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MODULE 5 - Reproduction > GENETICS > Flashcards

GENETICS Flashcards

1
Q

What are cytogenetics?

A

The study of inheritance in relation to the structure and function of chromosomes

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2
Q

What do most chromosomal abnormalities lead to?

A

Most chromosomal abnormalities are not compatible with survival leading to spontaneous miscarriages or stillbirths

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3
Q

What is associated with chromosomal abnormalities which are compatible with survival?

A

Infertility, embryonic loss, growth and development abnormalities

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4
Q

What is a karyotype?

A

An individuals full set of chromosomes

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5
Q

How are chromosomes arranged in a karyotype?

A

Chromosomes are arranged in pairs in order of their size

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6
Q

What is the role of autosomes?

A

Autosomes are the chromosomes which determine somatic characteristics

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7
Q

What is the role of allosomes?

A

Allosomes are chromosomes which are involved in sex determination

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8
Q

Describe the process of karyotype preparation

A
  1. Nucleated cells are isolated from the animal
  2. Cells are grown in culture with mitogens to stimulate mitosis
  3. Cells are arrested in metaphase through the disruption of the mitotic spindle
  4. Cells are dropped onto the slide and stained
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9
Q

Why are cells arrested at metaphase when preparing a karyotype?

A

All of the chromosomes are condensed and easier to visualise

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10
Q

Which stain is used for karyotype staining?

A

Giesma stain

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11
Q

What determines the banding pattern seen in chromosomes stained in karyotyping?

A

The banding pattern is determined by the density of the heterochromatin unique to each chromosome

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12
Q

How can karyotyping be used to detect chromosomal abnormalities?

A
  • Changes in the normal banding pattern can be used to detect genetic abnormalities
  • The position of the centromere relative to the ends of the chromosome
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13
Q

Describe the three ways that centromere position can be displayed

A

Metacentric: centromere lies at the centre of the chromosome
Acrocentric: centromere lies just off centre of the chromosome
Telocentric: centromere lies close to the telomeres

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14
Q

What is chromosomal painting?

A

Chromosomal painting is the use of fluorescent probes to identify specific chromosomes

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15
Q

What are the two main chromosomal abnormalities?

A

Numerical abnormalities
Structural abnormalities

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16
Q

What are aneuploidy chromosomal abnormalities?

A

Aneuploidy chromosomal abnormalities are the presence or absence of one or more chromosomes

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17
Q

What are trisomy genetic abnormalities?

A

Trisomy is used to describe an individual who has three copies of a chromosome instead of two

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18
Q

What are monosomy genetic abnormalities?

A

Monosomy is used to describe an individual who has lost one or one pair of chromosomes

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19
Q

What is the ‘gene dosage effect’?

A

The phenotype of an individual is a direct result of the cumulative imbalance of individual genes located at a chromosome region

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20
Q

What is nondysjunction?

A

Nondysjunction is the failure of chromosomes to separate producing daughter cells with chromosomal abnormalities. Nondysjunction can occur in meiosis 1 or meiosis 2

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21
Q

What leads to a mosaic genotype?

A

Genetic mosaicism is the presence of two or more karyotypes derived from a single zygote in an individual

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22
Q

What leads to a chimera genotype?

A

Genetic chimerism is the presence of two or more karyotypes derived from two different zygotes (zygote fusion)

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23
Q

Give an example of chimeras

A

Freemartin cattle

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24
Q

Describe how chimerism occurs in Freemartin cattle

A

One male and one female embryo develop with placental anastomosis allowing blood to be shared between the two foetuses. This causes the female foetus to be exposed to male hormones and become ‘masculinised’ (infertile) and the male foetus to be sub-fertile

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25
Q

What is one of the most common chromosomal disorders seen in horses and how does is alter the mare phenotype?

A

Monsomy X leads mares to be small in size with small ovaries and resulting infertility

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26
Q

What is XY sex reversal syndrome?

A

The genetic sex of the individual is inconsistent with their phenotypic sex, leading to infertility

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27
Q

What is the other name used for monosomy X?

A

Turner’s syndrome

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28
Q

What is the other name used for XXY trisomy?

A

Klinefelters syndrome

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29
Q

What are genetically balanced chromosomal abnormalities?

A

When a chromosome breaks and is not restored to its original conformation but all of the genetic information is retained, just in a different order

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30
Q

What are genetically unbalanced chromosomal abnormalities?

A

When a chromosome breaks and is not restored to its original conformation with some genetic information missing

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31
Q

What is Robertsonian translocation?

A

Robertsonian translocation is when the centromere of two acrocentric chromosomes fuse together to give one large metacentric chromosome, causing a loss in genetic information

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32
Q

What is the most common consequence of Robertsonian translocation?

A

Embryonic loss

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33
Q

What are Mendelian genetics?

A

The study of certain patterns of how traits are passed from parent to offspring

34
Q

What is the most common type of genetically inherited single gene disorder?

A

Autosomal recessive

35
Q

What are the three main classes of single gene mutations?

A

Deletions
Insertions
Point mutations

36
Q

What is the name used to describe a mutation which replaces a codon with a stop codon (premature stop codon)?

A

Nonsense mutation

37
Q

What is the name used to describe a mutation which replaces an amino acids with a different amino acid?

A

Missense mutation

38
Q

What is a somatic mutation?

A

A mutation which arises in somatic cells which is passed on only to the daughter cells

39
Q

What is a germline mutation?

A

A mutation which arises in germ cells (sperm or ova) which is passed to every cell in the body

40
Q

What is the term used to describe when a gene is expressed in the heterozygous state?

A

Dominant

41
Q

What is the term used to describe when a gene is expressed in the homozygous state?

A

Recessive

42
Q

How does the body ensure that females, like males, have one functional copy of the X chromosome in each body cell (except the ova)?

A

X-chromosome inactivation (one X chromosome is inactivated in every female somatic cell)

43
Q

How do tortoiseshell cats express their coat colour?

A

Both the X chromosomes in the female are only partially inactivated and only in local areas, causing the patches of colour

44
Q

How can male cats express a tortoiseshell coat?

A

If the male cat has an XXY trisomy chromosomal abnormality

45
Q

What are Barr bodies?

A

Inactivated X chromosomes seen in female cells

46
Q

Why does X chromosome inactivation not eliminate the XXY trisomy dosage difference?

A

Due to pseudochromosomal regions (regions of the X chromosome containing genes also present on the Y chromosome) which ‘escape’ X chromosome inactivation

47
Q

What is autosomal recessive inheritance?

A

Autosomal recessive inheritance is when an individual inherits two mutant alleles from carrier parents

48
Q

Why are autosomal recessive diseases so common?

A

Both parents are carriers so often breeders don’t realise that these individuals are carrying mutant alleles before breeding them and producing offspring which may express the disease

49
Q

Give four examples of autosomal recessive diseases

A
  • Canine leukocyte adhesion deficiency
  • Von willebrands disease
  • Osteogenesis imperfecta
  • Severe combined immunodeficiency (SCID) in horses
50
Q

What are some of the key factors seen in autosomal recessive inheritance?

A
  • Males and females are affected by the condition at an equal frequency
  • Parents are carriers
  • 25% of offspring are likely to be affected by the disease
  • Affects one generation and not the parents
51
Q

Give an example of an autosomal recessive mutation that is actually positively selected for by some cattle breeders?

A

Double muscling/muscle hypertrophy in cattle

52
Q

What are some of the common complications of Double muscling/muscle hypertrophy in cattle?

A
  • Weak bones
  • Enlarged tongue (macroglossia)
  • Small feet
  • Dystocia
53
Q

What is genetic heterogeneity?

A

Genetic heterogeneity is when a single phenotype can be derived from different genetic mutations

54
Q

Give an example of a disease which expresses genetic heterogeneity

A

Pyruvate kinase deficiency

55
Q

What is autosomal dominant inheritance?

A

Autosomal dominant inheritance is when an individual inherits one mutant allele from one heterozygous parent carrying the mutation

56
Q

Why are autosomal dominant diseases so rare?

A

The parent carrying the mutation is heterozygous so the disease is phenotypically expressed and most breeders won’t breed an individual with a genetic disease

57
Q

What complication can arise that makes autosomal dominance diseases slightly more common?

A

When the disease is late age onset

58
Q

Give two examples of autosomal dominant diseases? Which of these diseases is a late age onset disease?

A
  • Hyperkalaemic periodic paralysis (HYPP) in horses
  • Polycystic kidney disease in cats (late onset disease)
59
Q

What are some of the key features of autosomal dominant diseases?

A
  • Males and females are affected by the disease at an equal frequency
  • 50% of offspring are likely to be affected by the disease
  • Every generation is affected
60
Q

Why is there no male to male offspring transmission in X-linked recessive inheritance?

A

There is no male to male offspring transmission as the male offspring inherits the Y gene from his father and the X gene from his mother

61
Q

What are some of the key features of X-linked recessive inheritance?

A
  • No male to male offspring transmission
  • Affects alternate generations
62
Q

What is incomplete penetrance?

A

Incomplete penetrance is when an individual carries a disease but does not express the disease phenotype

63
Q

What is incomplete dominance?

A

Incomplete dominance is when both alleles are expressed in a heterozygote

64
Q

What is quantitative genetics?

A

The study of the inheritance of quantitative traits and their mechanisms

65
Q

Define quantitative traits

A

Quantitative traits are phenotypes that vary continuously

66
Q

What are the two factors which contribute to quantitative traits?

A

Polygenetics and environmental factors

67
Q

What are polygenetics?

A

Polygenetics is when a trait is influenced by two or more genes

68
Q

What is the phenotypic value of an individual?

A

The phenotypic value of an individual is the combined effect of the genotypic value (G) and the environmental deviation (E): (P=G+E)

69
Q

What is a continuous trait?

A

A phenotype which can be distributed on a continuum

this is the same as a quantitative trait

70
Q

What is a discontinuous trait?

A

A phenotype which is placed in a discrete category

71
Q

What are the three factors which contribute to genetic variability?

A

Additive gene action (VA)
Dominance gene action (VD)
Epistatic gene action (VI)

VG=VA+VD+VI

72
Q

What is additive gene action?

A

Additive gene action is the cumulative effect of alleles at multiple gene loci which contribute to one phenotype

73
Q

What is epistasis gene action?

A

Epistasis gene action is when the expression of one gene is affected by the expression of another gene

74
Q

What is a common example of epistasis gene action?

A

Coat colour in Labradors

75
Q

What are threshold traits?

A

Threshold traits are quantitative traits where there is a clear non-linearity at the phenotypic level, however their inheritance is determined by polygenetics and environmental factors

76
Q

Describe briefly the liability threshold module of threshold traits

A

All of the factors which influence threshold traits, whether polygenetic or environmental are described as liability. Liability can be plotted and only individuals who reach threshold on the liability scale will express the threshold trait

77
Q

What is heritability?

A

Heritability is the portion of phenotypic variation that is due to genotypic variation

78
Q

What is the difference between broad sense heritability and narrow sense heritability?

A
  • Broad sense heritability is the phenotypic variation dependent on the genotypic variation
  • Narrow sense heritability is the action of additive gene action on phenotypic variation
79
Q

Why is understanding the heritability of a trait so important for breeding programmes?

A

Because if a trait has a large genetic contribution then it can be selected for, however if a trait has a low genetic contribution, it is more beneficial to alter the environmental conditions

80
Q

Describe the heritability scale

A

The heritability scale runs from 0 (no genetic factors contributing to that trait) to 1 (trait is completely determined by genetic factors)

81
Q

What are quantitative trait loci (TQIs)?

A

Stretches of DNA which contain or link genes to a quantitative trait

MODULE 5 - Reproduction (22 decks)

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