Chapter 3 Mastering Genetics

The 9:3:3:1 ratio exhibited in the F2 generation of a dihybrid cross is a genotypic ratio.

false

The larger the number of total individual counts in a chi-square test, the higher the degrees of freedom (df).

False. df increases with increasing n (number of categories), but not necessarily with increasing number of subjects.

What is the probability of a family with six children having three boys and three girls?

20/64

If the first three F2 offspring grown from the cross described above are round, what is the probability that the next F2 offspring will be wrinkled?

25%. The proportion of rr is ¼, so the next offspring has a 25% chance of being wrinkled.

When a F1 plant (heterozygote--Gg) undergoes meiosis, what gamete types will it produce, and in what proportions?

1/2 G and 1/2 g

Choose the offspring phenotypes you would expect from the following cross: R 1 R 2 × R 2 R 2 R1R1 red R1R2 pink R2R2 white

1/2 pink, 1/2 white The genotypic ratio for this cross is 1/2 R 1 R2 and 1/2 R 2 R 2, making the phenotypic ratio 1/2 pink and 1/2 white.

Incomplete dominance is shown in the flower color of snapdragons, as shown in this figure. Choose the offspring phenotypes you would expect from the following cross: R 1 R 1 × R 1 R 2 R1R1 red R1R2 pink R2R2 white

1/2 red, 1/2 pink The genotypic ratio for this cross is 1/2 R 1 R 1 and 1/2 R 1 R 2, making the phenotypic ratio 1/2 red and 1/2 pink.

If three differently colored dice are rolled at the same time, what is the probability that a 6 will be the outcome on each one?

1/216 because, 1/6 x 1/6 x 1/6

Choose the offspring phenotypes you would expect from the following cross: R 1 R 2 × R 1 R 2 R1R1 red R1R2 pink R2R2 white

1/4 red, 1/2 pink, 1/4 white The genotypic ratio for this cross is 1/4 R 1 R 1, 1/2 R 1 R 2, and 1/4 R 2 R 2, making the phenotypic ratio 1/4 red, 1/2 pink, and 1/4 white.

A pea plant is heterozygous for two genes; one controlling height, one controlling color. The genotype is written PpTt. Based on the Law of Independent Assortment, approximately what proportion of the pollen produced by this plant should have the genotype PT?

1/4. There are four different possible genotypes. Independent Assortment assumes that all are equally likely. Therefore, each of the four should occur with roughly equal frequency (1/4).

Round (R) seed shape is dominant to wrinkled (r) seed shape in pea plants. If an RR plant is crossed with an rr plant, what is the frequency of phenotypes in the F2 generation?

3 round seeds, 1 wrinkled seed. The F1 generation would have the genotype Rr, so crossing two heterozygotes would result in 3 plants with round seeds and 1 plant with wrinkled seeds.

What is the expected phenotypic ratio of a cross between a disc-shaped squash that is heterozygous at both loci and a long squash?

4⁄16 disc, 8⁄16 sphere, 4⁄16 long The genotypic ratio for this cross is 4⁄16 AB, 4⁄16 Ab, 4⁄16 aB, and 4⁄16 ab, making the phenotypic ratio 4⁄16 disc, 8⁄16 sphere, 4⁄16 long.

Mendel studied pea plants dihybrid for seed shape (round versus wrinkled) and seed color (yellow versus green). Recall that -the round allele (R) is dominant to the wrinkled allele (r) and -the yellow allele (Y) is dominant to the green allele (y). The table below shows the F1 progeny that result from selfing four different parent pea plants. Use the phenotypes of the F1 progeny to deduce the genotype and phenotype of each parent plant. Complete the table by dragging the correct label to the appropriate location. Labels can be used once, more than once, or not at all.

Chapter 3, #6, part A

A plant grown from a [round, yellow] seed is crossed with a plant grown from a [wrinkled, yellow] seed. This cross produces four progeny types in the F1: [round, yellow], [wrinkled, yellow], [round, green], and [wrinkled, green]. Use this information to deduce the genotypes of the parent plants.

Chapter 3, #6, part B

For the cross in Part B, predict the frequencies of each of the phenotypes in the F1 progeny, and determine the genotype(s) present in each phenotypic class.

Chapter 3, #6, part C

Pedigree Analysis

Chapter 3, #9

Mendel's Law of Segregation

Allele pairs segregate equally into gametes during meiosis. A gamete will have only one allele of any given gene and that the probability of a gamete having one allele or the other is equal.

Which of the following would be true of a plant heterozygous for a single gene controlling flower color? (assume complete dominance).

If crossed with another heterozygous plant, the majority of progeny will have the dominant flower color.

Which of the following statements about autosomal recessive traits is true?

If neither parent expresses the trait, but the offspring does, both parents must be heterozygous for the trait. For an autosomal recessive trait to be expressed, the individual must be homozygous for the recessive allele. The only way (excluding new mutations) for homozygous recessive offspring to be produced from parents who do not express the trait is if both parents are heterozygous for the trait.

Of the methods listed below, which would be the best way to determine which of the two alleles of a gene is dominant to the other?

Observe the relevant phenotype in the progeny that result from a cross between individuals from two different pure-breeding lines.

Which term describes the individual in a pedigree whose phenotype was first brought to the attention of a medical researcher?

Proband The proband is the affected individual who is first brought to the attention of a medical researcher; usually the pedigree is constructed around this individual.

What is the most likely mode of transmission for a trait that is not expressed in parents but is expressed by one half of the sons?

Rare X-linked recessive This trait is X-linked, and since only half the sons are affected, it is a recessive trait and the mother must have been heterozygous.

What are Punnett squares used for?

Representing the types and frequencies of gametes and progeny in experimental crosses. The probability of two independent events occurring simultaneously is the product of their individual probabilities

The 1:2:1 genotypic ratio

Represents relative probabilities of gamete combinations based on the assumption that gamete union is random

True-Breed

The alleles are homozygous.

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.

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.

Which of the following statements about an individual with the Bombay phenotype is correct?

The individual lacks the enzyme required to produce the H substance. Individuals with the Bombay phenotype are homozygous hh and do not make the enzyme required to produce the H substance. Thus, they cannot modify the H substance to produce the antigens on which type A and B blood phenotypes are based.

Which of the following phenomena is a consequence of Independent Assortment?

The phenotypic ratio among phenotypes produced from an F1 xF1 dihybrid cross is 9:3:3:1 The 9:3:3:1 ratio requires that the four gamete classes produced occur with equal frequency. This requires independent assortment.

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?

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.

The 3:1 phenotypic ratio observed among progeny of an F1 X F1 cross requires random union of gametes.

True

In an individual that is heterozygous for a particular trait, the recessive allele is not expressed.

True. Only the dominant allele is expressed in an individual that is heterozygous for a particular trait.

In a cross between two strains that are true breeding for purple and white flowers, the F2 phenotypic ratio would be ¼ purple, ¼ white, and ½ lavender if the flower color phenotype exhibits incomplete dominance.

True. The heterozygous offspring exhibit a phenotype that is intermediate between the parents.

A couple has two boys and is expecting a third child. The probability that the third child will be a boy is 1/2.

True; the probability of having a girl is also 1/2. The sex of the previous children does not influence the sex of the third child.

Choose the offspring phenotypes you would expect from the following cross: R 1 R 1 × R 2 R 2 R1R1 red R1R2 pink R2R2 white

all pink. The genotypic ratio for this cross is all R 1 R 2, making the phenotypic ratio all pink.