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1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Human Biology Sylvia S. Mader Michael Windelspecht Chapter.

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Presentation on theme: "1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Human Biology Sylvia S. Mader Michael Windelspecht Chapter."— Presentation transcript:

1 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Human Biology Sylvia S. Mader Michael Windelspecht Chapter 20 Patterns of Genetic Inheritance Lecture Outline Part 2

2 2 Practicing ratios _____________ is the number of offspring with the same genotype. _____________ is the number of offspring with the same outward appearance One- and Two-Trait Inheritance

3 3 Practicing ratios What is the genotypic ratio? 1: 2: 1 (1 FF: 2 Ff: 1 ff) What is the phenotypic ratio? 3: 1 (3 with freckles and 1 with no freckles) M/F F f FFFFf f ff eggs sperm 20.2 One- and Two-Trait Inheritance

4 4 Monohybrid crosses Monohybrid cross – an experimental cross in which parents are identically heterozygous at 1 gene pair (e.g., Aa x Aa) Figure 20.4 Determining if a dominant phenotype is homozygous or heterozygous One- and Two-Trait Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ww W W 1 1 × ww W w Offspring Parents wwWW × Parents Wwww Ww ww Offspring ww Ww eggs Straight hairline Widow’s peak Phenotypic Ratio 1:1 Straight hairline Widow’s peak Straight hairline Widow’s peak Key W = w = Widow’s peak Straight hairline Widow’s peak W = w = Key Phenotypic Ratio Widow’s peakAll Ww Sperm a.b.

5 5 Possible gametes for 2 traits Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. SS WW ss ww WW ww WW WWWWwwww WWwwww ss sss ss ss s SS S SSSS SSS WSwswSWs Cell has two pairs of homologues. one pair oreither MEIOSIS I MEIOSIS II Allele Key s = Long fingers S = Short fingers w = Straight hairline W = Widow’s peak Figure 20.5 Meiosis results in genetic diversity of gametes One- and Two-Trait Inheritance

6 6 Dihybrid cross (a type of two- trait cross) Dihybrid cross – an experimental cross usually involving parents who are ______________ for different alleles of 2 genes –Results in a 9:3:3:1 genotypic ratio for the offspring Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. P generation P gametes F 1 generation WwSs wwss WWSS ws WS × Figure 20.6 Expected results of a dihybrid cross One- and Two-Trait Inheritance

7 7 Punnett square for a dihybrid cross What would the Punnett square look like for a dihybrid cross between a male who is WWSS and a female who is wwss? Figure 20.6 Expected results of a dihybrid cross One- and Two-Trait Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. sperrm w s P generation P gametes F 1 generation F 1 gametes F 2 generation WWSSwwss WS ws WwSs oocytes WSWswSws WS WWSSWWSsWwSSWwSs Ws WWSsWWssWwSsWwss WwSSwwSSwwSs wS Offspring wwSsWwSsWwss Widow’ speak, short fingers Widow’ speak, long fingers Straight hairline, short fingers Straight hairline, long fingers Phenotypic Ratio = Long fingers = Short fingers = Straight hairline = Widow’s peak Allele Key WwSs wwss W w S s

8 8 Two-trait cross Figure 20.7 Two-trait cross One- and Two-Trait Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Widow’ speak, short fingers Widow’ speak, long fingers Straight hairline, short fingers Straight hairline, long fingers Phenotypes = Long fingers = Short fingers = Straight hairline = Widow’s peak Key Offspring Parents WwSs Wwss wwSs WS Ws wS ws wwssWwSs eggs ws sperm × wwss W w S s

9 9 Phenotypic ratios of common crosses Table 20.1 Phenotypic ratios of common crosses 20.2 One- and Two-Trait Inheritance

10 10 Preimplantation genetic diagnosis If prospective parents carry an allele for a genetic disorder, they may seek assurance that their offspring will be free of the disorder Following in vitro fertilization (IVF), the zygote divides. When the embryo has 8 cells, 1 may be removed for genetic testing. Only embryos that will not have the genetic disorders of interest are placed in the uterus to continue developing One- and Two-Trait Inheritance

11 11 Figure 20A The process of preimplantation genetic diagnosis One- and Two-Trait Inheritance Preimplantation genetic diagnosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8-cell embryo Embryo develops normally in uterus. Embryo develops normally in uterus. b. Testing the egga. Testing the embryo Polar body has genetic defect. egg Woman is heterozygous. Embryonic cell is removed. Egg is genetically healthy. egg nucleus sperm nucleus Cell is genetically healthy. (both): © Brand X/SuperStock RF

12 12 Autosomal recessive disorder Individuals must be homozygous recessive to have the disorder Inheritance of Genetic Disorders Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. II III IV I aa A? Aa A?aa Aa * relatives Aa Key = affected Aa = carrier (unaffected) AA = unaffected A? = unaffected (one allele unknown) aa AaA? Autosomal recessive disorders Affected children can have unaffected parents. Heterozygotes (Aa) have an unaffected phenotype. Two affected parents will always have affected children. Affected individuals with homozygous unaffected mates will have unaffected children. Close relatives who reproduce are more likely to have affected children. Both males and females are affected with equal frequency. Figure 20.8 Autosomal recessive disorder pedigree.

13 13 Autosomal dominant disorder Individuals that are homozygous dominant and heterozygous will have the disorder. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. aa = unaffected (one allele unknown) = affected AA Aa A? Autosomal dominant disorders Affected children will usually have an affected parent. Heterozygotes (Aa) are affected. Two affected parents can produce an unaffected child. Two unaffected parents will not have affected children. Both males and females are affected with equal frequency. III II I Aa aa Aa * A?aa Aa Key Figure 20.9 Autosomal dominant disorder pedigree Inheritance of Genetic Disorders


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