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 1

2 Patterns of Genetic Inheritance

3 Points to ponder What is the genotype and the phenotype of an individual? What are the genotypes for homozygous recessive and dominant individuals, and a heterozygous individual? Be able to draw a Punnett square for a one-trait cross, two-trait cross, and sex-linked cross. What are Tay-Sachs disease, Huntington disease, sickle- cell disease, and PKU? How are each of these inherited? What is polygenic inheritance? What is a multifactorial trait? What is sex-linked inheritance? Name 3 X-linked recessive disorders. What is codominance? What is incomplete dominance? What do you think about preimplantation genetic testing?

4 These traits are genetically inherited Answer these questions about your inheritance. Do you have a widow’s peak or a straight hairline? Are your earlobes attached or unattached? Do you have short or long fingers? Do you have freckles? 20.1 Genotype and Phenotype

5 Genotype Genotype – specific genes for a particular trait written with _________ –________ are alternate forms of a specific gene at the same position (locus) on a gene (e.g., allele for unattached earlobes and attached lobes); alleles occur in pairs. –A ________ gene will be expressed and will mask a recessive gene (Tt or TT). –A ________ allele is only expressed when a gene has 2 of this type of allele Genotype and Phenotype

6 Genotype –A ___________________ genotype consists of 2 dominant alleles (TT or AA). –A ___________________ genotype consists of 2 recessive alleles (tt or aa). –A _______________ genotype consists of 1 dominant allele and 1 recessive allele (Tt or Aa) Genotype and Phenotype

7 Phenotype Phenotype – the ________________ expression of the genotype Genotype Phenotype EE unattached earlobe Ee unattached earlobe ee attached earlobe What are your genotype and phenotype? 20.1 Genotype and Phenotype

8 Understanding genotype and phenotype Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. sperm egg fertilization growth and development unattached earlobeattached earlobeunattached earlobe Ee eEE ee E eeEE EeeeEE Allele Key E = unattached earlobes e = attached earlobes ee E Figure 20.1 Genetic inheritance affects our characteristics Genotype and Phenotype

9 What about your inheritance? 20.2 One- and Two-Trait Inheritance Figure 20.2 Common inherited traits in humans. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. b. Straight hairline: wwa. Widow’s peak: WW or Ww c. Unattached earlobes: EE or Eed. Attached earlobes: ee e. Shortfingers: SS or Ssf. Long fingers: ss h. No freckles: ffg. Freckles: FF or Ff a: © HFPA, 63 rd Golden Globe Awards; b: © Dynamic Graphics/ PictureQuest RF; c–f: © The McGraw-Hill Companies, Inc. Bob Coyle, photographer; g: © Jupiterimages/ Getty RF; h: © Creatas/PunchStock RF

10 Crosses One-trait cross – considers the inheritance of 1 characteristic e.g. WW x Ww Two-trait cross – considers the inheritance of 2 characteristics e.g. WWTT x WwTT Gametes only carry 1 allele, so if an individual has the genotype Ww, what are the possible gametes that this individual can pass on? Answer: 20.2 One-and Two-Trait Inheritance

11 Another example: 20.2 One-and Two-Trait Inheritance Crosses Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. gametes meiosis Offspring × Parents ff ff no freckles ff

12 Punnett squares Punnett squares are the use of a grid to diagram crosses between individuals by using the ___________________. These allow one to determine the __________ that an offspring will have a particular genotype and phenotype One- and Two-Trait Inheritance

13 Punnett squares Figure 20.3 Expected results of a monohybrid cross One- and Two-Trait Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3 1 fF F f Key F = Freckles f = No freckles Freckles No freckles Phenotypic Ratio 3:1 Freckles No freckles Offspring Ff ffFf FF × Parents Sperm eggs

14 Practicing Punnett squares What would a Punnett square involving a man (M) with a genotype Ff and a woman (F) with a genotype Ff look like? F – freckles f – no freckles M/F F f FFFFf f ff eggs sperm 20.2 One- and Two-Trait Inheritance