When determining the mode of inheritance in a family a pedigree and be used. A Pedigree is a diagram which shows the presence or absence of a heritable trait through a family for several generations. Five modes of inheritance that will be tested are autosomal dominant, autosomal recessive, sex-linked dominant, sex-linked recessive, and Y-linked.
A shaded square or circle indicates the presence of a trait, an unshaded square or circle indicates the absence of a trait. Circles represent female individuals while squares represent male individuals. A horizontal line indicates a mating and a vertical life indicates offspring.It can be immediately assumed that the trait is not Y-linked because individual 8 is female. Therefore, she would not have a Y chromosome where, in theory, the gene would be located if it was a Y-linked gene. For generations I and II it would seem possible for the trait to be Y-linked because up until that point it is only depicted in males. However the presence of the trait in a female (individual 8, generation III) disproves the theory.Autosomal dominant is a possible mode of inheritance because if individual 1 is heterozygous and individual 2 is homozygous recessive, then individuals 3 and 4 would be able to inherit two recessive copies of the allele, explaining why they are unaffected, while individual 5 would be inherit one dominant copy of the allele and one recessive copy, explaining why individual 5 is affected.
Since individual 5 is heterozygous, individual 8 would also be heterozygous because they must have inherited the dominant allele from their father and a recessive allele from their mother (individual 6), which would explain why individuals 7 and 9 are not affected by the trait.Autosomal Recessive is a possible mode of inheritance assuming that individuals 1, 5, and 8 are all homozygous recessive and that all other individuals shown (2,3,4,6,7, and 9) are heterozygous. They would have to be heterozygous in order for the individuals who are homozygous recessive to have been able to inherit two copies of the recessive allele, thus expressing the trait.Sex-linked dominant is not a possible mode of inheritance because individual 1 has one X chromosome and one Y chromosome.
Since Y chromosomes are only present in males, individual 1 would need to have a recessive version of the allele on his Y chromosome in order to have male offspringwithout the trait. The presence of the recessive allele on the Y chromosome leads to the assumption that the individual’s X chromosome must carry the dominant version of the allele in order for him to have the trait. This becomes an issue when one takes into consideration that female offspring receive an X chromosome from their mother and an X chromosome from their father, it has already been determined that individual 1 has a dominant allele on his X chromosome, his daughter (individual 4) would have inherited a dominant copy of the allele, which is impossible because she does not express the trait.Sex-Linked RecessiveSex-linked recessive is a possible mode of inheritance because individual 1 would have a recessive allele on both is Y and X chromosome. Despite the fact that all of his children inherited a chromosome from him only one of them displays the the trait (individual 5), this is because it can be assumed that his mother (individual 2) is heterozygous for the trait, meaning that she carries one dominant and one recessive copy of the allele.
Individuals 3 and 4 do not display the trait because they inherited their mother’s X chromosome with the dominant version of the allele, causing the recessive trait not to be expressed. On the other hand, individual 5 does express the trait, meaning it he inherited two copies of the recessive allele (one from each parent), thus proving his other (individual 2) is heterozygous for the trait, as opposed to being homozygous dominant.After testing five modes of inheritance, autosomal dominant, autosomal recessive, sex-linked dominant, sex-linked recessive, and Y-linked, it was determined that autosomal dominant, autosomal recessive, and sex-linked recessive are all possible modes of inheritance for the depicted trait. It was also determined that Y-linked and sex-linked dominant were not possible modes of inheritance for the given trait. This conclusion was reached by considering the phenotypes of the individuals and assigning them possible genotypes based on the mode of inheritance being tested for.