Human Pedigrees

Question 1

What are some of the symbols used in human pedigrees

Answer 1

square - male
shaded in square - male with disease
circle - female
shaded circle - female with disease

two lines - consangenous marriage (genetic nightmare)

individuals marrying into the family are assumed homozygous normal unless stated otherwise

Question 2

What are mendelian genetics

Answer 2

some mendelian genetics are inherent to human diversity and others such as mendelian disorders are rare, they are inherited disorders such as chronic grandulomatose disease, marfan syndrome, haemophilia, hammamy syndrome and albinism

Question 3

What are pedigrees

Answer 3

pedigrees are collections of human families where a mutation causing a dominant or recessive trait is segregated.

samples of the disease is small so is unlikely to show mendelian genetics

Question 4

What are autosomal recessive disorders

Answer 4

• autosomal recessive disorders appears in progeny of unaffected parents, male and female in affected progeny inheritance of an autosomal dominant disorder

Question 5

What is an example of an autosomal recessive disorder

Answer 5

dwarfism
- pseudoachondroplasia: a dominant allele interferes with the growth of the long bones mutation in COMP gene, causes a dominant allele, two copies are lethal so always heterozygous for the dominant allele
- pedigree shows affected males and females in every generation, shows affected men and women transmitting condition to equal proportion of sons and daughters

Question 6

What is the inheritance of an X-linked disorder

Answer 6

• shows only males are affected and one generation is not affected
• assume one person is heterozygous for a rare genetic recessive disorder, would be unlikely

in a dominant disorder if everyone affected comes from one affected parent
- it will be an X-linked autosomal disorder

Question 7

What are the steps for calculating genetic risk

Answer 7

i. determine the mode of inheritance of the trait (recessive/dominant - autosomal/X-linked)
ii. assign genotypes and probabilities to paternal individuals in pedigree
iii. calculate final probabilities applying theoretical mendelian ratios