Lecture 2 - What is Sexual Reproduction?

Question 1

What are the four ADVANTAGES of sexual reproduction?

Answer 1

1. The way genetic material is recombines allows for genetic variation & evolutionary flexibility
2. “bet-hedging” for maximising a population’s survival
3. “Hybrid vigour” against diseases & parasites
4. Allows for a rapid response to changes in environmental conditions

Question 2

What is the main DISADVANTAGE of sexual reproduction?

Answer 2

Both sexes must be present - can’t have a female-only population

Question 3

What is one way species have adapted to the one disadvantage of sexual reproduction?

Answer 3

Pathenogenesis e.g. fish, amphibians and lizards. When a female can reproduce either sexually or asexually.

Question 4

Define GYNOGENESIS.

Answer 4

Female produces eggs with the full complement of chromosomes but relies on sperm (any sperm) contact to develop

Question 5

Define HYBRIDOGENESIS.

Answer 5

Female produces eggs which are fertilised by a male from a closely related species, however only the maternal genetic material is passed on in the gametes.

Question 6

Name for the an egg which is fertilised by sperm?

Answer 6

Zygote

Question 7

What is an ANAMNIOTE?

Answer 7

The developing embryos do not have an amniotic membrane, these include all fish and amphibians.

Question 8

What is an AMNIOTE?

Answer 8

The developing embryos have an amniotic membrane, these include all reptiles, birds and mammals.

Question 9

In anamniotes fertilisation occurs (1) the body, In amniotes it occurs (2) the body.

Answer 9

(1) Outside

(2) Inside

Question 10

What is the role of the cleidoic egg?

Answer 10

It allows amniotes to bypass the aquatic larval stage.
Allows for the formation of other extra embryonic membranes.
Allows for gas exchange.

Question 11

How has environmental conditions affected reproduction for animals?

Answer 11

• Protection against desiccation (removalof water from something that is normally kept moist): egg shell formations in birds and reptile
• Internal incubation of the developing embryo in most mammals and some reptiles, fish and amphibians
• Oviparity vs. viviparity

Question 12

What is an OVIPOROUS animal?

Answer 12

One that lays eggs only - birds, most fishes, amphibians and reptiles

Question 13

What is a VIVIPOROUS animal?

Answer 13

One that gives birth to live young - cartilagenous fishes (eg sharks), some teleost fish, a few amphibians, some reptiles, most mammals.

Question 14

What is the difference between OVIVIPARITY and VIVIPARITY?

Answer 14

O: where embryo develops inside the mother but does not rely on her to provide nourishment. Sometimes called aplacental viviparity. Where they pop out an independent, mature baby e.g. sharks. Can rely on a placenta, can also not.
V: embryo develops inside the mother with dependence on the mother for nutrient transfer. Sometimes called placental viviparity. Developing embryo is attached to the mother e.g. most mammals

Question 15

How do vertebrates maintain the separate sexes needed for genetic recombination in the new zygote?

Answer 15

1. Genotypic sex determination

2. Environmental sex determination

Question 16

What is GENOTOPIC SEX DETERMINATION?

Answer 16

• Males and females have a different chromosomal karyotype because they have different sex chromosomes
• Promotes the formation of separate sex-specific reproductive tracts

Question 17

What are the genotypes for male and female: mammals, birds, snakes, lizards & fish?

Answer 17

• Female mammal = XX (homogamety)
• Male mammal = XY (heterogamety)
• Female bird = ZZ
• Male bird = ZW
• Female snake = ZZ
• Male snake = ZW
• Male & female lizard = uses either XY, ZW or environmental determination system
• Male & female fish = uses a single gene system, multifactorial gene system or environmental determination system

Question 18

What is the sex determining region on the chromosome in mammals? In birds?

Answer 18

M: SRY on Y chromosome
B: DRMT1

Question 19

What is DOSAGE COMPENSATION?

Answer 19

Males only have one X chromosome
With the females one of the X chromosomes is seen as superfluous (unnecessary) to development so it is switched off very early on - this is random

Question 20

Is the Y chromosome getting shorter? If so, why?

Answer 20

• Male-specific region of the Y chromosome (MSY) accumulates single nucleotide polymorphisms more rapidly than have other chromosomes.
• Y-chromosomes of great apes have lost most of the genetic material except genes of MSY.

Question 21

What is a PROTOGYNOUS fish?

Answer 21

One that is female first and male second (undergoes a sex change during its life)

Question 22

What is a PROTANDROUS fish?

Answer 22

One that is male first and female second (undergoes a sex change during its life)

Question 23

What does the expression of aromatase CYP19a1a do?

Answer 23

• Converts androgens into oestrogens within the developing gonads
• This oestrogen production results in ovarian development

Question 24

What is one example of environmental sex determination?

Answer 24

Temperature Dependent Sex Determination (TSD)

Question 25

What mechanism is thought to cause environmental sex determination?

Answer 25

• Female-producing temperatures induce expression of the aromatase CYP19a1a, which converts androgens into oestrogens within the developing gonads
• e.g. Crocodiles: 29-31 degrees = 100% female, 32-34 degrees = 100% male
• Also believed other enzymes or steroid receptors may be involved coming from the yolk sac

Question 26

What are the three methods thought to have developed to overcome potential species catastrophe?

Answer 26

1. PATHENOGENESIS
2. GYNOGENESIS
3. HYBRIDOGENESIS