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Question of the Day Draw a Punnett Square for the following cross: Aa X Aa Punnett Square Agenda • MET Videos • Quiz • Prove me wrong Fig. 14-3-1 EXPERIMENT P Generation (true-breeding parents) Purple flowers White flowers Fig. 14-3-2 EXPERIMENT P Generation (true-breeding parents) F1 Generation (hybrids) Purple flowers White flowers All plants had purple flowers Fig. 14-3-3 EXPERIMENT P Generation (true-breeding parents) F1 Generation (hybrids) Purple flowers White flowers All plants had purple flowers F2 Generation 705 purple-flowered 224 white-flowered plants plants Allele for purple flowers Locus for flower-color gene Fig. 14-4 Allele for purple flowers Locus for flower-color gene Homologous pair of chromosomes Allele for white flowers Definitions • Homozygous—two of the same alleles – Purple and Purple alleles – White and White alleles • Heterozygous—two different alleles – One Purple and one white allele • Genotype—combination of alleles • Phenotype—expression of alleles Fig. 14-5-1 P Generation Purple flowers White flowers Appearance: Genetic makeup: PP pp Gametes: P p Fig. 14-5-2 P Generation Purple flowers White flowers Appearance: Genetic makeup: PP pp Gametes: p P F1 Generation Appearance: Genetic makeup: Gametes: Purple flowers Pp 1/ 2 P 1/ 2 p Fig. 14-5-3 P Generation Purple flowers White flowers Appearance: Genetic makeup: PP pp Gametes: p P F1 Generation Appearance: Genetic makeup: Gametes: Purple flowers Pp 1/ 2 1/ 2 P Sperm F2 Generation P p PP Pp Pp pp P Eggs p 3 1 p Dominance in Humans • Tongue rolling dominant to nonrolling • Cleft chin dominant to smooth chin Dominance in Humans • Widows peak dominant to straight hairline • Unattached earlobes dominant to attached earlobes Law of Segregation 1. Different alleles cause variation in a popluation 2. For each trait, an organism inherits two alleles…one from each parent 3. If the two alleles differ, then one, the Dominant allele is fully expressed 4. The two alleles for each trait separate prior to sex The Law of Segregation cont’d • The two alleles for each trait are separated prior to sex • Example: Heterozygote • Purple color is separated from white color and each allele is passed on separately to the baby Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings The Law of Independent Assortment • When chromosomes are ripped apart prior to sex, the traits are sorted independently from one another • Example: – Having a cleft chin does not mean that you will always have attached earlobes Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Dominantly Inherited Disorders • Some human disorders are caused by dominant alleles • Dominant alleles that cause a lethal disease are rare and arise by mutation • Achondroplasia is a form of dwarfism caused by a rare dominant allele Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 14-17 Parents Dwarf Dd Normal dd Sperm D d d Dd Dwarf dd d Dd Dwarf Eggs Normal dd Normal How can two dwarfs have children that are not dwarfs? • Homozygous dominant is lethal • Heterozygous in non-lethal • Homozygous recessive is non-dwarf Punnett Square Autosomes vs. Sex Chromosomes Key 1st generation 1 normal male 2 normal female male with condition 2nd generation 1 2 1 2 3 4 5 3 4 3rd generation female with condition Sex chromosomes • • Sex determined by XX and XY Sex linked traits – Hemophilia • X linked recessive Hemophilia Punnett Square Based on the diagram below, what do you know about individual III-2's mother? Objectives • Demonstrate content knowledge of genetics • Work collaboratively with your peers • Discuss ideas and form a consensus • Self-evaluate your work
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