01 - Mammalian Sex Determination

Question 1

(Asexual reproduction: Vegetative)

1-3. What are the three forms?

Answer 1

1. budding
2. fission (binary/other)
3. fragmentation

Question 2

(Asexual reproduction: polyembryony)

1. what is this?

Answer 2

1. fission of the zygote

Question 3

understand this

Answer 3

and this…

Question 4

(Success)

1. for species?
2. for individual?

Answer 4

1. survival, copmete, expand
2. survival, compete, biological immortality

Question 5

(Vegetative Reproduction)

1. used by what?
2. what are three types?

Answer 5

1. bacteria, many plants, and some invertebrate animals
2. budding (yeasts), fission (bacteria), fragmentation (starfish)

Question 6

(Parthogenesis)

1. is what?

Answer 6

1. reproduction with eggs, but no sex (eggs never fertilized)

Question 7

(Vegetative reproduction and parthenogenesis)

1. every member can give birth
2. no members consuming resources without reproducing
3. advantageous in short term (for insects)… but isn’t for long term
4. what is the only group where parthogenesis has not been successful?

Answer 7

4. mammals

(In mammals the genome is parentally imprinted during oogenesis and spermatogenesis, both maternal and paternal chromosome sets are needed for normal development of the offspring.)

Question 8

(Vast majority of animals use sexual reproduction)

(it is somewhat inefficient)

1-4. what are four ways?

Answer 8

1. only half of pop can give birth (two fold cost of sex)
2. males required for fertilization but consume resources year round… decreases number of females that can be supported
3. next generation contains half of parents genes (not complete immortality)
4. courtship and mating costs

Question 9

(So Why Use Sexual Reproduction?)

(Two theories… explain them)

1. Muller’s Ratchet
2. The Red Queen

Answer 9

1. deleterious mutations accumulate in budders - “mutational meltdown of the clones”
2. Our competitors (parasites and such) change very quickly and can then attack… we need to be genetically variable to resist them (coevolutionary pressure)

Question 10

(Why not 3 or 4 sex systems?)

1. seen in what?
2. why aren’t these more common?

Answer 10

1. seen in some higher fungi and lower eukaryotes
2. thought to be unstable and revert to 2 or 1 sex systems

Question 11

(Defining how sex is determined)

1. much of the work has been done in humans… psychologgically imporantat

Question 12

(Types of LEvels or Sex)

1. Genetic
2. gonadal
3. germ cell
4. hormonal
5. phenotypic
6. somatic/(brain

6-7 what are the last two?

Answer 12

1. sex specific chormosomal pattern
2. ovary vs. testis
3. egg vs sperm
4. estrogen vs. testosterone
5. internal and external genitalia, secondary sex characteristics
6. behavioral
7. legal

Question 13

(Mammalian sex determination has been regarded as a 3 step process)

1. genetic (chromosomal) sex is determined when?
2. When does sex determination occur?
3. Sexual differentation of male and female phenotype result from what?

Answer 13

1. at time of fertilization (X containing oocyte fertilized by either and X or Y bearing sperm)
2. when the bipotential or indeifferent gonad is put on the male or female pathway (Y or absence is responsible)
3. spcific secretions of the now determined testis or ovary

Question 14

(Genetic Sex)

1. mammals utilize the dominant Y, single pair method of chromosomal sex determination
2. Has been argued that development of viviparity and a placenta meant that mammals could no longer use the environmental cues or estrogens used by lower animals for sex determination…insteadInstead they had to co-opt/modify other genes to be the pathway trigger, though they could still

preserve the function of those genes that were further down the cascade

Question 15

(Genetic Sex)

1. females are what?
2. all female gametes (oocytes) have what?
3. males are what?
4. sperm contain?

Answer 15

1. XX (homologous)
2. an X (homogametic)
3. XY (heterologous)
4. either an X or Y (heterogametic)

(so sex is set at fertilization)

Question 16

1. what will XO, XX, XXX be?
2. XXXXY?
3. The testis determing factor is the product of what gene?
4. SRY =
5. Sry =
6. SRY =

Answer 16

1. female
2. male (only need the Y)
3. sex-determining region y chromosome
4. human gene
5. gene in other species
6. encoded protein

Question 17

• (SRY/Sry)*
  1. single copy gene with encodes a protein (SRY)
  2. The SRY protein is transported to the nucleus where it binds to DNA to do what?
  3. expressed where prior to gonadal differentiation?
  4. is expression dependent on the presence of primordial germ cells?
  5. XX mice made transgenic only for Sry became male… what does this mean?

Answer 17

2. induce a bend… juxtapose TF at distant sites… which then activate or repress target genes
3. urogenital ridge
4. no
5. sex determination cascade must be autosomal or X-linked

Question 18

(Other functions of the Y chromosome)

1-3. three things… name them

Answer 18

1. spermatogenesis (transgenic XX mice were sterile)
2. regulates (increases) height
3. cardiac traits…. blood pressure and cholesterol metabolism

(much of the remainder called “genetic junk”)