Genetics - Analysis and Principles

Biology

Quiz 4 :

Extensions of Mendelian Inheritance

Quiz 4 :

Extensions of Mendelian Inheritance

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The blood serum from one individual (let's call this person individual 1) is known to agglutinate the red blood cells from a second individual (individual 2). List the pairwise combinations of possible genotypes that individuals 1 and 2 could be. If individual 1 is the parent of individual 2, what are his or her possible genotypes
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ABO blood group alleles can be dominant, recessive, or co-dominant:
The red blood cells of plasma membrane contain sugars that are interconnected on the surface of antigens. An antigen acts as molecular structures that are recognized by the antibodies of immune system. The two type of antigens present are A and B. The surface antigen synthesis is regulated by the alleles of I A and I B. However, i allele is recessive to both I A and I B. In humans, ABO blood group type antigens are an example of multiple alleles, which determines blood type in humans. Moreover, it illustrates the allelic relationship of co-dominancE.The following diagram depicts the alleles of ABO blood groups:
img When serum from individual 1 agglutinates red blood cells from individual 2, the possible genotypes could be:
• If individual 1 is ii , individual 2 could be I A i, I A I A ,I B i, I B I B , or I A I B.
• If individual 1 is I A i or I A I A , individual 2could be I B i, I B I B ,I B i or I A I B.
• If individual 1 is I B i or I B I B , individual 2could be I A i, I A I A or I A I B.
For instance, on assuming individual 1 is the parent of individual 2.
• If individual 1 is ii , individual 2 could be I A i or I B i.
• If individual 1 is I A i , individual 2could be I B i or I A I B.
• If individual 1 is I A I A , individual 2could be I A I B.
• If individual 1 is I B i, individual 2could be I A i, or I A I B.
• If individual 1 is I B I B , individual 2could be I A I B.

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Mexican hairless dogs have little hair and few teeth. When a Mexican hairless is mated to another breed of dog, about half of the puppies are hairless. When two Mexican hairless dogs are mated to each other, about 1/3 of the surviving puppies have hair, and about 2/3 of the surviving puppies are hairless. However, about two out of eight puppies from this type of cross are born grossly deformed and do not survive. Explain this pattern of inheritance.
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Typically Mexican hairless dogs that have little hair and few teeth are heterozygous for a dominant allele. These genes are lethal when occur in homozygous condition. When two Mexican hairless dogs were mated to each other, we can expect 50% of the total offsprings to be hairless, 25% offsprings to be normal, whereas 25% offsprings diE.

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In oats, the color of the chaff is determined by a two-gene interaction. When a true-breeding black plant was crossed to a true-breeding white plant, the F 1 generation was composed of all black plants. When the F 1 offspring were crossed to each other, the ratio produced was 12 black to 3 gray to 1 white. First, construct a Punnett square that accounts for this pattern of inheritance. Which genotypes produce the gray phenotype Second, at the level of protein function, how would you explain this type of inheritance
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The 12:3:1 ratio suggests that this is dominant epistasis cross. Begin by assuming that black is dominant over some unknown color, and black must be expressed before an allele in Gene 2.
Step 1: Designate the alleles:
Gene 1
Black chaff: B
Unknown color chaff: b
Gene 2
Gray chaff: G
White chaff: w
Step 2: Construct a Punnett square.
Add the phenotypes to each combination to see if the inheritance pattern gives 12:3:1 ratio specified in the problem.
img Step 3: Analyze this type of inheritance pattern.
From the Punnett square, we see that the data fit our original assumption and reveal the genotype that produced the gray phenotype.
Step 4: Analyze this type of inheritance pattern at the level of protein function.
Dominant epistasis involves the interaction of genes. The proteins produced by these genes can interact with one another. For example, the protein encoded by one gene can modify the protein encoded by another gene.
Another possibility is that two different proteins may act in unison to get a certain reaction. If only one protein is present, a certain biochemical reaction occurs, but if two link up, the resulting reaction might occur differently or not at all. In any case, such interactions can do change the patterns of inheritancE.

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In chickens, some varieties have feathered shanks (legs), but others do not. In a cross between a Black Langhans (feathered shanks) and Buff Rocks (unfeathered shanks), the shanks of the F 1 generation are all feathered. When members of the F 1 generation are crossed to each other, the F 2 generation contains chickens with feathered shanks to unfeathered shanks in a ratio of 15:1. Suggest an explanation for this result.
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A true-breeding rooster with a rose comb, feathered shanks, and cock-feathering was crossed to a hen that is true-breeding for pea comb and unfeathered shanks but is heterozygous for hen-feathering. If you assume these genes assort independently, what is the expected outcome of the F 1 generation
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An allele in Drosophila produces a "star-eye" trait in the heterozygous individual. However, the star-eye allele is lethal in homozygotes. What would be the ratio and phenotypes of surviving flies if star-eyed flies were crossed to each other
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What is meant by a gene interaction How can a gene interaction be explained at the molecular level
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Which blood phenotypes (A, B, AB, and/or O) provide an unambiguous genotype Is it possible for a couple to produce a family of children with all four blood types If so, what would the genotypes of the parents have to be
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Duroc Jersey pigs are typically red, but a sandy variation is also seen. When two different varieties of true-breeding sandy pigs were crossed to each other, they produced F 1 offspring that were red. When these F 1 offspring were crossed to each other, they produced red, sandy, and white pigs in a 9:6:1 ratio. Explain this pattern of inheritance.
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Describe the differences among dominance, incomplete dominance, codominance, and overdominance.
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The Mic2 gene in humans is present on both the X and Y chromosome. Let's suppose the Mic2 gene exists in a dominant Mic2 allele, which results in normal surface antigen, and a recessive mic2 allele, which results in defective surface antigen production. Using molecular techniques, it is possible to identify homozygous and heterozygous individuals. By following the transmission of the Mic2 and mic2 alleles in a large human pedigree, would it be possible to distinguish between pseudoautosomal inheritance and autosomal inheritance Explain your answer.
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In sheep, the formation of horns is a sex-influenced trait; the allele that results in horns is dominant in males and recessive in females. Females must be homozygous for the horned allele to have horns. A horned ram was crossed to a polled (unhorned) ewe, and the first offspring they produced was a horned ewe. What are the genotypes of the parents
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As discussed in this chapter, comb morphology in chickens is governed by a gene interaction. Two walnut comb chickens were crossed to each other. They produced only walnut comb and rose comb offspring, in a ratio of 3:1. What are the genotypes of the parents
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Let's suppose a gene exists as a functional wild-type allele and a nonfunctional mutant allele. At the organism level (i.e., at the level of visible traits), the wild-type allele is dominant. In a heterozygote, discuss whether dominance occurs at the cellular or molecular level. Discuss examples in which the issue of dominance depends on the level of examination.
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A particular breed of dog can have long hair or short hair. When true-breeding long-haired animals were crossed to true-breeding short-haired animals, the offspring all had long hair. The F 2 generation produced a 3:1 ratio of long- to short-haired offspring. A second gene affects the texture of the hair. The two variants are wiry hair and straight hair. F 1 offspring from a cross of these two varieties all had wiry hair, and F 2 offspring showed a 3:1 ratio of wiry-haired to straight-haired puppies. Recently, a breeder of the short-, wiry-haired dogs found a female puppy that was albino. Similarly, another breeder of the long-, straight-haired dogs found a male puppy that was albino. Because the albino trait is always due to a recessive allele, the two breeders got together and mated the two dogs. Surprisingly, all of the puppies in the litter had black hair. How would you explain this result
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A nectarine is a peach without the fuzz. The difference is controlled by a single gene that is found in two alleles, D and d. At the molecular level, would it make more sense to you that the nectarine is homozygous for a recessive allele or that the peach is homozygous for the recessive allele Explain your reasoning.
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In the clover butterfly, males are always yellow, but females can be yellow or white. In females, white is a dominant allele. Two yellow butterflies were crossed to yield an F 1 generation consisting of 50% yellow males, 25% yellow females, and 25% white females. Describe how this trait is inherited and specify the genotypes of the parents.
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Let's suppose a recessive allele encodes a completely defective protein. If the functional allele is dominant, what does that tell you about the amount of the functional protein that is sufficient to cause the phenotype What if the allele shows incomplete dominance
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A seed dealer wants to sell four-o'clock seeds that will produce only a single color of flowers (red, white, or pink). Explain how this should be done.
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Discuss the differences among sex-influenced, sex-limited, and sex-linked inheritance. Give examples.
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