Mastering 28 – Flashcards
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Which of the following would be true of a plant heterozygous for a single gene controlling flower color? (Assume complete dominance).
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If crossed with another heterozygous plant, the majority of progeny will have the dominant flower color.
There will be roughly three times as many plants with the dominant flower color as plants with the recessive flower color.
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True or false?
The 3:1 phenotypic ratio observed among progeny of an F1 X F1 cross requires random union of gametes.
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True
The 1:2:1 genotypic ratio represents relative probabilities of gamete combinations based on the assumption that gamete union is random.
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Of the methods listed below, which would be the best way to determine which of two alleles of a gene is dominant to the other?
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Observe the relevant phenotype in the progeny that result from a cross between individuals from two different pure-breeding lines.
All progeny will be heterozygous for the trait in question and will display the phenotype that corresponds with the dominant allele.
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True or false?
The law of independent assortment states that one gene in a pair is always dominant to the other.
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False
The law of independent assortment states that during gamete formation, segregating pairs of unit factors assort independently of each other; the law says nothing about dominance.
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If a yellow pea plant with round seeds that has the genotype GgWw is crossed to itself, what proportion of the offspring will be green with round seeds?
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3/16
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The following phenotypic ratios are determined for a trihybrid cross in which the gametes assort independently:
A 1 : A 2 = ¼ : ¾
B 1 : B 2 = ¼ : ¾
C 1 : C 2 = ¾ : ¼
What is the probability that the F2 offspring will have the phenotype A 1 B 1 C 1?
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3/64
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Independent assortment explains _______.
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why a collection of meiotic products that includes gametes of genotype Ab will also include gametes of genotype AB in roughly the same proportion
Because alignment of the chromosomes is random, the alignment that produces Ab is just as likely as the alignment that produces AB. Therefore, the two genotypes should both occur with equal frequency.
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True or false?
Independent assortment occurs only in cells that are heterozygous for two genes (AaBb) and not in cells that are completely homozygous (AABB or aabb).
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False
Even though there would be no genotypic differences in the products of such meioses, random alignment of chromosomes would still have occurred.
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Which of the following genotypes represents a gamete produced by a failure to segregate during meiosis in a cell of genotype AaBbCC?
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AaBC
This gamete contains two copies of gene "A". Proper segregation would have separated A from a and allowed only one copy per gamete.
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You would like to know whether the progeny of a pair of mated fruit flies are distributed among the resulting four phenotypic classes in a 1:1:1:1 ratio. You perform a chi-square test and obtain a p value of 0.04. Assuming you have done the test correctly, select the best interpretation of this result.
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The differences between the observed and expected counts are too large to be attributed to chance.
It is on this basis (p< 0.05) that the decision to reject the hypothesis of a 1:1:1:1 ratio is made.
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True or False?
The larger the number of total individual counts in a chi-square test, the higher the degrees of freedom (df).
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False
df increases with increasing n (number of categories), but not necessarily with increasing number of subjects.
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The expected ratio of phenotypes among the progeny of a test cross is 1:1:1:1. Out of 200 total resulting progeny, 48 occur in one of the four phenotypic classes. Given this information, which of the following must also be true?
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The value of observed - expected for this cell = -2.
With a total of 200, the expected number in each cell when the predicted ratio is 1:1:1:1 = 50. The observed number is 48.
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Crosses in which F1 plants heterozygous for a given allele are crossed to generate a 3:1 phenotypic ratio in the F2 generation are known as
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Monohybrid cross
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In peas, the round allele is dominant over the wrinkled allele. If a plant with round peas is crossed to a plant with wrinkled peas, all of the resulting plants have round peas. What is the genotype of the parents in this cross?
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RR x rr
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In peas, the yellow allele is dominant over the green allele. If a plant with yellow peas is crossed to a plant with green peas, the resulting plants are 50% yellow and 50% green. What is the genotype of the parents in this cross?
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Yy x yy
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Assuming independent assortment, what phenotypic ratio would you expect to see if an individual with the genotype RrGg is self-crossed?
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9:3:3:1
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In peas, axial (A) flower position is dominant to terminal (a), tall (L) is dominant to short (l), and yellow (Y) is dominant to green (y). If a plant that is heterozygous for all three traits is allowed to self-fertilize, how many of the offspring would be dominant for all three traits?
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27/64
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What phenotypic ratio would you expect as a result of a test cross between a dihybrid organism and one that is homozygous recessive for alleles at two independent loci?
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1:1:1:1
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Mendel's law of segregation predicts the following specific phenotypic ratios among the F1 and F2 progeny from crosses between two pure-breeding parents for a single trait (e.g., yellow vs. green peas).
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F1 1:0 F2 3:1
A monohybrid cross for a dichotomous trait always yields a single phenotype (the dominant trait) in the F1 and a 3:1 phenotype ratio (3 dominant : 1 recessive) in the F2.
