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GENETICS: TYPICAL TEST QUESTIONS [Look at the underlined words and select the word that correctly completes each statement by circling it.] 1. In mitosis/meiosis, the haploid / diploid parent cell undergoes a process in which one /two/ four cells are produced that are smaller but identical to the parent cell. In mitosis/meiosis, the haploid /diploid parent cell undergoes a process in which one /two / four cells are produced that are not identical to the parent cell. Fill in the blanks: 2. Humans have ______23 Pairs of_____ chromosomes, __ 23_(half)__ of which are provided by the female and _____23_(half)_ of which are provided by the male. Thus we get _two_ copies of every gene, which is why every gene has ___two_____ alleles. 3. In humans, chromosome pair # 23 are the sex chromosomes because it is the pair that determines weather a child will be male or female. In males, the chromosome pair is identified as: ___Xy________; in females, as _____XX_____. Matching. Match the phrase in the column on the left with the correct word(s) in the column on the right. Write the letter to the left on the number on this paper. 4._ I Outward appearance on inherited traits A. incomplete dominance 5.__E B. meiosis Variations of a gene that can be passed on 6.__L Both alleles phenotypes are seen individually in the organism C. gene 7.__F The allele whose phenotype is expressed in heterozygous individuals D. trait 8.__N When a person has two different alleles controlling a trait E. allele 9.__M Pair of identical alleles F. dominant 10._O The first generation produced in a breeding experiment G. recessive 11._H H. genotype The genetic makeup of an individual 12._G The form of a trait that is not seen in heterozygous individuals I. Phenotype 13.__J The passing of traits from parents to the offspring J. heredity 14._A Both alleles blend together to create a phenotype K. genetics 15._K The study of how genotypes affect phenotypes in organisms L. codominance M. homozygous N. heterozygous O. F1 Generation MULTIPLE CHOICE. Choose the single, best answer to complete each question and circle it. 16. In a Punnett square a capital letter (like “T” or “E”) stands for which type of allele? a. dominant c. recessive b. heterozygous d. sex-linked 17. For every trait, there is at least one type of gene and ______ allele(s) that control that trait. a. one c. four b. two d. as many as eight 18. The combination Tt represents a ______ genotype. a. heterozygous c. b. homozygous d. codominant sex linked 19. Explain how genes are passed down from each parent to the off spring. Think back to your skittle lab. Ans. Both Parents have 23 pairs of chromosomes. Those chromosomes carry our genes and those genes determine what traits we outwardly show (phenotypes). Each chromosome pair has the same set of genes but the version of each gene may differ (alleles). We receive one of each of Mom’s pairs of chromosomes, and one of each of our Dad’s 23 pairs of chromosomes. (Look back at your notes when we drew out mitosis and meiosis with colored pencils.) Some of the mom’s body cells go through Meiosis to create eggs that contain half a set of 23 chromosomes and the dad’s body cells go through meiosis to create sperm containing only ½ a set of chromosomes. Therefore, when one of Mom’s eggs joins with one of Dad’s sperm, we have a new human with its own unique set of 23 chromosome pairs. 20. In the, “Bunny Evolution Lab”, why did the frequency of the dominant allele (F) increase even though the amount of F alleles in the population remained the same after each generation. Ans. The lab began with 50 F alleles (black beans) and 50 f alleles (white beans). Rabbits were born when mother nature put two random alleles together. (She pulled two beans from the bag. This represents two possible alleles that could end up together after two rabbits from the current population mated. Each rabbit provides one allele from his sperm or egg.) Bunnies who were FF, or Ff had fur and bunnies who were ff did not have fur. Furless bunnies died during the winters and thus the frequency of the f allele went down because the f alleles from the ff bunnies were no longer able to be passed on the following spring during mating season (dead bunnies can’t pass on genes). As the proportion of f alleles grew smaller the proportion of F alleles available during mating season increased. 21. Brown hair and long eyelashes are examples of: a. alleles. b. phenotypes c. genotypes. d. genes. 22. According to the law of Incomplete Dominance, if red carnations (RR) are crossed with white carnations (WW), the offspring will be: a. red. c. pink b. white. d. red and white SHORT ANSWER. Complete sentences are not required. PTC tasting (T) is dominant over not tasting. Dimples (D) are dominant over no dimples. Show Punnett in the blank space provided below each question. 23. Make a Punnett Square to show all possible combinations of offspring that could result from a parent who is homozygous dominant for PTC tasting and a parent who is homozygous recessive for the same trait. a. What is the written (not abbreviated) genotype of the offspring? Tt b. List all possible phenotypes of the F1 generation. PTC tasting TT x tt t t T Tt Tt T Tt Tt 24. Simple Dominance: Fill in the Punnett Square to show all possible combinations of offspring that could result from two parents who are both heterozygous (hybrid) for dimples. What percent of the offspring will have the same genotype as the parents? a. What percent of the offspring will have the same phenotype as the parents? 75% b. What fraction of the offspring will be homozygous recessive? 25% c. What fraction of the offspring will have the ability to pass on the recessive trait? 75% D d D DD Dd d Dd dd 25. Incomplete Dominance: Black color (BB) is incompletely dominant over white (WW) in pig fur colors, resulting in the color gray. Fill in the Punnett Square to show all possible combinations of offspring that could result from two parents who are both gray. a. List all possible genotypes and phenotypes in the resulting offspring. Geno (BB, BW, WW) Pheno(Black, Gray, White) b. What percent of the offspring will have the same phenotype as the parents? 50% c. What fraction will be black? 25% B W B BB BW W Bw WW 26. Codominance: Explain the difference between incomplete dominance and codominance. Give an example. Codominance: Two alleles such as Red – R and White – W are expressed independently in the phenotype of an individual that is heterozygous for that trait. If a flower that is RW – you would see red and white dots for example. Incomplete Dominance yields a phenotype that is a mix of the two individual alleles. A flower that is RW would have a pink phenotype in this case. 27. Two-Factor Cross: In pea plants, the “tall” allele is dominant over the short one, and yellow is dominant over green. Cross two plants that are hybrid for both traits. Show the Punnett Below (Review the Gene Interactions Hwk to find the correct punnett square and answers) a. List all possible genotypes and phenotypes. b. What is the ratio of resulting phenotypes? 9 Tall Yellow: 3 Tall green: 3 Short Yellow: 1 short green c. What fraction of the offspring will be homozygous recessive for both traits? 1/16 d. What fraction of the offspring will be tall and yellow? 9/1 RrYy RY Ry RY Ry rY ry RRYY RRYy RrYY RrYy RRYy RRyy RrYy Rryy RrYy F generation 2 rY RrYY RrYy rrYY ry RrYy Rryy rrYy rrYy Figure 3. If the genes f or two traits are not linked, then they will undergo independent assortment. This results in new combinations of the traits. rryy 28. Sex-Linked Traits: Hemophilia is a sex-linked trait. Show a cross between a woman who is a carrier and a man who has hemophilia. (Save this for test review day if you don’t know how to d this punnett.) a. What percent of the female offspring will be carriers of the disease? 50% b. What percent of the female offspring will have hemophilia? 50% c. What percent of the male offspring will have hemophilia? 50% h X y XH XH Xh XH y Xh Xh Xh Xh y Emphasize that a carrier is a person who is heterozygous and thus does not HAVE the disease, but they are CARRYING the disease as a recessive allele that can be passed down to their kids. A person who has the disease is not called a carrier. A male either has the disease or does not have the disease because the disease is linked onto the X chromosome and males only have one X chromosome. 29. Polygenetic Inheritance: Tail length in cats is determined by more than one gene. Show all possible offspring resulting from the mating of an individual with an average length tail (AAbb) and an individual with a longer-thanaverage tail (aaBb). No tail = AABB Short tail = AaBB or AABb Average tail = AaBb or AAbb or aaBB Longer-than-average tail = Aabb or aaBb Very long tail = aabb a. What fraction of the offspring will have tails that are shorter than their parents’ tails? -0% b. What fraction of the offspring will have the same genotype as the parent with the longerthan-average length tail? 0% c. What fraction of the offspring will have the same phenotype as the parent with the longerthan average length tail? 1/2 P: AAbb x aaBb Ab Ab Ab Ab aB AaBb ab Aabb aB AaBb ab Aabb 30. DNA is composed of nitrogenous bases – adenine, thymine, guanine and cytosine – phosphate and sugar (deoxyribose). It forms strands that link together in a predictable manner, forming a twisted ladder shape called a double helix. If one side of the DNA strand is AGGTTAC, what is the nitrogenous base order for the complementary strand? S-A T-S P P S-G C-S P P S-G C-S P P S-T A-S P P S-T A-S P P S-A T-S P P S-C G-S 31. Why is it necessary for the nitrogenous bases to break apart during DNA replication? The nitrogenous bases/nucleic acids (ATCG) must break apart so the cell can use each strand as a template or guide indicating what new bases should be added to make two complete double helixes. See number 33 for further explanation. 32. As discussed in the film “What Darwin Never Saw”, what are the most important factors that cause evolution? Explain how these factors contribute to the evolution of a species. A change in the environment occurs, creating a natural selection event, that renders some traits more successful than others. (Example – Winter makes Fur on bunnies preferable to bunnies with no fur.) Thus, successful traits are passed on to the next generation at a higher frequency than the others. This changes the genetic makeup of the species. (As the no fur alleles were purged from the bunny population as those bunnies homozygous for ff died each winter, less and less f alleles were present in the future generations. This changed the population of bunnies from a mix of those with no fur and fur to a species with only fur.) 33. Describe and draw a diagram of the structure of DNA DNA Structure S-A T-S P P S-G C-S P P S-G C-S P P S-T A-S P P S-T A-S P P S-A T-S P P S-C G-S Description of the Structure. The backbone of both sides of the helix are composed of sugars (S) and phosphates (P). Attached to each sugar is a nucleic acid (A-Adenine, T- thymine, C-cytosine, or G-Guanine). A always pairs with a T and C always pairs with a G. The DNA forms into the shape of a double helix. The nucleic acids (ATCG) on each side of the helix are stuck together via hydrogen bonds. 34. Explain how DNA replicates. Include a diagram. 1. The two sides of the helix separate as a molecular machine moves through and breaks the hydrogen bonds between them. S-A T-S P P S-G C-S P P S-G C-S S-A P S-G P S-G T-S P C-S P C-S 2. Now each of the separated strands can act as a template or guide that the cell can use to put in the complimentary bases for the missing strand. S-A P S-G P S-G S-A T-S P P S-G C-S P P S-G C-S Fill in the missing strand T-S P C-S P C-S S-A T-S P P S-G C-S P P S-G C-S The new strands of DNA are in red. 3. The cell will place a C across from every G and a T across from every A. This will complete each missing strand of DNA and create two double helices. 35. Compare and Contrast Natural and Artificial Selection, Give examples to support your answer. Natural Selection occurs when some traits are more successful than others and thus, those genes are passed on at a higher frequency than the less successful genes. Ex. Slow rabbits are eaten more often than fast rabbits, thus more fast rabbit genes are passed on than slow rabbit genes. This creates a generation of rabbits with more fast alleles than the previous generation, In Artificial Selection, humans breed animals so the next generation exhibits the traits we have selected. Ex. Humans breeding dogs with big ears together and not allowing dogs with small ears to contribute their genes to the next generation. Humans can contribute to both artificial and natural selection. For example, humans cutting down only pine trees is NATURAL SELECTION as we are inadvertently affecting the gene pool of those trees by our selections. It is not a purposeful breeding or mating of those trees by us. It is similar to a cheetah eating the slowest gazelles. The cheetah is affecting the genes passed on to future generations and that is natural. The cheetah putting the slow gazelles into cages and only allowing those gazelles to mate would be artificial selection by the cheetah.