Mendelian genetics 1

Question 1

are most cells haploid or dipoid?

Answer 1

diploid (two homologous copies of each chromosome)

Question 2

what is the difference between genotype and phenotype?

Answer 2

genotype = genetic constitution 
phenotype = physical appearance

Question 3

most cases of an autosomal dominant disease are what?

Answer 3

most often heterozygous
can have homozygotes, but they are at a selective disadvantage relative to heterozygous and frequently die before reproductive maturity

Question 4

Family hypercholesterolaemia what form of genetic disease?

Answer 4

it is an autosomal dominant disease
those heterozygous for it = have elevated LDL and have MI 30-40 years

those homo for it = 10X normal blood LDL and have fatal MI in childhood

Question 5

what is the standard AD inheritance pattern?

Answer 5

1) vertical
2) both sexes have an equal probability of being affected
3) both sexes will transmit the mutation = affected
4) approx. 50% of offspring of an affected parent will be affected

Question 6

how does a mutation at a single gene cause a disease phenotype?

Answer 6

Haploinsufficiency - where the normal physiology requires more than 50% gene functionality - therefore one mutation in an allele is enough to affect the patient

Dominant negative effect = abnormal protein interferes with the function of the normal protein

Gain of function = function of mutant protein enhances, or novel protein is toxic

loss of heterozygosity = inherited copy of mutant gene and loss of normal allele, even in only a few cells, renders those cells cancerous

Question 7

what are the characteristics of autosomal recessive inheritance?

Answer 7

1) symptoms are seen only in recessive homozygotes
2) heterozygotes are said to be carrier’s of the mutation
3) carriers are not at a selective disadvantage

Question 8

what type of inheritance does cystic fibrosis follow?

Answer 8

autosomal recessive