Chromosome Variations & Sex Determination Flashcards

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1
Q

Give the definition of euploid.

A

organisms with multiples of the basic chromosome set.

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2
Q

Give the definition of monoploid.

A

an individual of a typically diploid species that has only one set of chromosomes.

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3
Q

Give the definition of aneuploid.

A

Individuals whose chromosome number differs by one or a small number of chromosomes (can have a chromosome number greater/smaller than that of the wild type).

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4
Q

How do cells end up with too many/few chromosomes?

A
  • non-disjunction during meiosis or mitosis
  • daughter cell has 1 too many chromosomes and the other is lacking
  • risk of non-disjunction increases as mother age gets older
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5
Q

Why do extra chromosomes affect the phenotype so drastically?

A
  • gene balance, evolved in diploid organisms and disrupting that background disrupts their function (explains why aneuploids are so much more abnormal than polyploids)
  • expression of deleterious alleles on monosomic autosomes
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6
Q

Give possible changes in chromosome structure.

A

duplication (extra pieces), play an important role in the evolution of the genome
-deletion (missing pieces), can be small eg one gene, or large enough to be visualised on a karyotype
-copy number variations
-inversions and translocations
Inversions are balanced rearrangements, but can lead to duplications or deletions
Translocation is a rearrangement involving a part of one chromosome that has broken off and reattached to a different chromosome

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7
Q

Give the key features of the Y chromosome.

A
  • mostly repeated sequence
  • few genes
  • SRY is key maleness-determining gene
  • inheritance father to son
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8
Q

Give the key features of the X chromosome

A
  • many genes all unrelated to sex-determination or sex function
  • males are hemizygous for X chromosome
  • X-linked traits in humans eg red-green colour deficiency, haemophilia, Duchenne muscular dystrophy
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9
Q

Why does aneuploidy in chromosome 21 have no effect?

A

In female mammals one X chromosome is epigenetically inactivated early in development (lyonisation).

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10
Q

How can X linked recessive traits can be deduced from certain clues?

A
  • more males than females express the trait
  • trait often skips a generation
  • if a female expresses the trait, all of her male offspring will express the trait
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