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GED > Sex-determination and Sex-linked inheritance > Flashcards

Sex-determination and Sex-linked inheritance Flashcards

1
Q

what are the two types of sex determination in animals

A

genetic and environmental

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2
Q

what is sex determination determined by in some animals such as alligators and turtles

A

temperature- the temperature at which eggs develop determines the sex of the animal in question

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3
Q

how many times greater is the x chromosome compared to the y chromosome

A

2.5 times

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4
Q

autosomes

A

non-sex chromosomes

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5
Q

on x chromosomes how many genes are in the x specific region

A

over 1000 genes

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6
Q

how many genes are found in the male specific region of the y chromosome

A

80

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7
Q

pseudo autosomal region

A

found at the tips of both the x and y chromosomes which is shared between the two
roughly 20 genes
region of homology

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8
Q

what is the PAR region crucial for

A

region of homology and is required for x-y pairing in meiosis

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9
Q

homogametic sex

A

females

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10
Q

heterogametic sex

A

males

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11
Q

where did evidence that that the Y chromosome confers the male sex chromosome

A

aneuploidy observations

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12
Q

XO individuals

A

females

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13
Q

XXY individuals

A

males

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14
Q

aneuploidy

A

an abnormal number of chromosomes

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15
Q

what syndrome does X0 lead to

A

Turner syndrome

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16
Q

what does Y counteract in males

A

two Xs

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17
Q

is all of the y chromosome required to be defined as a male

A

no

18
Q

how many genes are required to be defined as a male

A

one

19
Q

what is the key gene that indicates whether an individual will be male

A

SRY( sex-determining region on the Y)

20
Q

what evidence is there that concludes the SRY is necessary for maleness

A
  1. Individuals with two X chromosomes but with an added translocation coming from the Y chromosome and containing SRY presented as males. This is very rare and is called sex reversal
  2. individuals with mutations in the SRY gene. These individuals had heterogametic sex however were female
  3. expressing SRY using a transgene was enough to confer the male sex to mice that would’ve been otherwise female
21
Q

what is SRY

A

transcription factor that recognises specific DNA sequences found in promotor of genes

22
Q

what does the binding of SRY at promoters activate

A

gene expression

23
Q

outline gonad development

A
  1. development starts in the genital ridge (entirely made of somatic cells ) in week 4
  2. at week 5 and 6 the future germ cells start migrating from another area of the embryo and settle in the embryo ridge
  3. when complete, the region is defined as the indifferent gonad and contains both germ cells and somatic cells
  4. at week 7, SRY is activated and expressed and its activity as a TF enables the gonad to become the ovaries
24
Q

do all species have an SRY

A

no

25
Q

what system is used for sex determination in birds

A

ZW system

26
Q

in birds, what chromosomes make males

A

ZZ (homogametic)

27
Q

in birds, what chromosomes make females

A

ZW (heterogametic)

28
Q

gynandromorph

A

a sex mosaic

29
Q

in chickens that are classified as gyandromorph, how is sex decided

A

each cell defines its own sex as sex is decided in an autonomous manner and according to their sex chromosomes

30
Q

cell-autonomous sex identity (CASI)

A

every cell decides whether to express male or female characteristics

31
Q

what are the 5 ways that sex chromosomes could have evolved

A
  1. evolved from autosomes
  2. Y chromosome in mammals acquired a sex-determining locus (SRY for humans) which gave rise to proto-X and Y chromosomes
  3. Y accumulates specific genes providing advantages to males producing a chromosomal region that lacks homology with the X chromosome. Thus, due to a lack of sequence homology, there is no recombination between these sex-specific regions of the chromosomes.
  4. since pairing is essential in meiosis, PAR appears and makes meiosis possible
  5. parts of the Y chromosome that don’t provide useful function are lost through deletions and mutations making the Y chromosome much smaller
32
Q

what led to the discovery that sex chromosomes can pass on their genes in a way that didn’t fit Mendelian phenotypic ratios

A

Thomas Hunt Morgan’s work on a spontaneous mutant fly with white eyes

33
Q

Morgan’s crosses with the white mutant gave sex-biased phenotypic ratios: Cross 1- White male and Red female

A

All F1 were red eyes and concluded that red is dominant and white, w, is recessive

34
Q

Morgan’s crosses with the white mutant gave sex-biased phenotypic ratios: Cross 2- F1 female was crossed with an F1 male

A

progeny were a 3:1 red-white ratio AND all white-eyed flies are male. In addition, red-eyed flies show a 2:1 ratio of females to males

35
Q

Morgan’s crosses with the white mutant gave sex-biased phenotypic ratios: Cross 3- a white male and an F1 female (heterozygote for small w)

A

This cross produced 1 red male, 1 red female 1 white male and 1 white female. So, this way he showed that white-eyed female are possible

36
Q

Morgan’s crosses with the white mutant gave sex-biased phenotypic ratios: Cross 4-white female and mate it with an F1 male

A

This produced red-eyed females and white-eyed males. In that scheme he got a perfect co-segregation of sex and eye colour.

37
Q

what was Morgan’s research parallel to

A

with cytological observations on the chromosomes of Drosophila

38
Q

cytological observations on the chromosomes of Drosophila

A

Drosophila has 4 pairs of chromosomes, 3 pairs are for autosomes (homomorphic), but 1 pair is for sex chromosomes (male pair is heteromorphic):

39
Q

from his research, what could Morgan hypothesis

A

that not all chromosomes are equivalent and to place the white mutation on X

40
Q
A

GED (3 decks)

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