1. Interactions among the human ABO blood group alleles involves both and 2. Two
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1. Interactions among the human ABO blood group alleles involves both and 2. Two tauntauns are crossed. One tauntaun is true breeding for fur that has a grey color, and the other is true breeding for fur that is white. The offspring of this cross have fur that ranges between white and grey, with many intermediate colors. If fur color is determined bya single gene, what type of dominance is seen? 3. The allele for human polydactyly is a dominant allele. Some people that carry the allele do not display the characteristic at all. When some organisms in the population that possess a dominant allele for a simple dominant/recessive trait do not express the trait this means thatExplanation / Answer
1. The ABO system of blood grouping depends on the expression of A and B surface antigens on surface of red blood cells. The A and B antigens are carbohydrate moieties. Presence of A antigens means that blood group is A. If B antigens are present, then the blood group is B. If both A, and B are present, AB is the blood group. If A and B are absent, the blood group is O. There is another protein present on RBCs. It is the Rhesus factor or Rh factor. Presence of Rh factor is denoted by + sign while absence of Rh factor is denoted by – sign. Hence, there are eight blood groups: A Rh+, A Rh-, B Rh+, B Rh-, AB RH+, AB Rh-, 0 Rh+, or 0 Rh- .
In incomplete dominance, neither of the two alleles are dominant. However, they combine and display a trait that is a mixture of the two allele. In co-dominance, both alleles are equally dominant. Hence, the heterozygous phenotype has the expression of both allele equally.
In ABO blood grouping, A and B allele are co-dominant allele. However, they are both dominant over ) allele, which is a recessive. Hence, ABO interactions involves co-dominance and complete dominance.
Right answer: co-dominance; complete dominance.
2. Let the two allele for fur gene be F and f. The true breeding tauntaun for grey color will be FF and for white is ff. Cross between them give Ff heterozygous offsprings. If it was complete dominance, the Ff offspring would have a grey color. However, the fur colors are ranging between white and grey. This is incomplete dominance as the colors are a mixture of white and grey. If it was co-dominance, only grayish white offsprings would be seen.
Right answer is incomplete dominance.
3. Polydactyl is presence of extra fingers and/or toes in humans. It is an autosomal dominant trait and should be seen in only 50% of the children of a person with polydactyl. However, some people never express the trait despite having the allele. This allele may be transferred to their children who mat express the trait. This is due to differences in` penetrance of the trait. Expressivity describes the situation where the gene is dominant but not expressed equally in the individuals that carry them. There is incomplete penetrance of the dominant
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