Reproduction Lectures for Exam 1

Question 1

Advantage of Sexual Reproduction?

Answer 1

Allows genetic information from two individuals to be combined in random and novel ways with each new generation, offering the further advantage of introducing variability into a population.

Question 2

Germ Cells, where are they formed?

Answer 2

Germ cells also known as gametes, Sperm and Ova. Formed in Gonads, Testes and Ovaries.

Question 3

Meiosis is what type of division?

Answer 3

Reduction Division (from 2n to n)

Question 4

How many chromosome do normal cells have? How many do gametes have?

Answer 4

Regular cells are Diploid- 46 chromosomes (23 pairs of homologous chromosomes)
Gametes- Haploid, 23 chromosomes.

Question 5

Growth of a zygote into an adult member of the next generation occurs via what division?

Answer 5

Mitotic Cell division, duplicative division.

Question 6

Chromosome pairs 1-22 are called what?

Chromosome pair 23?

Answer 6

1-22- Autosomal Chromosomes

Pair 23- Sex Chromosomes, x or y. So unlike 1-22 these are not identical chromosomes and may not contain similar genes.

Question 7

Sex is determined by which chromosome?

Answer 7

Y Chromosome (has only ~80 genes) That means the Male determines the sex of the offspring.

Question 8

When meiosis occurs in the testes how do the XY and chromosomes undergo their own version of “recombination”

Answer 8

X and Y chromosome do not undergo recombination because they are not homologous. Instead only the tip of the X chromosome, which contains ~54 genes that are homologous in the X and Y, can recombine with the Y chromosome during meiosis.

Question 9

What is Euchromatin?

Answer 9

Euchromatin is the extended active form of DNA.

Question 10

What is the Y chromosome believed to have evolved from?

Answer 10

The X chromosome, because it has includes X-transposed sequences almost identical to regions of the X chromosome, degenerate regions, and testis-specific genes.

Question 11

Most of the testis-specific genes expressed by spermatogenic cells were found to be located in what? and what does that mean?

Answer 11

Palindromes.
Palindromes are regions of DNA that read the same from either direction. (believed these substitute for crossing-over and help protect these important genes from genetic changes and conserve the genes over evolutionary time)

Question 12

Why are a woman’s cells said to be “mosaic”?

Answer 12

Each diploid cell in a woman’s body inherits two X chromosomes, but because of X chromosome inactivation only one is fully active while the other is inactive. The inactivation is random so from cell to cell you could have an active X chromosome that may be derived from either parent.

Question 13

Barr Body

Answer 13

Inactive X Chromosome in a female that forms a clump of heterochromatin, looks like a dark spot.

Question 14

Two sets of autosomal chromosomes also have two what?

Answer 14

Two alleles (forms) of each gene on the chromosomes/ (most cases both are expressed, but in some cases either the maternal or the paternal allele is silenced)

Question 15

During the first 40 or so days of development, after conception, the gonads of males and females are similar in appearance. What is the name of the cell that will later give rise to either sperm or ova, and where does it migrate from?

Answer 15

Primordial germ cells, they migrate from the yolk sac to the developing embryonic gonads.

Question 16

What has to be present to promote the conversion of non-determined gonads to testes? And what is the name of the gene?

Answer 16

The Testis-Determining Factor (TDF), which is located on the short arm of the y chromosome.
SRY gene (Sex Determining Region of Y).

Question 17

What must be absent for pathways directed by the X chromosome to result in the development of ovaries?

Answer 17

The Y chromosome must be absent, there cannot be any TDF or SRY gene present.

Question 18

How would you have a male baby with XX genotype? Or a female baby with XY?

Answer 18

For a male baby to have male gonads and be XX, one of the X chromosomes must have contained a segment of the Y chromosome (resulted from an error in meiotic division)
For a female baby to have female gonads and be XY, the y chromosome must have been missing the portion of the y chromosome that would normally lead to formation of testes, TDF and SRY gene.

Question 19

When do Seminiferous Tubules appear in embryonic development? What two cells are found there?

Answer 19

Seminiferous Tubules appear at ~ day 43- day 50.

Contain Germinal and Non-Germinal Cells.

Question 20

What Cells will eventually arise from the germinal and non-germinal cells found in seminiferous tubules?

Answer 20

Germinal- Eventually become Sperm

Non-Germinal- Eventually become Nurse cells, also called Sertoli cells, or Sustentacular cells (around day 42)

Question 21

Two other names for Sertoli cells?

Answer 21

Nurse Cells, Sustentacular Cells

Question 22

What begins to appear in male embryonic tissue around day 65?

Answer 22

Leydig cells, also called interstitial endocrine cells.

Question 23

Where are Leydig cells found?

Answer 23

They are clustered in the interstitial tissues that surrounds the seminiferous tubules.

Question 24

Another name for Interstitial Endocrine Cells?

Answer 24

Leydig Cells

Question 25

What are Leydig cells responsible for secreting in the embryonic testes?

Answer 25

Large amounts of male sex hormones (Androgens) The major androgen being Testosterone.

Question 26

Testosterone secretion beings as early as when? When does it peak? What is the rest of it’s cycle like until puberty?

Answer 26

Testosterone secretion begins as early as 8 weeks after conception, reaches a peak at 12-14 weeks, and then declines to very low levels by the end of the second trimester (~21 weeks). Testosterone levels rise again in newborn boys until 3 months and then fall to almost undetectable levels by ages 7-12 months, levels are basically the same between sexes until adolescence.

Question 27

As the testes develop where do they move to? What is it called when they don’t descend?

Answer 27

As the testes develop they move within the abdominal cavity and gradually descend to the scrotum, sometimes that doesn’t finish until shortly after birth.
If they don’t descend it is called Cryptorchidism.

Question 28

Why do the testes have to be in the scrotum for spermatogenesis?

Answer 28

Spermatogenesis requires cooler temperatures, usual kept around 35 degree C, about 3 degrees lower than the body temp.

Question 29

When do the functional unit of the ovaries- the ovarian follicles begin developing?

Answer 29

Not until the second trimester of pregnancy, ~day 105.

Much slower than the rapid development of testes in the beginning of pregnancy.

Question 30

Most internal accessory sex organs are derived from two systems of embryonic ducts. What are they?

Answer 30

Male accessory organs- Wolffian (Mesonephric) Ducts

Female accessory organs- Mullerian (paramesonephric) Ducts.