Use the pedigree to answer the question. What is Sandra’s genotype for this trait? A. She must be AA. B. She must be Aa. C. She can be either aa or AA. D. She can either be AA or Aa.

BPA and Abnormal Meiosis In 1998, researchers at Case Western University were studying meiosis in mouse oocytes (germ cells) when they saw an unexpected and dramatic increase of abnormal events (FIGURE 12.6). Improper segregation of chromosomes during meiosis is one of the main causes or human genetic disorders. The spike in abnormal meiosis began right after the mouse facility started washing the animals' plastic cages and water bottles in a new, alkaline detergent. The detergent had damaged the plastic, which as a result was leaching bisphenol A (BPA). BPA is a synthetic chemical that mimics estrogen, the main female sex hormone in animals. Though it has since been banned for use in baby bottles, BPA is still widely used to manufacture other plastic items and epoxies (such as the coating on the inside of metal cans of food). BPA-free plastics are often manufactured with a related compound, bisphenol S (BPS), that has effects similar to BPA. FIGURE 12.6 Abnormalities in meiosis that occurred after exposure to BPA. Top, the most abnormal meiosis events occurred in mice that were housed in damaged plastic caging with damaged plastic bottles. Damaged plastic releases BPA. Bottom, fluorescent micrographs show the chromosomes (red) and spindle (green) in nuclei of mouse germ cells in metaphase I. A Normal metaphase; BD abnormal metaphase. What percentage of mouse oocytes displayed abnormalities of meiosis with no exposure to damaged caging?

Analysis of Autosomal Recessive and Dominant Traits Huntington disease is a rare, fatal disease that usually develops in the fourth or fifth decade of life. It is caused by a single autosomal dominant allele. A phenotypically normal man in his twenties who has a 2-year-old son of his own learns that his father has developed Huntington disease. What is the probability that he himself will develop the disease? What is the chance that his young son will eventually develop the disease?

Figure 7.2 If a mutation occurs so that a fungus is no longer able to produce a minus mating type, will it still be able to reproduce? Figure 7.2 (a) In animals, sexually reproducing adults form haploid gametes from diploid germ cells. (b) Fungi, such as black bread mold (Rhizopus nigricans), have haploid-dominant life cycles. (c) Plants have a life cycle that alternates between a multicellular haploid organism and a multicellular diploid organism. (credit c fern: modification of work by Cory Zanker; credit c gametophyte: modification of work by Vlmastra/Wikimedia Commons)

Figure 1.7 Decide if each of the following is an example of inductive or deductive reasoning. All flying birds and insects have wings. Birds and insects flap their wings as they move through the air. Therefore, wings enable flight. Insects generally survive mild winters better than harsh ones. Therefore, insect pests will become more problematic if global temperatures increase. Chromosomes, the carriers of DNAr separate into daughter cells during cell division. Therefore, each daughter cell will have the same chromosome set as the mother cell. Animals as diverse as humans, insects, and wolves all exhibit social behavior. Therefore, social behavior must have an evolutionary advantage.

Alleles are ___________. a. alternate forms of a gene b. different molecular forms of a chromosome c. always homozygous d. always heterozygous

More Crosses with Pea Plants: The Principle of Independent Assortment In pea plants, long stems are dominant to short stems, purple flowers are dominant to white, and round peas are dominant to wrinkled. Each trait is determined by a single, different gene. A plant that is heterozygous at all three loci is self-crossed, and 2,048 progeny are examined. How many of these plants would you expect to be long stemmed with purple flowers, producing wrinkled peas?

Why do unrelated children with a disorder such as Down syndrome resemble each other more closely than they do their siblings?

If all the nondisjunction events leading to Turner syndrome were paternal in origin, what trisomic condition might be expected to occur at least as frequently?

A duplicated chromosome has ______ chromatids. a. one c. three b. two d. four