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Genetics > chromosome variation and sex determination > Flashcards

chromosome variation and sex determination Flashcards

1
Q

organisms with multiples of the basic chromosome set are referred to as

A

euploid

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2
Q

euploid

A

organisms with multiples of the basic chromosome set

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3
Q

what can vary among closely related species

A

chromosome number- even if the gene number is the same e.g. chin ease muntjac and indian muntjac have a different number of chromosomes, but about the same number of genes

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4
Q

aneuploidy

A

individuals whose chromosome number differs by one or a small number of chromosomes

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5
Q

individuals whose chromosome number differs by one or a small number of chromosomes

A

aneuploidy

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6
Q

how do cells end up with too many or too few chromosomes

A

non-disjunction

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7
Q

non-disjunction

A

the reason cells end up with too many or too few chromosomes - occurs during meiosis -when chromosomes do not pair with each other properly, meaning one cell will have 1 too many chromosomes and the other 1 too few

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8
Q

when does non-disjunction occur

A

meiosis

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9
Q

what increases the chance on on disjunction eveents

A

as women materials age increases e.g. having a child with down syndrome.. trisomy

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10
Q

trisomy

A

-3 long chromosomes

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11
Q

monsomy

A

-1 long chromosome

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12
Q

karyotype

A

a test to identify and evaluate the size, shape and number of chromosomes in a sample of body cells

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13
Q

euploid detail

A

typical eukaryotes are haploid or diploid, with one or two complete sets of chromosomes. -Organisms with more or few than the normalnumer are aberrant euploid

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14
Q

polyploids

A

have nice than two chromosome sets

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15
Q

types of polyploids

A

triploid, tetraploid, pentaploid and so forth

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16
Q

one setoff chromosomes

A

monoploid

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17
Q

aneuploidy detail

A

an aneuploidy can have a chromosome bnymber either greater or smalltimer than the wild type

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18
Q

the aneuploid 2n+1 is

A

trisomic (three bodies)

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19
Q

the aneuploid with 2n- 1 is

A

monosomic

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20
Q

the aneuploid 2n-2 is

A

nullisomic

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21
Q

0

A

absent e.g. xxy, xyy, xxx, xo

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22
Q

does polyploidy and aneuploidy always result in abnormal development

A

no e.g. mal bees, wasps and ants are monoploid–> developing from unfertilised eggs

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23
Q

polyploidy is very common in

A

plants

24
Q

where does polyploidy occur in animals

A

australian frogs

25
Q

mammals sex determination

A

mammals have an XY sex determination system -males are XY (heterogametic) -females are XX (homogametic)

26
Q

the presence of Y in mammals determines

A

maleness

27
Q

heterogametic

A

XY

28
Q

homogametic

A

XX

29
Q

in some systems males are

A

homogametic e.g. ZW system in butterflies and birds -male- ZZ -female-ZW

30
Q

what happens to one of a mammals X chromosomes early in development

A

it is epigenetically inactivated early in development e.g. either by histone modification or methylation

31
Q

how can inactivated X be seen

A

as highly condensed ‘barr’ body

32
Q

inactivation of the X chromosome is…

A

random -maternal or paternal X is inactivated

33
Q

inactivation is random and the

A

maternal or paternal X is inactivated

34
Q

which X is inactivated, the male or female

A

it is random and can occur on either

35
Q

the female body is a

A

mosaic for genes on the x chromosome

36
Q

mosaicism

A

A female is a mosaic because she consists of a mixture of two kinds of cells: each with different functional chromosomes. Because XY males have a single X chromosome, while XX females have two of them, some kind of adjustment is needed: the X chromosome inactivation. Because of this X inactivation, all women are natural mosaics: although all their cells have the same two chromosomes, one from each parent, the mother’s copy works in some cells, while the father’s works in the others.

37
Q

the Y chromosome

A

most repeated sequence -very few genes -SRY maleness -determining gene -inhertance rathe rot son

38
Q

SRY

A

maleness- determine gene

39
Q

The x chromosome

A

-many genes unrelated to sex determination or sex function -males are hemizygous for X linked genes (effectively dominant as a single copy)

40
Q

hemizygous

A

effectively dominant as a single copy

41
Q

X chromosome dosage and phenotype

A
42
Q

example of genetic diseases caused by changes in chromosome number

A

-monosomies for autosomes in humans die un utero, but monosomy for X ( in 75% to 80% of cases i is caused by a missing x chromosome in the father sperm) causes turn syndrome -many trisomies are lethal, however there are a number of examples of viable trisomies, including trisomy 21 ( in 90% of cases it is caused by non-disjunction in mothers egg), which causes down syndrome

43
Q

turner syndrom

A

-monosomies for autosomes in humans die un utero, but monosomy for X ( in 75% to 80% of cases is caused by a missing x chromosome in the father sperm) causes turn syndrome -klinefeter syndrome

44
Q

down syndrome

A

-many trisomies are lethal, however there are a number of examples of viable trisomies, including trisomy 21 ( in 90% of cases it is caused by non-disjunction in mothers egg), which causes down syndrome

45
Q

klinefeter syndrome

A

results from an xxy karyotype- extra chromosome comes from the mother or the father in this case

46
Q

why does having an extra chromosome affect he phenotype so drastically

A

1) gene balance- genes have evolved to function in a diploid genetic background and disruption that background disrupts their function -explains why aneuploidy are so much more abnormal than polyploids 2) expression of deleterious allele on monosomic autosomes -exaplins why monosomic are typically more severe than corresponding trisomic

47
Q

diagram of how cells end up having too many or too few chromosomes- non-disjunction

A

..

48
Q

what explains why aneuploidys are so much more abnormal than polyploids

A

gene balance- genes have evolved to function in a diploid genetic background and disruption that background disrupts their function

49
Q

X linked recessive traits can be deduced from certain clues

A
  1. more males than females express the trait
  2. the characteristic often skips generations
  3. if the female expresses the characteristic, all of her male offspring will express the trait
50
Q

for females to express x linked traits

A

the male parent must express it and the female must either express it or be a carrier

51
Q

SRY

A

sex-determining region Y

52
Q

autosomes

A

any chromosome which is not a sex chromosome

53
Q

trisomy 21

A

down syndrom

54
Q

XO example

A

turner syndrome

55
Q

XXY example

A

klinefeter syndrome

Genetics (24 decks)

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