L18- Inheritance review questions Flashcards
The ability to taste phenylthiocarbamide (PTC) and propylthiouracil (PROP) is mainly determined by one gene called TAS2R38, and is inherited in an autosomal dominant manner. For simplicity, let us assume two alleles: a ‘taster allele’ and a ‘non-taster allele’. Non-tasters are homozygous for the ‘non-taster allele’, while tasters can be heterozygous or homozygous. A study suggests the non-taster allele frequency is 6 in 10, and the taster allele frequency is 4 in 10.
What is the expected ratio between non-tasters and tasters?
Non-tasters will have two recessive alleles, both with a frequency of 0.6, therefore non-tasters are expected to be found at a frequency of 0.6x0.6= 0.36 (i.e. 36% of all individuals of a given population are expected to be non-tasters).
Tay-Sachs disease shows autosomal recessive inheritance. A couple, in whose families the disease is not known to have occurred previously, have one affected child and two who are normal. The husband’s sister wishes to marry the wife’s brother.
What is the risk that the first child of this second couple will be affected with the disease?
NB. Assume that the recessive allele is very rare in the population.
HINT: You may want to draw a pedigree to help you answer the question.
what does it mean when two genes are linked
When 2 genes are linked they are found on the same chromosome e.g. X chromosome
If 2 genes are on the same chromosomes alleles will travel together in meiosis (usually without
crossing over)
