Exam 3: Basic Principles of Heredity

In peas, tall (T) is dominant to short (t). A homozygous tall plant is crossed with a short plant. The F₁ plants are self-fertilized to produce the F₂. Both tall and short plants appear in the F₂. If the short F₂ plants are self-fertilized, what types of offspring and proportions will be produced?

What important genetics concept is being shown in the diagram?

Two gene loci, A and B, assort independently, and alleles A and B are dominant over alleles a and b. -What is the probability of producing an AB gamete from an AABb individual?

While doing fieldwork in Madagascar, you discover a new dragonfly species that has either red (R) or clear (r) wings. Initial crosses indicate that R is dominant to r. You perform three crosses using three different sets of red-winged parents with unknown genotype and observe the following data: Cross Phenotypes 1 72 red-winged, 24 clear-winged 2 12 red-winged 3 96 red-winged Which cross is likely to have at least one parent with the genotype RR?

In a cross between pure-breeding tall plants with pure-breeding short plants performed by Mendel, all of the F₁ are tall. When these plants are allowed to fertilize themselves, the F₂ plants occur in a ratio of 3 tall to 1 short. Which of the following is NOT a valid conclusion from these results?

Let us assume that hairy toes (hh) and brittle ear wax (ww) are both recessive traits in humans. In families of three children where both parents are heterozygotes at both loci (they have smooth toes and sticky ear wax) what is the probability that the family will consist of one hairy-toed, brittle ear-waxed boy and two smooth-toed, sticky ear-waxed girls?

In dogs, black coat color (B) is dominant over brown (b), and solid coat color (S) is dominant over white spotted coat (s). A cross between a black, solid female and a black, solid male produces only puppies with black, solid coats. This same female was then mated with a brown, spotted male. -Have of the offspring from this cross were black and solid, and half of the offspring were black and spotted. Which of the following could be the genotype of the black, solid male?

In a cross between AABbCcDD and AaBbccdd, what proportion of the offspring would be expected to be A_B_C_D_? (A_ means AA or Aa.)

Two pea plants with purple flowers are crossed. Among the offspring, 63 have purple flowers, and 17 have white flowers. With a chi-square test, compare the observed numbers with a 3:1 ratio and determine if the difference between observed and expected could be a result of chance.

Freckles are caused by a dominant allele. A man has freckles but one of his parents does not have freckles. The man has fathered a child with a woman that does not have freckles. What is the probability that their child has freckles?

The following cross produced 125 progeny: aaBbCcDd × AaBbccDD. Assume all the genes assort independently and that the uppercase letters represent dominant alleles. a. How many offspring are expected to express the phenotype ABCD? b. How many offspring are expected to have the genotype aaBBccDd? c. How many offspring are expected to have the genotype AaBbCcDd?

Sex in mammals is determined by the X and Y sex chromosomes: Males are XY and females are XX. How do you explain the 50-50 sex ratio in mammalian progeny?

If two heterozygous Aa plants are crossed with each other, what will be the genotypic ratio found in the offspring?

If an AaBbccDd individual is crossed to an AaBbCcDDindividual, what is the probability that the first offspring will be of AabbccDd genotype?

Genes come in different versions called:

Which statement(s) about probabilities is/are TRUE? (Select all that apply.)

Two gene loci, A and B, assort independently, and alleles A and B are dominant over alleles a and b. -What is the probability of producing an AB gamete from an AaBb individual?

Round seeds (R) are dominant to wrinkled seeds (r), and yellow seeds (Y) are dominant to green seeds (y). A plant of unknown genotype is testcrossed to a true-breeding plant with wrinkled and green seeds. The offspring produced were 53 round and yellow, 49 round and green, 44 wrinkled and yellow, and 51 wrinkled and green. What is the likely genotype of the parent in question?

In dogs, black coat color (B) is dominant over brown (b), and solid coat color (S) is dominant over white spotted coat (s). A cross between a black, solid female and a black, solid male produces only puppies with black, solid coats. This same female was then mated with a brown, spotted male. -Half of the offspring from this cross were black and solid, and half of the offspring were black and spotted. What is the genotype of the female?

In a plant species, you notice that purple and yellow leaf colors, as well as hairy and smooth stems, segregate. In this species, yellow (P) is dominant to purple (p), and hairy (S) is dominant to smooth (s). You cross a plant with purple leaves and hairy stems to a plant with yellow leaves and hairy stems and generate the following progeny: Progeny Class Phenotypes 1 68 yellow leaves, hairy stems 2 66 purple leaves, hairy stems 3 22 purple leaves, smooth stems 4 25 yellow leaves, smooth stems Total: 181 a. Indicate the most likely genotypes for each parent. b. Propose a hypothesis to explain the progeny results. Based on this hypothesis, what ratios are expected for each of the four classes of progeny? c. Using the chi-square method, test your hypothesis and indicate whether you accept or reject it.