Question

Huntington’s disease: Huntington’s disease is a disease in which certain parts of the brain waste away; symptoms usually begin later in life. In a community in Venezuela, an allele for Huntington’s disease (represented by the letter H) is completely dominant to the allele for no Huntington’s disease (represented by a lowercase h). The three possible parental genotypes are HH, Hh, and hh. There are six possible crossings that can be made between these genotypes (for example, HHxHH, HHxHh, etc.). Show the probabilities of the genotypes and phenotypes in the F1 generation from all six possible crossings. In real human families, would you see offspring in proportions equivalent to these probabilities? Why or why not?

Answer 1

Regarding Huntington's disease, it can be said that it is an inherited disease with an autosomal dominant character, so it is enough that one of the children inherits one of these characters to manifest this neurodegenerative disease, it is considered that the pattern is usually 50% of the total of children of sick parents can suffer it, however if both parents are carriers the number rises leading to 100% of the children affected, on the contrary if no parent has the dominant gene and are homozygous recessive, neither your children will suffer the disease

The possibilities are the following:

Parent 1, inheritance pattern: Hh * hh, the possible gametes for this cross-linking are H, H, h, h, offspring; Hh, Hh, hh, hh 50% of the children could be sick

Parents 2, inheritance pattern: hh * hh, the possible gametes for this cross-linking are h, h, h, h. the offspring will be; hh, hh. no sick child

Parent 3, inheritance pattern: HH * HH, the possible gametes for this cross-linking are H, H, H, H, the offspring will be HH, HH, all children may be sick, 100%

parents 4, inheritance pattern: Hh * Hh, the possible gametes for this cross-linking are h, H, h, H. the descendants will be HH, Hh, Hh, hh 50% of sick children

Parents 5, inheritance pattern: Hh * hh, the possible gametes for this interbreeding are H, h ,, offspring will be Hh all sick children

Parent 6, inheritance pattern: Hh * Hh the possible gametes for this cross-linking are H, h, the descendants will be Hh, the heterozygous descendants will have the disease.