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LF104: Molecules, Cells And Organisms > Lecture 49. Human Genetics - Pedigree Analysis > Flashcards

Lecture 49. Human Genetics - Pedigree Analysis Flashcards

1
Q

What are the two types of genetic disease variation?

A

Simple Mendelian
Complex or multifactorial

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2
Q

What are simple Mendelian diseases?

A

Tractable/Easy to investigate
Single gene mutation associated with disease
Disease due to a typically rare allele in the population ( 1 in >2000 individuals)
Readily defined pattern of inheritance

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3
Q

What are some examples of simple Mendelian diseases?

A

Huntington’s disease, cystic fibrosis, Duchenne muscular dystrophy, BRCA1 breast cancer

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4
Q

What are complex diseases?

A

Difficult to investigate
Allelic variation in multiple genes associated with disease
Cumulative affect of weakly expressed common alleles
Disease risk is typically influenced by non-genetic factors (environment, life-style and age)

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5
Q

What are examples of complex diseases?

A

Various cancers, heart-related diseases, irritable bowel diseases, diabetes, Parkinsons, Alzheimers

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6
Q

What is pedigree analysis?

A

Use of a diagram to summarise the inheritance of discrete trait (phenotype) in a family history

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7
Q

What shape represents females in a pedigree chart?

A

Circle

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8
Q

What shape represents males in a pedigree chart?

A

Square

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9
Q

What shape represents an unknown sex in a pedigree chart?

A

Diamond

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10
Q

What does a double line in a pedigree chart mean?

A

Mating between relatives

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11
Q

What does a black oval mean in a pedigree chart?

A

Stillbirth or spontaneous abortion

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12
Q

What represents generations in a pedigree chart?

A

Roman numerals

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13
Q

Why do pedigree analysis?

A

Knowledge about simple ‘Mendelian’ traits
Ethical limits: controlled matings are not possible

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14
Q

What are the limitations in a pedigree diagram?

A

Sampling: small family sizes per generation
Inaccurate & incomplete data: e.g false information about parentage or missing clinical records or phenotype data
Demographics: migration & intermating

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15
Q

What are the aims of pedigree analysis?

A

Determine the mode of inheritance (sex-linked/autosomal or dominant/recessive)
Calculate the probability of an affected individual based on recent family history (e.g for genetic counselling)

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16
Q

What is autosomal recessive inheritance?

A

If d denotes a disease allele, then dd denotes genotypes that are affected by the disease, whereas DD and Dd are disease-free
Disease will typically not occur in every generation
Affected individuals can be born to unaffected parents
Males and females equally affected

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17
Q

What are two examples of autosomal recessive diseases?

A

Cystic fibrosis and Tay-Sachs disease

18
Q

What is autosomal dominant inheritance?

A

If D denotes a disease allele, then dd denotes genotypes that are disease free
In most cases DD will be lethal, so all diseased individuals will be heterozygous Dd
Disease will be found in every generation every affected individual has an affected parent
Males and females equally affected

19
Q

What are three examples of autosomal dominant diseases?

A

Huntington’s disease, hereditary retinoblastoma and achondroplasia

20
Q

What are examples of X chromosome sex-linked recessive diseases?

A

Haemophilia, red-green vision deficiency, Christianson syndrome, fragile X syndrome and Duchenne muscular dsytropy

21
Q

What are examples of Y chromosome sex-linked recessive diseases?

A

Y chromosome infertility and Swyer syndrome

22
Q

If a female carrier of an X-linked recessive inheritance disease and a normal male bred, what phenotypes would there offspring be?

A

Half of the males and females would be normal, half the daughters would be carriers and half the sons would be affected

23
Q

If an affected male of an X-linked recessive inheritance disease and a normal female bred, what phenotypes would there offspring be?

A

All the daughters will be carriers and none of the sons will be affected

24
Q

What are examples of X chromosome sex-linked dominant diseases?

A

Incontinentia pigmenti, Charcot-Marie tooth neuropathy, Coffin-Lowry syndrome and Hypophosphatemic rickets

25
Q

What are examples of Y chromosome sex-linked dominant diseases?

A

Unknown

26
Q

If an affected male of an X-linked dominant inheritance disease and a normal female bred, what phenotypes would there offspring be?

A

All the daughters will be affected and none of the sons will be affected

27
Q

If an affected female of an X-linked dominant inheritance disease and a normal male bred, what phenotypes would there offspring be?

A

Half of the males and females would be normal whilst the other half of both the males and females would be affected

28
Q

What can be ruled out if two affected parents have unaffected children?

A

Recessiveness (True for both autosomal and sex-linked traits)

29
Q

What can be rules out if unaffected parents have an affected child?

A

Dominance (True for both autosomal and sex-linked traits)

30
Q

What can be ruled out if unaffected parents have an affected daughter?

A

Dominance and X-linked recessive

31
Q

What can be ruled out if an affected woman has an unaffected son, OR an unaffected man has an affected daughter?

A

X-linked recessive

32
Q

What can be ruled out if an unaffected woman has an affected son, OR an affected man has an unaffected daughter?

A

X-linked dominance

33
Q

If a woman’s brother has died from Tay Sach’s Disease (autosomal recessive, lethal), but she is unaffected, what are the chances that she is a carrier?

A

2/3

34
Q

Assuming your Grandfather A is a carrier of an allele for a rare autosomal recessive disease, what’s the chance that YOU are also a carrier of this allele?

A

25%

35
Q

Name two molecular markers?

A

SSR and SNP

36
Q

What is SSR?

A

Simple Sequence Repeats
Microsatellites (2-4 basepair repeats)
Minisatellites (variable number tandem repeats or short tandem repeats)

37
Q

What is SNP?

A

Single Nucleotide Polymorphisms

38
Q

In SSR what do more sequence repeats equal?

A

Bigger PCR product

39
Q

In SSR what do fewer sequence repeats equal?

A

Smaller PCR product

40
Q

How does linkage mapping in SSRs take place?

A
  1. Collect pedigree information from a family with history of a genetic disease, and also blood samples for DNA from living family members
  2. Use PCR and gel electrophoresis to determine genotype of family members for several hundred SSR loci distributed throughout the genome (many on each chromosome)
  3. Use statistical linkage analysis to identify SSRs that are linked (low recombination) to inheritance of the disease allele (defining a mapping interval or locus)
  4. Identify new molecular markers from within the locus, and repeat the linkage analysis with additional families to resolve a narrower map interval

LF104: Molecules, Cells And Organisms (33 decks)

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