Exam 19: Sexual Reproduction and the Power of Genetics

For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below.Not all words or phrases will be used; each word or phrase may be used more than once. allele genotype monohybrid chromosome heterozygous pedigree dependent homozygous phenotype dihybrid independent segregation Gregor Mendel studied pea plants and developed some very important ideas about how genes are inherited.These studies used plant strains that were true-breeding and always produced progeny that had the same __________ as the parent.These strains were true breeding because they were __________ for the gene important for a specific trait.In other words, for these true-breeding strains, both chromosomes in the diploid pea plant carried the same __________ of the gene.Mendel started out examining the inheritance of a single trait at a time, and then moved on to examining two traits at once in a __________ cross.His studies examining the inheritance of two traits in one cross allowed him to discover what is now known as Mendel's law of __________ assortment.Geneticists can study the inheritance of specific traits in humans by analyzing a __________, which shows the phenotypes of different family members over several generations for a particular trait.

Imagine meiosis in a diploid organism that only has a single chromosome.Like most diploid organisms, it received one copy of this chromosome from each of its parents and the two homologs are genetically distinct.If only a single homologous recombination event occurs during meiosis, which of the following choices below correctly describes the four gametes formed?

During recombination

Do you AGREE or DISAGREE with the following statement? Explain your answer. A trait that is found at a low frequency in the population must be a recessive trait.

Sickle-cell anemia is caused by a mutant allele of a hemoglobin gene.Individuals with two mutant alleles have sickle-cell anemia.Individuals homozygous and heterozygous for the mutant gene are more resistant to malaria than those with two wild-type alleles.Given this information, would you classify this mutant allele as behaving as a dominant, recessive, or codominant allele?

Figure 19-24 diagrams one of Mendel's experiments using the round and wrinkled seed traits. Figure 19-24 If you crossed the round-seeded plants obtained in the F₁ generation with a true-breeding strain of wrinkle-seeded plants, how many round-seeded plants would you expect to obtain in the next generation?

Organisms that reproduce sexually

A single nondisjunction event during meiosis

For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below.Not all words or phrases will be used; each word or phrase can be used only once. allele germ pollen bivalent meiosis somatic eggs mitosis sperm gametes pedigree zygote To reproduce sexually, an organism must create haploid __________ cells, or __________, from diploid cells via a specialized nuclear division called __________.During mating, the father's haploid cells, called __________ in animals, fuse with the mother's haploid cells, called __________.Cell fusion produces a diploid cell called a __________, which undergoes many rounds of cell division to create the entire body of the new individual.The cells produced from the initial fusion event include __________ cells that form most of the tissues of the body as well as the __________-line cells that give rise to the next generation of progeny.

Loss-of-function mutations

Your friend has obtained some pea seeds from the Abbey of St.Thomas in Brno, where Gregor Mendel worked.He is very excited because not only did he obtain some yellow and green pea seeds from true-breeding plants (like the ones used in Mendel's famous experiment), he was also able to obtain some purple pea seeds from a true-breeding plant.First, your friend takes the true-breeding yellow and green pea seeds, repeats the cross that Gregor Mendel did, and obtains the same results: he sees 100% yellow-seeded pea plants in the F₁ generation, and 75% yellow-seeded pea plants and 25% green-seeded pea plants in the F₂ generation.His results are illustrated in Figure 19-30A.Your friend then decides to set up two more crosses.For cross #2, he crosses the true-breeding purple-seeded pea plants to the true-breeding yellow-seeded pea plants.The results from this cross are shown in Figure 19-30B.Next, for cross #3, he crosses the true-breeding purple-seeded pea plants to the true-breeding green-seeded pea plants.These results are shown in Figure 19-30C. Figure 19-30 Given these results, if you were to take the purple-seeded pea plants produced in the F₁ generation in cross #2 and cross them to the purple-seeded pea plants produced in the F₁ generation of cross #3, what do you expect that the phenotype of the progeny would look like? Explain your answer.

Which of the following statements about meiosis is TRUE?

You examine a worm that has two genders: males that produce sperm and hermaphrodites that produce both sperm and eggs.The diploid adult has four homologous pairs of chromosomes that undergo very little recombination.Given a choice, the hermaphrodites prefer to mate with males, but just to annoy the worm, you pluck a hermaphrodite out of the wild and fertilize its eggs with its own sperm.Assuming that all the resulting offspring are viable, what fraction do you expect to be genetically identical to the parent worm? Assume that each chromosome in the original hermaphrodite is genetically distinct from its homolog.

Which of the following statements about conditional alleles is FALSE?

Which of the following statements is TRUE?

Which of the following does not describe a situation of asexual reproduction?

Which of the following statements most correctly describes meiosis?

Any two human beings typically have an estimated 0.1% difference in their nucleotide sequences, which is equivalent to about 3 million nucleotide differences.These differences are the basis of the SNPs used to construct genetic linkage maps.Some of these SNPs actually lie in the region of the DNA that codes for the protein, yet they have no effect on the phenotype of individuals carrying the SNP on both homologous chromosomes.Explain how some SNPs can lie within the portion of the DNA that codes for the protein and yet have no discernible effect on the protein's activity.

With respect to gene E on the chromosome drawn in Figure 19-14, which gene is least likely to behave according to Mendel's law of independent assortment? Explain your answer. Figure 19-14

The single-nucleotide polymorphisms found in the human population