

What are the cells called during different phases of Meiosis in spermatogenesis?

Answer 27

Before meiosis: Primary spermatocyte. After meiosis I: Secondary spermatocyte. After meiosis II: Spermatids.

Question 28

What needs to occur in order for a spermatozoa to be complete?

Answer 28

the spermatid needs to grow a tail to become a spermatozoa.

Question 29

Where does the maturation of the spermatozoa occur?

Answer 29

In the seminiferous tubules.

Question 30

How many types of cells support spermatogenesis and name them.

Answer 30

- Two types - Leydig (Interstitial) cells - Sertoli cells

Question 31

Where are the Leydig cells located and what do they do?

Answer 31

Located between seminiferous tubules and they produce a large amount of testosterone which stimulates spermatogenesis.

Question 32

Where are the Sertoli cells located and what do they do?

Answer 32

Located in the seminiferous tubules and they support growing spermatocyte, and help accumulate testosterone in the seminiferous tubules, removes unnecessary waste, and produce certain hormones to feed back to the brain about spermatogenesis.

Question 33

Where is spermatozoa stored?

Answer 33

In the epididymis.

Question 34

What pathway does spermatozoa go through to leave the body?

Answer 34

Start at the epididymis. When ejaculation occurs, they leave through the vas deferens, which merges into the urethra.

Question 35

How many glands contribute to the production of semen? name them.

Answer 35

Seminal vesicle, prostate gland and bulbourethral (Cowper's) gland

Question 36

Which gland produces 60% of the fluid in semen?

Answer 36

Seminal vesicle

Question 37

What is the purpose of the liquid in the seminal vesicles?

Answer 37

To help counter the destructive environment of the vagina, with fructose as fuel for the spermatozoa.

Question 38

What does the prostate gland produce and what is its purpose?

Answer 38

A fluid to help sperm survive the vagina, and also makes semen less thick to be able to swim more freely.

Question 39

What does the Cowper's Gland produce and what is its purpose?

Answer 39

A clear fluid prior to ejaculation to neutralize urine in the urethra.

Question 40

Is the spermatogenesis random?

Answer 40

No, the hypothalamus produces GnRH, which travels to the pituitary gland and activates it.

Question 41

What does the pituitary gland produce?

Answer 41

it produces FSH and LH which travels in the blood to the testes.

Question 42

What does LH cause?

Answer 42

it allows Leydig cells to produce testosterone.

Question 43

What does FSH cause?

Answer 43

causes Sertoli cells to clump testosterone together and to produce inhibin.

Question 44

List the general process of hormonal help in spermatogenesis.

Answer 44

- Hypothalamus -> GnRH -> pituitary gland -> FSH and LH -> blood - LH -> Leydig cells -> testosterone - FSH -> Sertoli cells -> clumped testosterone and inhibin - Inhibin and testosterone -> brain -> reduce production of GnRH