Inheritance and genetic problems
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Which describes two genes at different loci on the same chromosome?
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They are linked.
Crossing-over can alter how strongly their inheritance is associated.
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Which tester is used to reveal gametes from AaBb?
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aabb
Its recessive alleles make the heterozygote's contributions visible in offspring phenotypes.
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How many ABO alleles does an IA IB individual normally carry?
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Two
Three main alternatives exist in the population, but this individual has IA and IB.
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P(affected | son) = 1/2 and P(son) = 1/2. What is P(affected son)?
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1/4
1/2 x 1/2 = 1/4 of all offspring.
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In a pedigree, two unaffected parents have an affected daughter and an unaffected son. Which mode of inheritance fits this family best?
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Autosomal recessive
Unaffected parents with an affected child show the allele is recessive. An affected daughter of an unaffected father rules out X-linked recessive, so it is autosomal.
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Two parents are both carriers (Aa) of an autosomal recessive condition. Their unaffected daughter is shown in the pedigree. What is the probability that she is a carrier?
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2/3
Being unaffected excludes aa, leaving AA, Aa and aA in equal shares. Two of these three are carriers.
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Which are recombinant gametes from an AB/ab parent?
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Ab and aB
These combine alleles from different original homologues.
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A test cross of AaBb x aabb gives AB 410, ab 390, Ab 105, aB 95. Which conclusion is best supported?
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A and B are linked, about 20 map units apart.
Parental classes far outnumber recombinants: (105 + 95) / 1000 = 20% recombination, so the genes are linked.
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Which genotype is brown in the stated two-step pathway?
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Aabb
A produces the brown intermediate, but bb blocks its conversion to purple.
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Which ratio from AaBb x AaBb is NOT explained by epistasis?
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1:1:1:1
That is the test-cross ratio for AaBb x aabb. Epistasis merges classes of 9 : 3 : 3 : 1 into fewer groups.
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What does queen/worker differentiation illustrate?
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An environmental input can influence gene expression and phenotype.
Developmental nutrition affects the pathway taken by genetically capable larvae.
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