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Flashcards in Sex Determination Systems Deck (32)
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1
Q

Single allele at a gene locus determines the sex of that individual.
ex. yeast exist as 2 different haploid sexes: a or alpha.

A

Genic sex determination

2
Q

Combination of sex chromosomes determine the sex of that individual
ex. ZW female and ZZ Male in birds or XX female and XO in insects

A

Genotypic sex determination

3
Q

Presence of Y chromosome dictates Male or Female

A

Y determination mechanism

4
Q

XX females

A

Homogametic

5
Q

XY males

A

Heterogametic

6
Q

Aligns with X chromosome during meiotic synapsis.

A

Pseudoautosomal regions (PARs)

7
Q

Euchromatin has about 50-60 genes involved in sex determination.

A

Male-specific region of the Y (MSY)

8
Q
  • Becomes active at about 6-8 weeks during development.

- Region encodes protein called Testes Determining Factor (TDF) which directly controls testes development

A

Sex-determining Region of Y (SRY)

9
Q

Absence of TDF results in:

A

Development of gonads into ovaries.

10
Q

How was SRY first identified?

A

Observation: sex reversal in humans
Hypothesis: SRY is essential for male sex determination

11
Q

Cytogenic; has deletion in the Y chromosome.

A

XY females

12
Q

Cytogenic; has small pieces of Y chromosome attached to X.

A

XX males

13
Q

SRY first identified, cont…

experiment in mice: SRY gene ortholog cloned and introduced into XX mouse embryos

A

Result: Introduced trans gene caused normal male development from the XX mice.
Conclusion: SRY causes male testes development

14
Q

Evidence for Y chromosome mechanism

A

Turner Syndrome
Klinefelter syndrome
XYY male

15
Q

XO female
Usually embryonic lethal
Secondary sexual characteristics poorly developed
short stature

A

Turner syndrome

16
Q

XXY (male)
Breast development
Above average height

A

Klinefelter syndrome

17
Q

XYY (male)
Taller than average
antisocial?

A

XYY male

18
Q

the inactive X chromosome in a female somatic cell, rendered inactive in a process called lyonization, in those species in which sex is determined by the presence of the Y (including humans) or W chromosome rather than the diploidy of the X or Z.

A

Barr Bodies

19
Q

Silencing of one X chromosome in female allows for the same level of expression for genes on the X chromosome in males and females.

A

Gene dosage compensation

20
Q

total # if X chromosomes - 1 =

A

of Barr bodies in somatic cells

21
Q

Only X chromosome is changed from euchromatin to heterochromatin about 16 days after fertilization
-deactivation occurs randomly between 2 X chromosomes in every cell.

A

Lyonization

22
Q

All mitotic descendents of the cell inherit that inactivation pattern.

A

Epigenetic phenomena

23
Q

Femalse are mosaics

A

Lyonization

ex. calico cat: only some genes are coded for orange and some for black. Determined randomly.

24
Q

Genes on X or Y chromosome

A

Sex linked genes

25
Q

Many linked genes are “innocent passengers”, meaning;

A

they don’t have anything to do with sex determination

26
Q

Sex linked genes in humans:

A

more than 100 traits known, examples:
color perception
blood clotting factors
dystrofen: large protein for muscle cell structure

27
Q

Sex-linked traits in humans:

A
  1. X-linked recessive inheritance

2. X-linked dominant inheritance

28
Q
  • Trait occurs more frequently in males because males are hemizygous for genes on the chromosome.
  • Females express the trait when they are homozygous for the allele. Heterozygotes are carriers.
A

X-linked Recessive Inheritance

29
Q

What proportion of the sons of an affected mother would show the trait?

A

100%

30
Q

What proportion of the sons of a carrier mother would show the trait?

A

50%

31
Q

A homozygous normal mother marries an affected male, what proportion of their daughters would show the trait?

A

0%

32
Q

An affected mother marries a normal male, what proportion of their daughters would show the trait?

A

0%