chromosome variation and sex determination Flashcards Preview

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Flashcards in chromosome variation and sex determination Deck (55):
1

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

euploid

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euploid

organisms with multiples of the basic chromosome set

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what can vary among closely related species

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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aneuploidy

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

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

aneuploidy

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

non-disjunction

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non-disjunction

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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when does non-disjunction occur

meiosis

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what increases the chance on on disjunction eveents

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

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trisomy

-3 long chromosomes

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monsomy

-1 long chromosome

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karyotype

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

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euploid detail

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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polyploids

have nice than two chromosome sets

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types of polyploids

triploid, tetraploid, pentaploid and so forth

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one setoff chromosomes

monoploid

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aneuploidy detail

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

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the aneuploid 2n+1 is

trisomic (three bodies)

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the aneuploid with 2n- 1 is

monosomic

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the aneuploid 2n-2 is

nullisomic

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0

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

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does polyploidy and aneuploidy always result in abnormal development

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

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polyploidy is very common in

plants

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where does polyploidy occur in animals

australian frogs

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mammals sex determination

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

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the presence of Y in mammals determines

maleness

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heterogametic

XY

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homogametic

XX

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in some systems males are

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

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

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

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how can inactivated X be seen

as highly condensed 'barr' body

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inactivation of the X chromosome is...

random -maternal or paternal X is inactivated

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inactivation is random and the

maternal or paternal X is inactivated

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which X is inactivated, the male or female

it is random and can occur on either

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the female body is a

mosaic for genes on the x chromosome

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mosaicism

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.

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the Y chromosome

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

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SRY

maleness- determine gene

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The x chromosome

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

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hemizygous

effectively dominant as a single copy

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X chromosome dosage and phenotype

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example of genetic diseases caused by changes in chromosome number

-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

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turner syndrom

-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

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down 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

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klinefeter syndrome

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

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why does having an extra chromosome affect he phenotype so drastically

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

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

..

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what explains why aneuploidys are so much more abnormal than polyploids

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

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X linked recessive traits can be deduced from certain clues

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

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for females to express x linked traits

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

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SRY

sex-determining region Y

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autosomes

any chromosome which is not a sex chromosome

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trisomy 21

down syndrom

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XO example

turner syndrome

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XXY example

klinefeter syndrome