Pedigrees Notes Genetics, Lecture notes of Genetics

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Chapter 6

Pedigrees

observing patterns in inheritance

Waardenburg syndrome

characterized by

deafness, fair skin, visual

problems, and a white

forelock.

P= Proband Inherited as a single-gene trait

Dominant Autosomal Conditions Huntington's Disease 4p Marfan Syndrome 15q Achondroplasia 4p Juvenile Osteoporosis 7q Familial ALS (Amyotrophic lateral sclerosis) different genes involved, some dominant

Hyperinsulinaemic Hypoglycaemia (HH) high secretion of insulin from pancreas causes low blood sugar 3 different families carrying different mutations in the ABCC8 gene encoding sulfonylurea receptor 1 Kapoor, Flanigan et al. Diabetologia 2011 -Never skips a generation -Affected persons have as least one affected parent -Appear with equal frequency in men and women -Approximately ½ of each generation afflicted, assuming afflicted people are heterozygous due to low frequency Autosomal Dominant Trait

What is the genotype of the circled individual (dominant allele - A)?

1. AA
2. AA or Aa
3. Aa
4. aa

Autosomal Recessive Conditions Cystic fibrosis Sickle Cell Anemia Tay Sachs Phenylketonuria Albinism Am J Hum Genet. 1962 December; 14(4): 391– -Tend to skip generations -Usually appears with equal frequency in men and women -More likely to appear among progeny of related individuals Hopi OCA2 1:200 incidence vs 1:20,

aa aa aa aa

Can infer heterozygous carriers

Aa Aa

Pedigree of Autosomal Recessive Trait unaffected could be a carrier Note:assume incoming mates are not carriers as a first try if trait is “rare”

consanguinity

consanguinity

33 million ancestors

if no overlap

you Ancestor Paradox

Some shared alleles are expected

in a local population due to shared ancestors

20 generations

~500 years ago

e.g. Cystic Fibrosis in Northern European population 1/25 are carriers 80% are same one mutation

23andMe results- distant relations Share 1/ Share 1/ Share 1/

Draw to Understand-Pedigrees 1a. What type of inheritance does the above rare early onset Alzheimer’s pedigree display in generations I, II and III?

The inherited Alzheimer’s trait does not appear until middle age and the individuals in generation IV are not old enough to know if they have the trait (thus the ?). a. What is the probability that individual IV-1 will develop early Alzheimer’s?

b. What is the probability that a mating between IV-2 and IV-3 would produce a child who would later develop the trait? __________________ due next Wednesday 11:59 pm

Draw to Understand-Pedigrees R r

R RR Rr

r Rr rr