BIOLOGY I Study Guide # 5: Topic Genetics 1

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1 BIOLOGY I Study Guide # 5: Topic Genetics 1 Biology Textbook pg , Name: I. Mendelian Genetics (pg ) Define: a. genetics: b. fertilization: c. true-breeding: d. trait: e. hybrid: f. gene: g. allele: h. segregation: i. phenotype: j. genotype: k. heterozygous: l. homozygous: Matching: On the lines provided, write the letter of the definition of each term. 1. genetics a. likelihood that something will happen 2. trait b. process by which the number of chromosomes per cell is cut in half 3. hybrid c. specific characteristic 4. gene d. offspring of crosses between parents with different traits 5. allele e. containing a single set of chromosomes 6. gamete f. sex cell 7. probability g. factor that determines traits 8. Punnett square h. diagram showing possible gene combinations 9. haploid i. the scientific study of heredity 10. meiosis j. form of a gene Explain the following principles of inheritance according to Gregor Mendel: 1. Principle of dominance: 2. Principle of segregation: 3. Principle of independent assortment: Complete the following: 1. Circle the letter of each sentence that is true about Mendel s principles. a. The inheritance of biological characteristics is determined by genes that are passed from parents to their offspring. b. Two or more forms of the gene for a single trait can never exist. c. The copies of genes are segregated from each other when gametes are formed. d. The alleles for different genes usually segregate independently of one another. 2. When two or more forms of the gene for a single trait exist, some forms of the gene may be and others may be.

2 3. Although organisms with the same physical characteristics have the same, they might have different, or genetic makeup. 4. When Mendel allowed the tall F1 pea plants (Tt) to self-pollinate, a. some of the offspring were short. b. the offspring were of medium height. c. all of the offspring were tall. 5. Two plants with the genotypes TT and Tt a. would have the same phenotype. b. would have different phenotypes. c. have all dominant alleles. 6. In humans, being a tongue roller (R) is dominant over non-roller (r). A man who is a non-roller marries a woman who is heterozygous for tongue rolling. Father s phenotype Father s genotype Mother s phenotype Mother s genotype What is the probability of this couple having a child who is a tongue roller? Show the cross using the Punnett square provided. 7. In guinea pigs, the allele for a rough coat (R) is dominant over the allele for a smooth coat (r). A heterozygous guinea pig and a homozygous recessive guinea pig have a total of nine offspring. Explain how all nine offspring can have smooth coats. 8a. In a two-factor cross, Mendel followed different genes as they passed from one generation to the next. 8b. Write the genotypes of the true-breeding plants that Mendel used in his two-factor cross. Phenotype Genotype a. round yellow peas b. wrinkled green peas 8c. Circle the letter that best describes the F1 offspring of Mendel s two-factor cross. a. Homozygous dominant with round yellow peas c. Heterozygous dominant with round yellow peas b. Homozygous recessive with wrinkled green peas d. Heterozygous recessive with wrinkled green peas 8d. How did Mendel produce the F2 offspring? 8e. Complete the Punnett square below to show the predicted results of Mendel s two-factor cross. 8f. What were the phenotypes of the F2 generation that Mendel observed? 8g. What did Mendel observe in the F2 offspring that showed him that the alleles for seed shape segregate independently of those for seed color?

3 V. Patterns of Inheritance (pg ) 1. What is the difference between a heterozygous phenotype produced by incomplete dominance and a heterozygous phenotype produced by codominance? 2. Complete the table of the different patterns of inheritance. Type Description Examples One allele is not completely dominant over another. The heterozygous phenotype is somewhere in between the two homozygous phenotypes. Both alleles contribute to the phenotype of the organism. Genes have more than two alleles. Two or more genes control a trait. 3. List three criteria Thomas Hunt Morgan was looking for in a model organism for genetic studies. a. b. c. 4. Characteristics are determined by interaction between genes and the. VI. Linkage and Gene maps (pg ) 1. Linked genes a. are never separated. c. are on the same chromosome. b. assort independently. d. are always recessive. 2. Explain why it is chromosomes, not individual genes, that assort independently: 3. Which of the following shows the relative locations of each known gene in an organism? a. polygenic trait b. gamete c. Punnett square d. gene map 4. Gene maps are based on a. the frequencies of crossing-over between genes. b. independent assortment. c. genetic diversity. 5. If two genes are on the same chromosome and rarely assort independently, a. crossing-over never occurs between the genes. c. the genes are probably located far apart from each other. b. crossing-over always occurs between the genes. d. the genes are probably located close to each other. 6. Explain how linkage is used to make gene maps. 7. Three genes, stumpy (S), mottled (M), and pale (P) are found on the same chromosome in a newly discovered species of fly. A preliminary gene map places gene S in the middle, with M and P on opposite sides. The frequency of genetic recombination between genes M and S is 5%, which means that a cross-over occurs between these two genes in meiosis 5% of the time (one gamete in 20 has a cross-over). The frequency between genes S and P is 8%. Which gene is closer to S gene P or gene M?

4 VII. The Human Genome (pg ) 1. Define: a. karyotype: b. sex chromosome: c. autosome: d. pedigree chart: e. sex-linked genes: f. nondisjunction: 2. How many chromosomes are shown in a normal human karyotype? a. 46 b. 23 c In humans, a male has a. two X chromosomes. b. one X chromosome and one Y chromosome. c. two Y chromosomes. 4. Human females produce egg cells that have a. one X chromosome. b. two X chromosomes. c. one X or one Y chromosome. 5. A pedigree can be used to a. determine whether an allele is dominant or recessive. c. determine whether a trait is inherited. b. show how a trait is passed from one generation to the next. d. all of the above 6. The pedigree below (Figure 1) shows the inheritance of free earlobes and attached earlobes in five generations of a family. Attached earlobes is caused by a recessive allele (f). a. Is individual 2 in Figure 1 homozygous or heterozygous for free earlobes? Explain. b. In Figure 1, how many children of individuals 4 and 5 have attached earlobes? c. Can you be certain of the genotype of individual 5 in Figure 1? Explain. d. Predict the genotype and phenotype of individual 14 in Figure 1. e. In Figure 1, are any of the descendents of individuals 1 and 2 homozygous for free earlobes? Explain your answer. 7. What does it mean when a trait is said to be sex-linked?

5 8. Why are sex-linked diseases more common in males than in females? 9. Explain why the father of a girl who is colorblind must also be colorblind. 10. What occurs during nondisjunction? 11. A man who does not have hemophilia and a woman who is a carrier of the disorder have a son. What is the probability that their son has hemophilia? Explain or show. 12. Scientists test for alleles that cause human genetic disorders by a. making karyotypes. b. making DNA fingerprints. c. using DNA probes. 13. The Human Genome Project is an attempt to a. make a DNA fingerprint of every person s DNA. b. analyze the human DNA sequence. c. cure human diseases. 14. The purpose of gene therapy is to a. cure genetic disorders. b. determine the sequences of genes. c. search for genes on chromosomes. 15. The sequencing of human chromosomes 21 and 22 showed that a. some regions of chromosomes do not code for proteins. b. all of the DNA of chromosomes codes for proteins. c. different chromosomes have the same number of genes. 16. Which of the following form(s) a Barr body? a. the Y chromosome in a male cell b. the X chromosome in a male cell c. one of the X chromosomes in a female cell 17. Because the X chromosome contains genes that are vital for normal development, no baby has been born a. with one X chromosome. c. without an X chromosome. b. with three X chromosomes. d. with four X chromosomes. 18a. There are alleles for the ABO blood group. They are,, 18b. Is it possible for a person with blood type alleles I A and I B to have blood type A? Explain. 19. What type of picture would a biologist look at to determine whether a fetus has Down syndrome? What abnormality would he find out? 20. One example of a sex-linked disorder is a. sickle cell disease. b. hemophilia c. Down syndrome. d. Tay-Sachs disease.