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Active Lecture PowerPoint ® Presentation for Essentials of Genetics Seventh Edition Klug, Cummings, Spencer, Palladino Copyright © 2010 Pearson Education,

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Presentation on theme: "Active Lecture PowerPoint ® Presentation for Essentials of Genetics Seventh Edition Klug, Cummings, Spencer, Palladino Copyright © 2010 Pearson Education,"— Presentation transcript:

1 Active Lecture PowerPoint ® Presentation for Essentials of Genetics Seventh Edition Klug, Cummings, Spencer, Palladino Copyright © 2010 Pearson Education, Inc. Chapter 4 Modifications of Mendelian Ratios

2 04.01QIn a plant species, if the B allele (blue flowers) and the b allele (white flowers) are incompletely dominant (Bb is light blue), what offspring ratio is expected in a cross between a blue-flowered plant and a white-flowered plant? 1.1/4 blue: 1/2 light blue: 1/4 white 2.1/2 blue: 1/2 white 3.All light blue 4.3/4 blue: 1/4 white 5.1/3 blue: 1/3 light blue: 1/3 white

3 04.01AIn a plant species, if the B allele (blue flowers) and the b allele (white flowers) are incompletely dominant (Bb is light blue), what offspring ratio is expected in a cross between a blue-flowered plant and a white-flowered plant? Answer: 3. All light blue Explanation: The cross is BB  bb, which would yield all Bb (light blue) offspring.

4 04.02QIf a mother has type A blood and her son has type O blood, what are the possible blood types of her son’s father? 1.Type O only 2.Types A or O 3.Types B or O 4.Types A, B, or O 5.Any blood type

5 04.02AIf a mother has type A blood and her son has type O blood, what are the possible blood types of her son’s father? Answer: 4. Types A, B, or O Explanation: The father must carry the I O allele, so he could be I O I O (type O), I A I O (type A), or I B I O (type B).

6 04.03QA cross between two short-tailed mice results in offspring in the ratio of 2/3 short-tailed and 1/3 long- tailed. The best explanation for this result is that 1.two alleles are codominant. 2.there is a recessive lethal allele. 3.there are at least three alleles. 4.there is simple dominance between two alleles. 5.there is a dominant lethal allele.

7 04.03AA cross between two short-tailed mice results in offspring in the ratio of 2/3 short-tailed and 1/3 long- tailed. The best explanation for this result is that Answer: 2. there is a recessive lethal allele. Explanation: A 2:1 ratio indicates a “missing” phenotypic class, suggesting a homozygous (recessive) lethal allele. The cross could be represented as Tt  Tt  1/4 TT (long-tailed), 1/2 Tt (short-tailed), and 1/4 tt (lethal, not observed).

8 04.04QIn a cross between two double heterozygous parents (AaBb), an offspring ratio of 9:3:4 suggests 1.epistasis. 2.epigenesis. 3.sex-linkage. 4.incomplete dominance. 5.codominance.

9 04.04AIn a cross between two double heterozygous parents (AaBb), an offspring ratio of 9:3:4 suggests Answer: 1. epistasis. Explanation: Epistasis involves a nonreciprocal impact of one genetic locus on another. An example is the coat color in mice, as a dihybrid cross would yield 9/16 A-B- agouti, 3/16 aaB- black, and 4/16 (3/16 A-bb, 1/16 aabb) albino.

10 04.05QDuchenne muscular dystrophy is caused by a recessive X-linked allele. A man with this disorder 1.could have inherited it from either parent. 2.must have inherited it from his mother. 3.must have inherited it from both parents. 4.would pass it along to all of his children. 5.would pass it along to only his sons.

11 04.05ADuchenne muscular dystrophy is caused by a recessive X-linked allele. A man with this disorder Answer: 2. must have inherited it from his mother. Explanation: The man must carry only one copy of the allele on his X chromosome that he must have inherited from his mother. He would have inherited a Y chromosome from his father. He would pass that X chromosome on to only his daughters.


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