007 CAL pedigree analysis Flashcards
what is a nuclear family?
- A traditional nuclear family consists of a married couple and their biological child or children
- A child in a traditional nuclear family lives with both biological parents, if siblings are present, only full brothers and sisters (that is, siblings who share the same two biological parents).
what type of family is this pedigree?
nuclear family (married couple and their own child)
which of these pedigrees shows a nuclear family?
2
in a pedigree what does circle/square/diamond mean?
- circle = woman
- square = man
- diamond = unknown gender
in a pedigree, what does white/black/ half and half coloured in mean/
- white = unaffected
- black = affected
- half and half = heterozygous carrier
in a pedigree what does a line through the square/circle mean?
- deceased
what does 2 lines between partners mean in a pedigree?
consanguineous relationship (related partners)
Pedigree attached, jonathon and maria have an autosomal recessive disease that affects 1 newborn in 11,000. Assuming it is 100% penetrance, what is the expected frequency of carriers of the disease?
- 0.019
- genotype frequency is aa (homozygous recessive) which is q^2 = 1/11,000
- so q = 0.0095
- p + q = 1
- so p = 0.9905
- so carrier frequency = 2pq = 0.019
what is the Hardy-Weinburg equation?
p^2 + 2pq + q^2 = 1
and
p + q = 1
what is p^2 in the Hardy-Weinburg equation?
- frequency of homozygous dominant alleles
what is q^2 in the Hardy-Weinburg equation?
- frequency of homozygous recessive alleles
what is 2pq in the Hardy-Weinburg equation?
- frequency of heterozygous carrier alleles
what is p in the Hardy-Weinburg equation?
- the frequency of dominant allele A (just 1)
what is q in the Hardy-Weinburg equation?
- the frequency of recessive alleles a (just 1)
this pedigree is autosomal recessive with 100% penetrance, what is the probability that Elizabeth is a heterozygous carrier?
- 2/3
- she is not affected and it is 100% penetrance so she cannot be aa
- the options left from punnet square is AA, Aa, Aa, (as parents must be Aa, Aa) so carrier probability is 2/3
about 7% of men are colourblind due to X-linked recessive gene, what proportion of women are expected to be carriers?
- 0.13
- frequency of affected males = 0.07 = q ( men only carry 1 X chromosome)
- so p = 1-q so p = 0.093
- so carriers = 2pq = 0.13
about 7% of men are colourblind due to X-linked recessive gene, what proportion of women are colourblind?
- 0.0049
- frequency of affected males = 0.07 = q ( men only carry 1 X chromosome)
- frequency of affected females = q^2 = 0.0049 ( women have 2 X chromosomes)
what is the most likely mode of inheritance from this pedigree?
- X-linked recessive
- usually, it is only sons affected, transmitted from the mother
- however as the last generation is consanguineous, both parents carry the allele, thus their daughter can also be affected
a man affected with an X-linked recessive disorder marries a healthy female (homozygous).
what proportion of their sons and daughters will be affected?
- 0% sons and 0% daughters
- man doesn’t pass on X chromosome to son
- daughters will be carriers but not affected (only 1 recessive)
what is the most likely mode of inheritance in this pedigree?
- autosomal dominant
- could also be X-linked dominant but this is much rarer and are often lethal
why is this pedigree not mitochondrial inheritance?
- because not all children are affected from affected mother and there is father transmission (only mothers can pass on)
steve has an autosomal recessive condition that affects 1 child in 3500 in the UK, what is the frequency of carriers in the population?
- 0.033
- q^2 = 1/3500
- so q = 0.0169
- p = 1- q
- carrier frequency = 2pq = 0.033
