A diploid organism whose somatic (nonsex) cells each contain 32 chromosomes produces gametes containing _____ chromosomes.
16 is half of 32.
Which statement correctly describes how cellular DNA content and ploidy levels change during meiosis I and meiosis II?
DNA content is halved in both meiosis I and meiosis II. Ploidy level changes from diploid to haploid in meiosis I, and remains haploid in meiosis II.
Pairing of homologous chromosomes is followed by crossing over, the exchange of genetic material between nonsister chromatids of homologous chromosomes.
A chromosome created when crossing over combines the DNA from two parents into a single chromosome.
At the end of _____ and cytokinesis, haploid cells contain chromosomes that each consist of two sister chromatids.
Which event makes meiosis a reduction division and why?
separation of homologs in meiosis I because it produces 2 haploid (n) daughter cells from a single diploid (2n) parent cell
Somatic cells of roundworms have four chromosomes. How many chromosomes would you find in an ovum from a roundworm?
What is a major difference between mitosis and meiosis I?
Sister chromatids separate in mitosis, and homologues separate in meiosis I.
Crossover, the exchange of segments of homologous chromosomes, takes place during which of the following processes?
How would genetic variation be affected if during meiosis I maternal chromosomes always lined up together on one side of the metaphase plate and paternal chromosomes always lined up on the other side (ignoring the effects of crossing over)?
Gametes would contain either maternal chromosomes only or paternal chromosomes only.
Which of the following creates different combinations of maternal and paternal chromosomes in gametes?
What happens when an individual has an odd number of chromosome sets (e.g., triploidy)?
Their offspring are often sterile
What would be the outcome of meiosis I if none of the homologous chromosomes separate at anaphase?
One daughter cell would be 2n; the other would have no chromosomes.
In 1985 Hassold and Chiu found that the likelihood of miscarriage increased with maternal age. What is the most likely explanation for the relationship between age and miscarriage?
Ova are arrested in meiosis until ovulation. As a result, completion of meiosis in the older woman is more likely to result in aneuploidy or other chromosomal abnormalities.
A black guinea pig crossed with an albino guinea pig produced 12 black offspring. When the albino was crossed with a second black animal, 6 blacks and 6 albinos were obtained. What is the best explanation for this genetic situation?
Albino is recessive; black is dominant
When Mendel crossed yellow-seeded and green-seeded pea plants, all the offspring were yellow seeded. When he took these F1 yellow-seeded plants and crossed them to green-seeded plants, what genotypic ratio is expected?
Which statement most accurately describes the pattern of inheritance for a human disease caused by a dominant allele on the X chromosome (assuming the disease allele is rare)?
Affected fathers have all affected daughters but no affected sons.
For the disease shown in the pedigree, if the disease allele is rare and only one parent is affected (e.g., the couple at the left of generation II), why are the children usually unaffected?
The unaffected parent is usually homozygous for the wild-type.
If two carriers of an autosomal recessive genetic disease have children, what is the chance that their first child will be a carrier?
In humans, blue eyes are inherited as a recessive autosomal trait and color blindness is an X-linked recessive trait. A woman with blue eyes and normal color vision whose father was color blind marries a man who also has normal color vision. He has brown eyes, but his mother had blue eyes. Which of the following do you expect to be true for their sons?
One-fourth of their sons will be color blind and have blue eyes, 1/4 of their sons will be color blind and have brown eyes, 1/4 of their sons will have normal color vision and blue eyes, 1/4 of their sons will have normal color vision and brown eyes.
Whenever the dominant allele of either (or both) gene A or gene B is present, red color is produced. A cross of AaBb × AaBb can be expected to yield how many red offspring out of 16? Assume the genes are not linked.
In humans, ABO blood types refer to glyocproteins in the membranes of red blood cells. There are three alleles for this autosomal gene: IA, IB, and i. The IA allele codes for the A glycoprotein, The IB allele codes for the B glycoprotein, and the i allele doesn't code for any membrane glycoprotein. IA and IB are codominant, and i is recessive to both IA and IB. People with A type blood have the genotypes IAIA or IAi, people with type B blood are IBIB or IBi, people with type AB blood are IAIB, and people with O type blood are ii. If a woman with type AB blood marries a man with type O blood, which of the following blood types could their children possibly have?
A and B
Which event in meiosis accounts for Mendel's principal of segregation?
Separation of homologs at anaphase I
A man and woman are both of normal pigmentation, but both have one parent who is albino (without melanin pigmentation). Albinism is an autosomal (not sex-linked) recessive trait. What is the probability that their first child will be an albino?
Each sperm cell of a horse contains 32 chromosomes. How many chromosomes are in the somatic cells?
In a testcross of an individual that is heterozygous at two loci, the offspring will appear in what ration if the loci are on different chromosomes?
Two different alleles at a given locus act to produce a phenotype that is different from either homozygous phenotype
A researcher examines a cell undergoing meiosis and identifies the nuclei of two daughter cells. Which of the following best represents how the researcher would characterize the cell?
two haploid cells in metaphase II
What is the end result of meiosis and subsequent fertilization of gametes?
an offspring with a chromosome complement unlike that of either parent
What conclusion can be drawn from John Maynard Smith's mathematical model comparing asexual and sexual reproduction?
Asexual reproduction produces more offspring
If a fatal disease were to infect an aspen tree that reproduces by cloning, which of the following effects on the aspen grove would be most likely?
The entire grove would die.
Which of the following statements is the leading hypothesis to explain why many organisms reproduce sexually?
The offspring that result from sexual reproduction are genetically variable, and some of them can fight off diseases more easily than genetically identical offspring.
Which of the following best supports the statement that asexual reproduction is much more efficient than sexual reproduction?
It only takes one parent
Which of the following supports why sexual reproduction is favored in many groups?
Sexually reproducing parents can produce offspring that are unique and lack deleterious alleles.
Which hypothesis explains why many instances of aneuploidy in humans involve chromosome 21?
Aneuploidy tends to be lethal in embryos if it involves chromosomes with a large number of genes.
Which of the following results from the segregation of chromosomes?
Each gamete formed in an organism will have one copy of each gene
Which of the following is NOT a result of disruptive selection?
a change in the mean value for a trait
An important consequence of gene flow in natural populations is that it _____.
tends to reduce genetic differences among populations
Which evolutionary process is least important for conservation biologists concerned about the future direction of evolutionary change in endangered populations?
Which of the following is NOT associated with inbreeding?
Allele frequencies change in a population.
Paleontologists studying fossilized therapsids (a group of mammal-like reptiles that are now extinct) would probably use which of the following species concepts?
A subspecies is _____.
a population that is somewhat distinctive in behavior or appearance from other similar populations, but not different enough to be considered a separate species
Peter and Rosemary Grant observed a small group of the large ground finch that colonized Daphne Major in the Galápagos Islands. Within a few years, the descendants of the colonists had evolved beaks that were much larger than those in the original source population. What factors did the Grants think influenced this evolution?
The original small size of the colonist pool probably resulted in divergence due to founder effects and genetic drift, and natural selection occurred due to larger seeds found on Daphne Major.
Assume a large mountain range is formed, dividing multiple populations of different species. After a vicariant event such as the one described, how would sister taxa appear on a phylogenetic tree?
Species on either side of the mountain would be more closely related to each other than to species on the same side of the mountain.
Which of the following events would best be described as a case of speciation in sympatry?
An individual hermaphroditic plant undergoes meiotic failure, producing diploid pollen and ovules; these self-fertilize, germinate, and grow into several fully fertile tetraploid plants.
What factors contribute to divergence between Hawthorn flies and Apple flies?
The nonnative host species have smaller fruits; natural selection favors flies that breed on the same plant type on which they are born.
Which of the following statements about autopolyploid individuals is correct?
They contain more than two sets of chromosomes.
Imagine two populations descended from a single bird species. After a period of isolation in allopatry, the populations resume inhabiting the same region. Assuming that the only differences between the populations are those listed, which of the following factors would most likely prevent interbreeding?
Population A performs its mating calls in the upper branches of trees; population B performs them on the ground.
Reinforcement of speciation refers to _____.
natural selection favoring mechanisms of prezygotic isolation by selecting against those individuals who mate and form hybrid offspring
Why was mitochondrial DNA so useful in the study of the hybrid zone between Townsend's warbler and hermit warblers?
mtDNA is maternally inherited, so the researchers were able to discover that most hybrids resulted from Townsend's males mating with hermit females.
Cladistic methods of phylogenetics depend on _____.
identifying monophyletic groups based on shared, derived characters
3 ways in which sexual reproduction increases genetic variation
crossing over, independent assortment, randomness of fertilization