Reproductive system 1

Question 1

What is the benefit and disadvantage of asexual reproduction?

Answer 1

primary form of reproduction for multiple species - may have short term benefits where population growth is critical BUT does not allow directly for genetic diversity, something very useful for adaptation to changing environments

Question 2

What are gametes?

Answer 2

Half the genetic information is carried in the gametes from each gender, so when combined, form the full genetic complement

Question 3

State the theory of homunculus?

Answer 3

The gametes (egg OR sperm) contained a complete preformed individual called a homunculus. Development was therefore a matter of enlarging this into a fully formed being.

Any maternal characteristics in the offspring attributed to the influence of the egg and gestation.

Question 4

What is the fate of the mesoderm?

Answer 4

From gastrulating embryo -> end up with mesoderm -> that forms part of kidney and gonadal somatic tissues.

Question 5

Where is the urogenital system derived from? Which place, are neural tube, notochord, somites, gonads and kidney derived from?

Answer 5

Urogenital system is derived from intermediate mesodermal type.
Neural tube is ectodermally derived.
Notochord is mesodermally derived.
Paraxial mesoderm form the somites.
Intermediate mesoderm forms gonads and kidneys.

Question 6

Compare developmental pathway of gonads in male and females.

Answer 6

The gonads in both male and female embryos follow a common developmental pathway. These develop from the common source; the genital ridge.

Question 7

Do the germ cells developing have a separate identity?

Answer 7

The germ cells, developing separately, also considered to have no intrinsic gender identity!

Question 8

What type of chromosomes do males and females have? What is their function?

Answer 8

In males:
There is Y chromosome, that carries SRY gene; master regulator of testis developments.

In females:
2X chromosomes; to drive ovarian development.

Question 9

Compare the fate of female and male cells for sex determination.

Answer 9

SRY master transcriptional regulator on Y chromosome drives formation of testis -> formation of sertollic cells -and leydig cells> these produce anti-mullerian hormone and testosterone.

In females,
Formation of ovarian structure -> formation of female ductal system, hormones from granulosa and theca cells (that produce female external genitalia and anatomy and physiology).

Question 10

Where are germs cells and Sertoli cells located in foetal testis?

Answer 10

Germ cells (gonacytes) cells on centre of cords. 
Sertoli cells around outside  of the structure.

Question 11

What is the indeterminate genital ridge accompanied by?

Answer 11

• Müllerian ducts (ultimately female)

- Wolffian ducts (ultimately male)

Question 12

Compare the different fate choices in males and female embryos.

Answer 12

Female:

- Wolfian ducts will degenerate 
- Leaving mullerian ducts -> that develop into fallopian tubes, uterus and vagina. 

Male:

- Wolfian ducts will develop into vas deferens, prostrate and seminal vesicles. 
- Mullerian ducts will degenerate under control of anti-Mullerian hormone -> which produces sertoli cells (somatic cells of testis that are switched on in SRY gene.

Question 13

Compare male and female reproductive anatomy at birth.

Answer 13

In males: Defined seminal vesicles, ejaculatory duct, prostrate vas deferens, testes.
In females: Uterine tubes, ovaries, fallopian tubes, uterus and vagina.

Question 14

Compare development of external genitalia in males and females.

Answer 14

Male:

- Urethral fold start to come around and enclose urethra -> to form glans penis and penis. 
- Labioscrotal swellings will become scrotum. 
- Testis will descend from abdomen (where they develop) -> to front of pelvis -> to scrotum. 

In female:

- There is glans clitoris, not glans penis (like males)
- Urethral folds which become labia majora. 
- Urethra remains open.

Question 15

Are the clitoris and penis homologous tissues?

Answer 15

The clitoris and penis are homologous tissues i.e. they develop from the same tissues and their underlying structure (and function?) is very similar.

Question 16

What are some of the fundamental similarities that remain in male and female reproductive systems?

Answer 16

Circumscribed anteriorly by the pubic symphysis, laterally by the ischial tuberosities, and posteriorly by the coccyx
• Urogenital (anterior) triangle – Contains the urethral and vaginal orifices in females and the base of the penis and the scrotum in males

Question 17

What is process of sex determination in males and females?

Answer 17

Start with SRY master transcription factor -> this produces SRY protein -> produces testis -> support the formation of testis.
Testosterone from Leydig cells, anti-Mullerian hormone from Sertoli cells to regress Mullerian ducts -> production of male genetalia, external sex characteristics and adult phenotype from testosterone.

Question 18

What is process of sex determination in males and females?

Answer 18

Males: Start with SRY master transcription factor -> this produces SRY protein -> produces testis -> support the formation of testis.
Testosterone from Leydig cells, anti-Mullerian hormone from Sertoli cells to regress Mullerian ducts -> production of male genetalia, external sex characteristics and adult phenotype from testosterone.

Females:
Two X chromosomes combine together to support development of ovary -> hormones produced by ovary will produce female genitalia and female external sex characteristics -> oestradiol and progesterone -> adult phenotype.

Question 19

What happens when sexually dimorphic development is disrupted in males and females?

Answer 19

XY females: if SRY gene is disrupted in some way.
XX male: Within genome, there’ll be enough of Y chromosome to contain that SRY gene that will start off cascade that leads to testis development.

Question 20

What are the characteristic of Swyer syndrome?

Answer 20

• Phenotypically female (external) -
  
  • Due to only 1 X chromosome, streak ovaries (increased likelihood of cancer) -
  • no post-pubertal development of 2 degree sex characteristics (lack of hormone production) - no germ cells. If streak ovaries produce enough of hormonal signals to produce a uterus, she may be able to carry a child.

Question 21

What are the characteristics of androgen insensitivity syndrome?

Answer 21

Genetic sex: XY
• Phenotypic/Psychosocial sex: Female
• Normal to high testosterone circulates, but cannot bind to cytoplasmic receptors – hence ‘insensitive’ to testosterone during development

Question 22

Do these women have internal testes? Can their body cells respond to it? Why is there a large breast development in females with a lot of testes?

Answer 22

• They have internal testes.
  
  • None of body cells can response to testosterone.
  • High levels of testosterone is converted to oestrogen to drive secondary sexual characteristics (breast formation) in androgen insensitivity syndrome.

Question 23

What is endometriosis?

Answer 23

Endometriosis: a condition resulting from the appearance of endometrial tissue outside the uterus and causing pelvic pain, especially associated with menstruation.

Question 24

What are two fundamental cell types?

Answer 24

Somatic and germ cells.

Question 25

Can germ cells undergo both meiosis and mitosis, or just one?

Answer 25

Both

Question 26

Are germ cells immortal?

Answer 26

Since germ cells go on to next generation, they are immortal.

Question 27

Which cells can germ cells give rise to?

Answer 27

Germ cells can make all cell types in body (nerve cells, blood and muscle).

Question 28

How is the germline separated from somatic lineages.

Answer 28

When embryo develops, it goes through zygote stage -> blastocyst stage, and gets through gastrulation.

Rest of the somatic cells of the body develop from ectoderm, mesoderm and endoderm. But, germ cells go to a different lineage.

Question 29

What do germ cells have to be protected from?

Answer 29

Germ cells have to be protected from all differentiation signals that other somatic cells of the body are experiencing, and responding because germline needs to retain mutation its pluripotency.

Question 30

Describe the stages in primordial germ cell journey in mouse.

Answer 30

Specification: Around 6 cells in the mouse embryo express Blimp1 (E5.5-6.5)

Commitment: After proliferation, a subset of the Blimp1 positive cells express Stella, and commit to the germline

Migration: PGCs undergo both passive and active migration to the gonads. Extensive proliferation occurs during this migration

Colonisation:
If germ cells find themselves in females embryo, ovary will already have started to develop. As germ cells enter ovary -> they are oogonia -> they undergo meiosis -> stop at prophase 1 of meiosis until puberty.

If germ cells are in male embryo, it would have developed into testes. Germ cells colonise testes, then they are known as gonocytes. They don’t enter meiosis at all, but undergo mitosis -> stop -> enter mitosis again in birth -> they don’t enter meiosis until puberty.

Question 31

What are the stages in primordial germ cell journey - human

Answer 31

Specification and commitment: Little is known of the earliest stages of human germ cell development, but embryonic stem cell approaches are now allowing this period of development to be investigated

Migration: During the fourth week of human gestation, PGCs migrate from the yolk sac and into the developing embryo. Extensive proliferation occurs during the journey.

Colonisation:
Female: If they enter into an ovary, they differentiate into oogonia and resting prophase one of meiosis by week 12.

Male: male germs cells enter gonads from gonacytes. At birth, these become followed by intermediate spermatogonia and prespermatogonia. They won’t enter into meiosis.

Question 32

What happens when there are tumours of male germline?

Answer 32

Gonocytes will reach gonad, arrest in germ cell differentiation, and become resistance to all the differentiation cues they would respond to -> become spermatogonium and produce sperm -> they form carcinoma in situ tubules (carcinoma are embryonic cells that sit there and are resistant to any kind of differentiation, all the way through childhood, and into puberty stages, where hormonal and and structural changes in testis lead to development of seminoma or non-seminoma.

Question 33

Compare the sperm counts in species that male with a single male, and species that copulate with multiple males.

Answer 33

Species where females mate with a single male (i.e., monogamy, polygyny, or dispersed)
sperm counts low
eg seahorses, pipefish – female deposits eggs in male brood pouch for fertilisation
no competition = sperm count almost undetectable.

In contrast, in species where females copulate with multiple males
sperm counts high
eg Bonobos, Australian fairy-wren
- male wren produces 8.3 billion sperm/ejaculate

Question 34

What are some factors that affect reproduction?

Answer 34

Behavioural: social structures (eg marriage, lion pride) seductory or dominance behaviours precopulatory and postcopulatory mate-guarding occurs in birds, lizards, insects and primates.

Physical 
external physical attributes as reproductive signals 
more/faster/”better” sperm 
removing the sperm of the competition* 
copulatory plugs 
leaving body parts behind

Morphological
shape of the penis
copulatory movement

Question 35

Compare the relationship between frequency of multiple mating by females and male testis size

Answer 35

ANS in slides

Question 36

What is the relationship between sperm swimming speeds and fertilisation.

Answer 36

Female chimps and macaques typically mate with several males in a social group, so that a male with faster and stronger swimming sperm cells would in theory be more likely to successfully fertilize an egg.

Have a look boxplot in slides.

Question 37

What are some strategies of reproductive wars (so like fertilising faster, or competing for fertilisation with another male)?

Answer 37

Sperm cooperation: Sperm can bundle together to form a group of sperm from same individual. They all swim together and end up getting to egg faster than a single sperm would

Sperm competition: Destruction of sperm from prior partners reduction of female mating instincts

Prolonged copulation: If you’re there with the female, your competitor cannot mate with that female.

Question 38

Examples of termination the fertilisation success of previous male.

Answer 38

Frequently observed in insects, reptiles, some mammals, and spiders - physically blocking the transfer of sperm. They leave a plug or barrier behind in the female so nobody can get in and deposit their sperm that will get to an egg.

ALSO Drosophila and Bumblebee seminal fluid contains “anti-aphrodisiac.” Once females are exposed anti-aphrodisiac and she loses interest in mating with any other male.

Drosophila seminal fluid contains pheromones and modified enzymes that destroy the sperm already in the female reproductive tract. If male is coming along second, they can come in and aspects of their sperm would destroy any sperm that is already there.

In some insects and spiders, the male copulatory organ breaks off or tears off at the end of copulation within the female. Male copulatory organ breaks off inside the female after copulation and remains there as a barrier to any further copulation. It ensures that their sperm is the only one that has the potential to reach the egg.

Prolonged copulation. If you stay, there are no other male there.