GENETICS MAJORS ONLY PLEAASEE The pedigree in Figure 5.9 in Lewis is for a mitoc
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GENETICS MAJORS ONLY PLEAASEE
The pedigree in Figure 5.9 in Lewis is for a mitochondrial gene. If it was for an X-linked gene, can you determine whether or not it is dominant or recessive? Why or why not? Make sure to use examples from the pedigree to support your answer. (5 marks)
10 3 9 10 11 12 13 14 15 Figure 5.9 inheritance of mitochondrial genes. Mothers pass mitochondria genes to all offspring. Fathers do not transmit mitochondrial genes because sperm only very rarely contribute mitochondria to fertilized ova. If mitochondria from a male do enter, they are destroyed.Explanation / Answer
According to the information, the disease is mitochondrially inherited in the pedigree. However, if the disease is inherited as an X-linked disorder, it can be either dominant or recessive in nature. In order to identify the nature of inheritance, it must be acknowledged that human males are heterozygous (XY) for allosomes whereas human females are homozygous (XX). This means that if any disease is inherited in X-linked recessive manner, then it will affect the males whenever the X-chromosome carries the allele whereas it can affect the females only if they are homozygous for the alleles. In that scenario, the females will be only carrier.
On the other hand, if a disease is inherited in dominant manner, then the males as well as females will be affected by the disease as even the single allele will be able to express itself.
Thus, keeping this information in mind, it should be carefully noted that the parents carry a trend in which the male is not affected but the female is affected (parental class). This must also be observed that this affected female is able to transmit this disease to all of her sons and daughters (in F1 generation). Now at this point, the disease can be X-linked recessive as well as dominant in nature.
Now look at the pedigree in generation 2 (FII generation). It can be clearly noticed that the individual II-2 (a male) is not affected by the disease but the individual II-4, 5 and 6 all are affected by the disease. The difference here is that the father of individual II-2 carried and allele for sure but the mother of individuals II-4, 5 and 6 was also affected. This suggests that the allele which the father transmitted to the daughters (II-1, 3) was recessive in nature and showed a maternal pattern of inheritance. It cannot be directly stated whether the allele was dominant or recessive in nature because even if the mother passed a single X-linked allele to daughters, they were affected by the disease.
Thus, it is likely that the gene is X-linked dominant in nature but relies upon maternal pattern of inheritance in these generations.
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