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CELS191 Molecular Biology, Chromosomes, Genes > Inheritance and genetics > Flashcards

Inheritance and genetics Flashcards

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1
Q

what is a karyotype

A

ordered, visual representation of chromosomes in a cell

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2
Q

how is a karyotype laid out

A

from largest to smallest autosome, followed by sex chromosomes

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3
Q

what is nondisjunction

A

can occur at the first division during anaphase I, where the homologous chromosomes are not split apart, or at anaphase II, where the sister chromatids do not get split apart

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4
Q

effects of nondisjunction

A

Results in aneuploidy - abnormal number of chromosomes in a cell

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5
Q

what is aneuploidy

A

abnormal number of chromosomes in a cell

  • loss or gain of one or a few chromosomes relative to the diploid
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6
Q

examples of aneuploidy

A
  1. Down syndrome- individuals have 3 sets of chromosome 21
  2. Klinefelter syndrome- An individual has two X chromosomes as well as a Y (coded as XXY)
  3. Turner syndrome- an individual with one X chromosome and no other chromosome (sex chromosomes coded as XO)
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7
Q

common methods of prenatal diagnosis of aneuploidy

A
  1. Amniocentesis - at 16-20 weeks a sample of the amniotic fluid taken and the cells centrifuged then analysed which will show how many copies of chromosome 21; 0.1% risk of miscarriage
  2. Chorionic Villus Sampling - 10-13 weeks a blood test measures protein levels using a screen; detects 90% of downs; 1% risk of miscarriage
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8
Q

signs of Downs syndrome

A
  • growth failure
  • mental retardation
  • broad flat face
  • short and broad hands
  • congenital heart disease
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9
Q

signs of Klinefelter syndrome

A
  • tall stature
  • slightly feminised physique
  • poor beard growth
  • breast development
  • testicular atrophy (wastage)
  • mildly impaired IQ
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10
Q

signs of turner syndrome

A
  • short stature
  • widely spaced nipple
  • poor breast development
  • no menstruation
  • rudimentary ovaries
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11
Q

what is a Barr body

A

condensed, inactive X chromosome which females don’t need

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12
Q

implications of Barr body (inactivated X chromosome)

A
  • imaginary cellular mosaic in women, where cells could either have mother’s or father’s X chromosome active
  • can result in certain cells of body being affected by disorders e.g. patches with no sweat glands
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13
Q

examples of chromosome rearrangement in humans

A
  • Lejeune syndrome
  • Williams-Beuren syndrome
  • Philadelphia translocation
  • Duchenne muscular dystrophy
  • Familial down syndrome
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14
Q

what is polyploidy

A

possession of multiple entire sets of chromosomes

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15
Q

cause of familial Down syndrome and how does it behave at meiosis

A

arises from Robertson translocation from gene 14 to gene 21

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16
Q

causes of chromosomal aberrations (loss, gain or rearrangements of parts of chromosomes)

A
  1. deletion
  2. duplication
  3. inversion - segment is reversed
  4. translocation - segment moved from one chromosome to another
    • can be reciprocal, in which non-homologous chromosomes exchanged segments
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17
Q
A
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18
Q

Duchenne muscular dystrophy

A

occurs when a piece of normally inactive X chromosome containing the allele for muscular dystrophy is translocated to the gene 21

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19
Q

Lejeune syndrome

A

children do not learn to speak caused by deletion of tip of chromosome 5

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20
Q

Williams-Beuren syndrome

A

caused by deletion chromosome 7 and results in lowered genetic product, reduced spatial/cognitive awareness, autism, ease with strangers

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21
Q
A
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22
Q

Philadelphia translocation

A

affects 95% of patients with chronic myeloid leukaemia due to TK (a gene product) overexpression- treatable with Gleevec in 90% of cases

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23
Q

Dihybrid cross

A

two genes involved, 9:3:3:1 ratio

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24
Q

test cross

A

used to determine genotype of unknown dominant phenotype

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25
Q

Mendel’s laws

A
  1. Law of segregation: Genes segregate at meiosis so that each gamete contains only one of the two possessed by the parent
  2. Law of independent assortment: alleles of different genes assort independently during gamete formation
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26
Q
A
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27
Q

monohybrid cross

A

one gene involved, 2:1:1 ratio

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28
Q

Lethal Alleles

A

Lethal alleles are those, that when present in a homozygous individual, cause death

29
Q

Polymorphic

A

more than one form; there can be thousands of different alleles in a population but individuals can only have two

30
Q

Incomplete dominance

A

Heterozygotes appear as though the parent genetics have blended; the heterozygote offspring can give rise to homozygous “non-blended” offspring

31
Q

Co-dominance

A
  • when both phenotypes exists side by side within the organism
  • e.g. ABO blood antigen system
32
Q

Epistasis

A

one gene effects the action of another - gene 2 cannot function unless gene 1 is expressed

33
Q

Polygenic traits

A

phenotype controlled by many genes that have an additive effect; character appears continuous or quantitative

  • e.g, skin colour, weight, milk yield, IQ, height
  • has a normal distribution, more individuals are around the average value
34
Q

what determines phenotype

A

genotype and environment

35
Q

Pleiotropy

A

one gene has many effects e.g. sickle cell gene produces many symptoms; colouration pattern and cross eyes of Siamese cats and produced by the same gene

36
Q

polymorphism

A

one gene for a particular trait has many different alleles. however an individual can only has two alleles, one from each parent

37
Q

linked gene and features

A
  • genes found on same chromosome so do not assort independently
  • Off spring are not in normal test cross 1:1:1:1 ratio; instead two heavily favoured genotypes and 2 minority recombinant genotypes
  • if less than 50% of offspring show recombinant phenotype (more than 50% show parental phenotype), we can assume genes are linked
38
Q

features of

A
39
Q

autosome

A

chromosome that does not determine sex

40
Q

sex chromosome

A

chromosome that determines sex of individual

41
Q

inheritance pattern of X linked recessive gene

A
  • males more likely to show trait than females because they don’t have a backup X chromosome
  • father with the trait will transmit the mutant allele to all daughters but to no sons
  • carrier woman who mates with a normal male will pass the mutation to half her sons and half her daughters
  • carrier woman mates with a male with the trait, there is a 50% chance that each child will have the trait
  • e.g. haemophilia
42
Q

crossing over

A
  • Occurs during meiosis I
  • Two chromatids of a tetrad (one from each pair) cross over at random points and swap genetic material
  • causes recombinant phenotypes
  • the proportion of recombination gametes is called combination frequency
43
Q

recombinant chromosome

A

chromosome in an offspring that has a genotype not found in either parent, due to crossing overcrossing over in meiosis.

44
Q

how is recombination frequency used for gene mapping

A
  • The smaller the distance between two genes- the less likely chiasma will be formed between them
  • Distant (unlinked) genes have a recombination frequency of 50% (half recombinant and half parental types)
  • Close genes have recombination frequencies of between 0-50%
  • There is a near linear relationship between distance and recombination frequency
45
Q

population

A

ocalised group of individuals of the same species

46
Q

gene pool

A

total aggregates of genes (and their alleles) in the population at one time

47
Q

hardy-weinberg theory

A

allele frequencies remain constant over time unless acted upon by evolutionary forces

48
Q

assumptions of hardy-weinberg theory

A
  • No migration
  • No mutation
  • No natural selection
  • random mating
  • large population size
49
Q

hardy-weinberg equation

A
  • allele frequency: p + q = 1
  • genotypic frequency: p2 + 2pq + q2 = 1
50
Q

how fast does random genetic drift occur in small populations

A

rapidly

51
Q

what causes changes in allele frequency

A
52
Q

what does telocentric mean

A

when centromere is at extreme end of the chromosome

53
Q

what does acrocentric mean

A

when centromere is at the near end of the chromosome

54
Q

what is an autotriploid

A

three of the same chromosomes

55
Q

what is an autotetraploid

A

four of the same chromosomes

56
Q

what is an allotetraploid

A

four sets of chromosomes

57
Q

what is an allohexaploid

A

six sets of chromosomes

58
Q

natural selection

A

individual has a favourable trait which gives it an advantage in its environment so is more likely to reproduce and pass on its favourable allele

59
Q

genetic drift

A

random change in allele frequency in a small population over generations due to sampling errors

60
Q

bottleneck effect

A
  1. sudden environmental change which causes a drastic reduction in population size
  2. causes different allele frequency which is not representative of original population
  3. undergo genetic drift due to small population
61
Q

founder effect

A
  1. small population from original group gets separated/isolated
  2. different allele frequency not representative of original population
  3. genetic drift acts
62
Q

cline

A
  • gradual change in phenotypes across geographic areas
  • slightly different environment causes slightly different phenotypes
  • slightly different allele frequency
  • still same species as long as they can interbreed
63
Q

migration

A

individual from one population moves to another population

  • introduce new alleles, changes allele frequency
  • changes population size
64
Q

mutation

A
  • only source of new alleles in gene pool
  • normally harmful
  • acted upon by natural selection
65
Q

stabilising selection

A

reduces variation but does NOT change the mean

66
Q

directional selection

A

changes the mean value towards one extreme

67
Q
A
68
Q

disruptive selection

A

favours the two extremes producing two peaks

69
Q

selection selection

A

individuals mate with individuals of opposite sex with certain traits they find attractive, selecting for those certain traits

CELS191 Molecular Biology, Chromosomes, Genes (2 decks)

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