chromosome behaviour during cell divisions Flashcards

1
Q

what occurs in each of the following sections of prophase I: leptotene, zygotene, pachytene, diplotene

A

leptotene: chromosomes start to condense
zygotene: homologous chromosomes become closely associated to form pairs of chromosomes consisting of 4 tetrads
pachytene: crossing over between pairs of homologous chromosomes to form chiasmata
diplotene: homologous chromosomes continue to separate but remain attached by chiasmata

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2
Q

what is meant by the term ‘cross’?

A

the fusion of male gametes from one individual and female gametes from another

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3
Q

define ‘monohybrid cross’

A

crosses between true breeding strains with alternative forms of a single trait

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4
Q

what information does a reciprocal cross give you?

A

whether inheritance of a trait depends on sex

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5
Q

what is Mendel’s principle of segregation?

A

alleles separate from eachother during the formation of gametes in meiosis

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6
Q

what is meant by product rule?

A

the probability of two interdependent events occurring simultaneously, the product of each of their individual probabilites

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7
Q

what is meant by sum rule?

A

the probability of occurance of any mutually exclusive events is the sum of the probability of individual events

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8
Q

what is the Chi-squared test used for?

A

to determine whether a difference is due to chance, and if the null hypothesis should be rejected

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9
Q

what is meant by complementation?

A

when 2 strains of an organism with different homozygous recessive alleles produce offspring with wild-type phenotype when crossed

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10
Q

why does linkage happen?

A

alleles on the same chromosome will not assort independently and will co-segregate at meiosis

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11
Q

what indicates linkage?

A

greater observed number of parental phenotypes than recombinants or by RF <50%

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12
Q

how is RF calculated?

A

total recombinants/total progeny x100

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13
Q

what causes RF to reach 50%?

A

one or more chiasmata between 2 genes in every meiosis

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14
Q

what does a dominance test test?

A

studies the phenotype of the heterozygote F1; the functional relationship of alleles on the same gene

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15
Q

what does a complementation test study?

A

the phenotype of F1, tests the functional relationship of two recessive mutations

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16
Q

what are the characteristics of an autosomal recessive disease?

A
  • heterozygotes unaffected
  • 2 heterozygotes have 25% chance of having affected offspring
  • 2 homozygous individuals will have affected offspring only
    e. g: cystic fibrosis
17
Q

what are the properties of an autosomal dominant disease?

A
  • every affected individual has 50% chance of having affected offspring
  • disease cannot skip generations
  • e.g. Huntington’s disease
18
Q

what are the properties of an X-linked recessive disease?

A
  • hemizygous males and homozygous females affected
  • female carriers have 50% chance of having affected sons
  • affected males cannot give traits to sons
  • e.g. Haemophilia A
19
Q

what are the properties of an X-linked dominant disease?

A
  • hemizygous males and heterozygous females affected
  • affected male cannot give trait to sons but gives it to his daughters
  • focal dermal hypoplasia