Question 1

A tomato plant with large leaves and round fruits was crossed to a plant with small leaves and oblong fruits.The F₁ consisted of plants with large leaves;about half of these plants made round fruits and the other half made oblong fruits.Two F₁ plants (one with round fruits and one with oblong fruits)were then analyzed through further crossing.The results were: a)What are the genotypes of the two original parents? b)What are the expected phenotypic ratios in the progeny of a cross between "F₁ plant #1" and a tester? c)What gamete genotypes can "F₁ plant #2" produce? Explain your reasoning behind each of your answers.

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Question 2

Two albino strains of Neurospora crassa were isolated in two different laboratories.When either one was mated with wild type (orange)it produced 1/2 albino: 1/2 orange progeny.
a)What can you now deduce about the genetics of each of these albino strains?
b)Assume first that the two strains carry allelic mutations.Using appropriate symbols,diagram a cross of the two albino strains.Include the genotypes of the parents,a stick-and-circle diagram of the relevant chromosomes at metaphase I of meiosis,and the genotypes and ratios of the progeny.
c)Now assume that the two strains carry mutations in different genes,and that the genes are on different chromosomes.Answer the same questions as above.Assume that there are no crossovers between either gene and the centromeres.

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Question 3

If stem length in a certain species of crops was solely determined by polygenic inheritance,how many different genes would be required in this system to explain the existence of 15 different stem lengths ranging from 15 to 29 cm?

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Question 4

A woman with tritanopia (a rare form of inherited blue-yellow color blindness)marries a man who also has tritanopia.Their first daughter has normal color vision but is diagnosed with PKU.
a)Based on this information,what is the most likely mode of inheritance of tritanopia?
b)Using symbols of your own invention,write the genotypes of the two parents and of their daughter.(Assume independent assortment.)
c)What is the probability that the couple's next child is a son with tritanopia and PKU? (Assume independent assortment.)

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Question 5

Vanessa has obtained two true-breeding strains of mice,each homozygous for an independently discovered recessive mutation that prevents the formation of hair on the body.The discoverer of one of the mutant strains calls his mutation naked,and the other researcher calls her strain hairless.To determine whether the two mutations are simply alleles for the same gene,Vanessa crosses naked and hairless mice with each other.All the offspring are phenotypically wild type.After intercrossing these F₁ mice,however,Vanessa observes 115 wild-type mice and 85 mutant mice in the F₂. a)What is the most likely explanation for the segregation of wild-type mice and mutant mice in the F₂? Are the naked and hairless mutations alleles for the same gene? b)Using symbols of your own choosing,indicate the genotypes of the parents,the F₁,and each of the phenotypic classes of the F₂ progeny.Describe any gene interactions in this set of crosses.

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Question 6

Several pairs of light brown hamsters with identical genotypes were mated.Altogether,the F₁ was comprised of 143 individuals: 62 light brown,41 brown,38 beige (very,very light brown),1 dark brown,and 1 white.What mode of inheritance of the phenotype "fur color" could most easily explain these results?

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Question 7

You generated a plant that is heterozygous for three quantitative trait loci (QTL).In the heterozygous state,each locus has one allele that contributes one dose of trait (pigment)and another allele that does not contribute a dose to the trait;genotype: R₁/r₁;R₂/r₂;R₃/r₃.If you testcross this plant (by r₁/r₁;r₂/r₂;r₃/r₃ all "0-dose" alleles)what distribution of pigment doses would be observed in the progeny?

Accepted Answer

Each locus segregates independently, and for each, there's a 1/2 chance of contributing a dose of pigment. The combinations for 0, 1, 2, or 3 doses follow a binomial distribution, leading to 1/8 with three doses, 3/8 with two doses, 3/8 with one dose, and 1/8 with zero doses.

Question 8

In a perfectly controlled laboratory environment,a pure-breeding fish with a 23-mm tail was crossed to a pure-breeding fish with a 15-mm tail.In the F₁,all individuals had tails of an intermediate length: 19 mm.If tail length is a typical polygenic trait controlled entirely by the equal and additive effect of two unlinked genes,each with two alleles ("+" and "-"),what phenotypic ratios do you expect to find in the F₂?

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Question 9

Define Mendel's experimental evidence for diploid chromosome content in pea plants.

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Question 10

You just isolated a new strain of mutant mice,and preliminary matings suggest that the new mutant phenotype is not inherited autosomally.Circumstantial evidence seems to indicate that the mutant phenotype may be following either an X-linked dominant or a mitochondrial-type inheritance pattern.
a)What informative crosses would you set up to distinguish between these two possibilities?
b)How would you interpret your results?

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Question 11

In a species of Mexican mollies,fish with ragged fins and nonragged fins were found.When mollies of a true-breeding (i.e.,pure-breeding)ragged strain were crossed with nonragged fish,the F₁ all had ragged fins,and in the F₂,three ragged appeared to one nonragged.Diagram this cross,letting R = ragged and r = nonragged,and give parental phenotypes,genotypes,and germ cells,as well as F₂ genotypes and phenotypes.

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Question 12

Suppose red-striped laughing frogs are diploid and have 32 chromosomes in somatic cells.Answer the following questions as they pertain to these vanishingly rare but beautiful creatures.
a)How many pairs of homologous chromosomes does a red-striped laughing frog have in its somatic cells?
b)How many chromosomes are there in a haploid set?
c)How many chromosomes are there in a mature sperm cell?
d)How many chromosomes are there in a somatic cell just after mitosis?
e)How many double-stranded DNA molecules are there in a somatic cell as mitosis is about to start?
f)How many chromosomes are there in a cell prior to DNA replication?

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Question 13

An arginine-requiring strain of Neurospora is crossed to a wild-type (prototrophic)strain.
a)In the first cross,half of the progeny are arginine-requiring and half are wild type.What does this tell you about the genetic basis of the arginine-requiring mutant?
b)In the second,the progeny are 83 arginine-requiring and 13 wild type.The germination percentage of ascospores is 95/100%.Explain these results simply,and tell briefly how you would confirm your explanation.

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Question 14

The pedigree below shows the inheritance of a rare muscle condition in bats.What inheritance model best explains the peculiar pattern?

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Question 15

Two haploid yeast cells,one wild type and one having a mutation blocking the synthesis of adenine,were mated to produce a diploid zygote.Through asexual reproduction (mitosis),this zygote gave rise to hundreds of identical cells,and all were wild type in phenotype.These (diploid)cells were then induced to undergo meiosis,and the progeny (a random sample of haploid meiotic products)consisted of 214 cells able to grow without adenine and 203 unable to grow without adenine.
a)Diagram the cross,picturing the chromosomes of the parents,the zygote,metaphase I,and the meiotic products.
b)How many genes are involved?
c)What are the dominance relationships of the alleles of the gene or genes?

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Quiz 3: Independent Assortment of Genes

If stem length in a certain species of crops was solely determined by polygenic inheritance,how many different genes would be required in this system to explain the existence of 15 different stem lengths ranging from 15 to 29 cm?

Define Mendel's experimental evidence for diploid chromosome content in pea plants.

The pedigree below shows the inheritance of a rare muscle condition in bats.What inheritance model best explains the peculiar pattern?