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BIO 202 > Sex Determination + Sex Linked Inheritance > Flashcards

Sex Determination + Sex Linked Inheritance Flashcards

1
Q

Hermaphrodite

A

Organisms with BOTH female and male gametes

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2
Q

Sex determination in most mammals and humans

A

Female = XX
Male = XY

Y is the determining sex chromosome

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3
Q

The y chromosome is the…

A

sex determining chromosome

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4
Q

Other Binary Sex Determination Systems: (3.5)

A

1) X-O System
2) Z-W System
3) Haplo-Diploid System

3.5) Environmental Factor Dependence

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5
Q

X-O System

A

Determine by number of X chromosomes:

Male = X
Female = XX

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6
Q

Z-W System

A

Opposite of our system:

Male = ZZ
Female = ZW

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7
Q

Haplo-Diploid System

A

Sex determined by ploidy:

Male = Haploid –> Develops from unfertilized egg
Female = Diploid –> Develops from fertilized egg

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8
Q

Environmental Dependent Sex Determination

A

Some animals depend on environmental conditions to determine sex

–> Ex: Like some turtles depend on temperature to determine sex

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9
Q

In humans, what is the chance of an offspring being female or male?

A

50%

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10
Q

SRY Gene

A

A gene found ONLY on the Y chromosome (NOT found on the X chromosome)

= “Sex determining region of the Y chromosome”

Responsible for turning a mammalian embryo to a male

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11
Q

SRY Gene encodes for

A

a protein (transcription factor) that triggers/regulates the expression of many other genes that leads to a cascade of male development

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12
Q

Individuals w/ SRY gene vs w/o

A

With SRY Gene = Testes develop

Without SRY Gene = Ovaries develop

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13
Q

“femaleness” is the…

A

default pathway

–> SRY is needed to trigger a cascade, but without it, the cell would undergo the female development

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14
Q

When SRY gene was injected into a female zygote, what happened?

A

The mouse that developed had male reproductive organs

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15
Q

What did the experiment with the SRY transgenic mouse demonstrate?

A

SRY gene was not only necessary but also SUFFICIENT to change the path of development from female to male

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16
Q

X Chromosome

A

Contains ~1,000 genes –> Many of which are ESSENTIAL to life

17
Q

What type of abnormality in sex chromosomes is inviable?

A

No X chromosome

18
Q

Y chromosome

A

Gene poor: contains ~78 genes

–> None are essential to life

–> Paternally inherited

19
Q

Why does the Y chromosome stay constant through generations?

A

Because X + Y are not homologs so the Y chromosome escape recombination

== Unless mutations occur, a father will pass down almost an exact copy of his own Y chromosome to his son

20
Q

X and Y are NOT _____________ but they behave like __________ for _____________

A

1) Homologs
2) Homologs
3) Meiosis I

21
Q

Why are X and Y not homologs?

A

They are quite difference in sequence and the genes they carry

22
Q

How do X and Y “act” like homologs in meiosis?

A

Through the pseudo-autosomal regions

23
Q

Pseudo-Autosomal Regions

A

Small sections at the ends of the X and Y chromosomes that have homologous sequences

–> Allows for “homologous” pairing during meiosis but NOT crossing over

24
Q

How does a female having 2 X chromosomes affect gene dosage compared to males (with only 1X)?

A

There is no effect due to inactivation of an X chromosome in females

25
Q

Barr Body

A

Compacted/Condensed X chromosome = inactive

26
Q

X Inactivation

A

During female development, one X chromosome per cell condenses into a compact + INACTIVE barr body

27
Q

The selection of which X chromosome to inactivate is…

A

random

28
Q

Mosaic of X Chromosomes

A

The X that is inactivated in each cell is not consistent: some cells may express the maternal X and others may express the paternal X

–> ~50% of cells will have the maternal X activated and the other 50% will have the paternal X activated

29
Q

Calico Cats

A

Get their patchy coloration due to different patches of cells with different active X chromosomes that encode for different hair color trait

30
Q

Sex-Linked Gene

A

A gene located on either sex chromosome (don’t solely determine sex)

31
Q

Fathers vs Mothers X Allele Passage

A

Fathers –> Pass their X allele only to daughters

Mothers –> Pass an X allele to sons and daughters

32
Q

To get a homozygous recessive daughter in an X linked trait you must cross…

A

A heterozygous female (carrier) with an affected male (hemizygous recessive)

33
Q

Aneuploidies of sex chromosomes are more _____________ than in autosomes

–> Because…(2)

A

Tolerated

Because:
1) Y chromosome carries very few genes, none of which are essential
2) Extra X chromosome gets inactivated as barr bodies

34
Q

More males have _________________ than do females

A

X-Linked Recessive Diseases

35
Q

Trisomy X

A

XXX

–> Female with extra X

36
Q

Klinefelter

A

XXY

–> Male with extra X

37
Q

Turner Syndrome

A

X

–> Female with missing X

BIO 202 (33 decks)

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