A man with type A– blood and a woman with type AB+ blood have a child. Which blood type is impossible for that child to have?

A scientist is working with a new species of insect and is specifically observing the inheritance of two traits: eye color and antennae shape. Eye colors come in red (dominant) and white (recessive), and antennae come in long shapes (dominant) and short shapes (recessive). He performs a dihybrid cross between two insects heterozygous for both traits and observes a ratio of 3:1 (red eyes and long antennae: white eyes short antennae). Which of the following explanations most likely explains the observed ratio?

Passage:

This has seemed a fatal objection to the chromosome view, but it may not be so, as Spillman has argued, so long as it has not yet been shown that all of the dominant characters may be present at the same time. But even admitting this possible way of eluding the objection, the other point raised above concerning the absence of groupings of characters in Mendelian inheritance seems a fatal objection to the chromosome theory, so long as that theory attempts to locate each character in a special chromosome. We shall have occasion to return to this point later.

In recent years most workers in Mendelian inheritance have adopted a new method of formulating their theory. Characters that Mendelize are no longer allelomorphic to each other, but each character has for its pair the absence of that character. This is the presence and absence theory. We can apply this hypothesis to the chromosome theory. For examples, let us assume a new variety or race arises by the loss of a character from that chromosome that has heretofore carried it. The chromosome still remains in existence, since it may carry many other characters besides the one that was lost, and it becomes in the hybrid the mate of the one still retaining that character. If now separation occurs, two classes of germ-cells result, one with and the other without the character; and the observed numerical proportions follow. There is nothing in this assumption that meets with any greater difficulty on the chromosome separation hypothesis than on the earlier view of paired allelomorphs, but it meets with the same difficulties, and as an assumption is neither more nor less in accord with the postulated mechanism.

Excerpt from Morgan, T. H. 1910. Chromosomes and heredity. The American Naturalist, 44:449–496.

Asssume that in a particular studied species of rodents, coat color is an autosomally-inherited trait, with black fur being the dominant phenotype and white fur being the recessive phenotype. In an experiment, a mouse with black fur mates with a mouse with a mouse with white fur. The resultant 26 offspring mice all have grey fur color. Which of the following genetic principles is best demonstrated by this result?

Pea plants have two independently assorted genes that code for seed shape (round or wrinkled) and seed color (yellow or green), respectively. A researcher crosses two pea plants and observes that all F1 offspring have the same phenotype: round shape and yellow seeds. He then performs a test cross with an F1 offspring and observes four different phenotypes in a 1:1:1:1 ratio. Based on this information the researcher concludes the genotypes of the parents.

Which of the following is the correct pairing of recessive alleles?

Consider the pedigree of a recessive trait. Is the trait autosomal or sex-linked?

In peas, the gene for yellow color (C) is dominant to the gene for green color (c). To determine the genotype of an unknown yellow pea, what kind of pea should you cross with it?

Duchenne Muscular Dystrophy is an X-linked recessive genetic disorder, resulting in the loss of the dystrophin protein. In healthy muscle, dystrophin localizes to the sarcolemma and helps anchor the muscle fiber to the basal lamina. The loss of this protein results in progressive muscle weakness, and eventually death.

In the muscle fibers, the effects of the disease can be exacerbated by auto-immune interference. Weakness of the sarcolemma leads to damage and tears in the membrane. The body’s immune system recognizes the damage and attempts to repair it. However, since the damage exists as a chronic condition, leukocytes begin to present the damaged protein fragments as antigens, stimulating a targeted attack on the damaged parts of the muscle fiber. The attack causes inflammation, fibrosis, and necrosis, further weakening the muscle.

Studies have shown that despite the severe pathology of the muscle fibers, the innervation of the muscle is unaffected.

A young girl is diagnosed with Duchenne Muscular Dystrophy, and her mother is pregnant with a baby boy. Which of the following must be true?

Pea plants have two independently assorted genes that code for seed shape (round or wrinkled) and seed color (yellow or green), respectively. A researcher crosses two pea plants and observes that all F1 offspring have the same phenotype: round shape and yellow seeds. He then performs a test cross with an F1 offspring and observes four different phenotypes in a 1:1:1:1 ratio. Based on this information the researcher concludes the genotypes of the parents.

Which of the following is true regarding a recessive allele?

The concept of genomic imprinting is important in human genetics. In genomic imprinting, a certain region of DNA is only expressed by one of the two chromosomes that make up a typical homologous pair. In healthy individuals, genomic imprinting results in the silencing of genes in a certain section of the maternal chromosome 15. The DNA in this part of the chromosome is "turned off" by the addition of methyl groups to the DNA molecule. Healthy people will thus only have expression of this section of chromosome 15 from paternally-derived DNA.

The two classic human diseases that illustrate defects in genomic imprinting are Prader-Willi and Angelman Syndromes. In Prader-Willi Syndrome, the section of paternal chromosome 15 that is usually expressed is disrupted, such as by a chromosomal deletion. In Angelman Syndrome, maternal genes in this section are deleted, while paternal genes are silenced. Prader-Willi Syndrome is thus closely linked to paternal inheritance, while Angelman Syndrome is linked to maternal inheritance.

Figure 1 shows the chromosome 15 homologous pair for a child with Prader-Willi Syndrome. The parental chromosomes are also shown. The genes on the mother’s chromosomes are silenced normally, as represented by the black boxes. At once, there is also a chromosomal deletion on one of the paternal chromosomes. The result is that the child does not have any genes expressed that are normally found on that region of this chromosome.

The parents of the child in Figure 1 decide to have a second child. This child is diagnosed at birth with both cystic fibrosis and Prader-Willi. Cystic fibrosis is an autosomal recessive disorder inherited on chromosome 7. The mother and father are both healthy. What was the probability of the child being born with both Prader-Willi and cystic fibrosis?

Suppose two individuals with the genotypes PPQqRr and ppQqrr mate. What is the probability that their offspring will display the genotype PpQQRr?