100 Mendelian and Human Genetics Exercise E: Pedigree Analysis ing pure lines. N
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100 Mendelian and Human Genetics Exercise E: Pedigree Analysis ing pure lines. Neariy Mendel's success was in part due to the pea plants' ability to self-pollinate, creat all animals are incapable of self-fertilization. This makes understanding the genetics of an humans) increasingly more complicated than plants imals (like ies contemporar Pedigree analysis is a method that uses the principles developed by Mendel and his to look at families' genetic histories with an attempt to understand how phenotypes are ex a pedigree, squares represent males and circles represent females (Fig. 3). Horizontal lines a mating event producing children. Children are connected to their parents' horizontal line by a vertical line and are shown below their parents. Generations are shown with Roman nu pressed. In (i.e. I, y inherited trait, which is merals I., Il,etc.). Pedigree analyses are typically used to follow a specific geneticall customarily shaded. 20. What is the probable genotype(s) of the the man identified as 27 How do you know? 8 21. What is the probable genotype(s) of the man identified as 9? How do you know? 9 (10 Fig. 5. A simple pedigree. An analysis of a recessive autosomal trait: sickle-celled anemia Let's look at a pedigree analysis for an autosomal (that is, not sex-linked) recessive phenotype, sickle- celled anemia. Blood shape is determined by a single gene. Normal blood cells are donut-shaped and last in the human body approximately 120 days, and are coded for by a dominant allele (expressed by the genotypes BB or Bb. Humans with sickled-celled anemia have crescent-shaped blood cells that only last 10 days, and therefore must produce approximately 12 times the number of blood as a person with normal blood shape. This hyperproduction of blood cells requires a tremendous amount of the extremely limited essential element, iron. Sickled-celled humans are usually depleted of iron, causing them to be anemic (iron-deficient). You may be wondering how can a phenotype that lowers a human's fitness to such a degree persists through the generations based on the principles of natural selection. It turns out that the sickled-blood cell phenotype originated in equatorial Africa (and is most common in people with Sub-Saharan African descent). It has been discovered that people with sickled cells tend to have a natural immunity to the malaria parasite, so common in equatorial regions. Therefore, it may have been more beneficial for ancestral Sub-Saharan Africans to be anemic if they did not suffer the consequences of malaria. www.thebiologyprimer.comExplanation / Answer
Sickle cell anaemia is an autosomal recessive disease. It means the probability of criss cross or y linked inheritance is ruled out. Also due to its recessive nature, both the alleles for the gene need to be mutated for the person to be diseased.
(bb)- diseased , both recessive
(BB)-both dominant, healthy
(Bb)- disease free but carrier for sickle cell anaemia.
Now If you analyze, Person 1 , 10 and 11 are diseased. All are (bb)
Start from Generation I- 1 has both alleles mutated. It means she will transfer a defected allele to all the children in her progeny with 100% probability.
All the children are disease free and hence 3,4 and 5 are Bb
Now come to their Father. He is disease free. Hence not bb. But there are equal chances that he might be Bb or BB. None of his children 3,4, and 5 inherited his defected allele; if he carries any.
Generation II- 5 marries 6. None of the Two children they bear are diseased. Hence none is bb.
There is 50% chance that they inherited a defected allele from their father, but the possibilty of 6 being Bb cannot be ruled out either. She can be BB or Bb. Their children can be Bb or BB.
Generation III- 2 out of 4 children of Person 8 are diseased. It means he transferred the defective allele to them. 8 is Bb. To be diseased, the genotype should be bb which is possible only when 7, their mother is a carrier. It means she is Bb.
Generation IV-10 and 11 are diseased and there is 50-50 chances that 12 and 13 are either BB or Bb. But they surely did not inherit the mutated allele from both the parents as they are disease free.
Summarising- 1- (bb), 2- (Bb) or (BB) 3 & 4- (Bb) or (BB)
5-(Bb) 6-(Bb) or (BB) 7&8- (Bb) 9- (Bb) or (BB)
10 & 11 (bb) 12 & 13 (BB) or (Bb)
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