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Chapter 9 Introduction to Genetics

Chapter 9 Introduction to Genetics. Gregor Mendel (Father of Genetics). Was the first person to analyze patterns of inheritance Deduced the fundamental principles of genetics. Figure 9.4. Seven characteristics of pea plants studied by Mendel. Dominant. Recessive. Recessive. Dominant.

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Chapter 9 Introduction to Genetics

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  1. Chapter 9Introduction to Genetics

  2. Gregor Mendel (Father of Genetics) • Was the first person to analyze patterns of inheritance • Deduced the fundamental principles ofgenetics Figure 9.4

  3. Seven characteristics of pea plants studied by Mendel Dominant Recessive Recessive Dominant Pod shape Flower color Constricted Inflated White Purple Pod Color Yellow Green Flower position Axial Terminal Stem length Seed color Yellow Green Tall short Figure 9.7 Seed shape Wrinkled Round

  4. Mendel’s Garden • Mendel studied garden peas • These plants are easily manipulated • Self-fertilize Stamen pistil Figure 9.5

  5. Removed stamens from purple flower White • Mendel carried out some cross-fertilization Stamens Parents (P1) Transferred pollen from stamens of white flower to pistil of purple flower pistil Pollinated ovary matured into pod Planted seeds from pod Offspring (F1) Figure 9.6

  6. Cross Fertilization of Parents Pollen Cross-Fertilize Pollen P P True-breedingPurple-floweredParent True-breedingWhite-floweredParent F1 All Purple-floweredOffspring (hybrid)

  7. Monohybrid cross – cross between hybrids for one trait such as flower color F1 75% Purple25% White Self-Fertilize F2 F2 F2 F2

  8. Genes, Alleles, Loci (specific location on a chromosome where a gene is found)and Chromosomes Loci: Loci: 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 11 11 12 12 13 13 14 14 15 15 16 16 17 17 18 18 19 19 20 20 21 21 22 22 23 23 24 24 25 25 26 26 Chromosome from One Parent t C F locus has gene that controls leaf color. Plant homozygous dominant for this gene locus has gene that controls plant height. Plant homozygous recessive for this gene locus has gene that controls fruit shape. Plant heterozygous for this gene t f C Homologous Chromosome from Other Parent

  9. Using a Testcross to Determine an Unknown Genotype • A testcross is a mating between • and individual of unknown • genotype and • a homozygous • recessive individual Testcross: Genotypes P_ pp Two possibilities for the purple flower: Pp PP P Gametes p P p P pp Pp Pp Offspring All purple 1 purple : 1 white Figure 9.12

  10. Rules of Probability • Probability affects inheritance (Example) • Coin toss: probability of heads = ½, the outcome of any particular toss is unaffected by what happened on previous attempts. • Each toss is an independent event • The probability of a compound event is the product of the separate probabilities of the independent events. (example: ½ x ½ = ¼) • Rule of Multiplication

  11. The Rules of Probability F1 Genotypes B b male B b female • The rule of multiplication Formation of eggs Formation of sperm • The probability of a compound event is the product of the separate probabilities of the independent events 1/2 B B 1/2 1/2 B B b b 1/4 1/2 (1/2  1/2) b B B b 1/4 1/4 b b F2 Genotypes 1/4 Figure 9.13

  12. Dihybrid Cross:SsYy X SsYy SsYy x SsYy Eggs SsYy Parent Self-fertilizes 14 14 14 14 SY Sy sY sy SY 14 116 116 116 116 Key: Smooth = S Wrinkled = s Yellow = Y Green = y SSYY SSYy SsYY SsYy Sy 14 116 116 116 116 SSyY SSyy SsyY Ssyy Sperm sY 14 116 116 116 116 sSYY sSYy ssYY ssYy sy 14 116 116 116 116 sSyY sSyy ssyY ssyy

  13. Family Pedigrees Recessive Traits Dominant Traits • Mendel’s principles apply to the inheritance of many human traits Freckles No freckles Straight hairline Widow’s peak Free earlobe Attached earlobe Figure 9.14

  14. Incomplete Dominance: • Inheritance in which, an active allele does not entirely compensate for an inactive allele • When the heterozygous is intermediate between the two homozygous phenotypes • Example: Carnations and snap dragons

  15. Codominance: • Condition in which both alleles of a gene are expressed • Both phenotypes are expressed in heterozygous • Example: Hair color in cows and sickle Cell anemia

  16. Multiple Alleles: • Traits that are expressed by more than two alleles • Alleles arise through mutations, and the same gene in different individuals may have different mutations, each producing a new allele • You can find dozens of alleles for every gene • Most genes have multiple alleles rather that just two • Examples: Blood types

  17. Polygenic Inheritance • Interactions of many genes. Alleles at several even many sites on a chromosome affect each characteristic. • Not governed by a single gene • Interactions of two or more genes contribute to a single phenotype • Example: Eye color • The color of the human iris varies from pale blue through green to almost; black • Blue = little or no pigment • Green, brown, hazel, and black (have more pigment, have genes that direct the production of more melanin

  18. Environmental Influences • An organism is not just the sum of it’s genes, in addition to genotype, the environment in which an organism lives affects it’s phenotype • Example: Himalayan Rabbit • skin color, and • human intelligence (identical twins raised in different environments, have different IQ”s)

  19. Recombination Can Create New Combinations of Linked Alleles • Although they tend to be linked together, genes in the same chromosomes do not always stay together • Recombination occurs due to crossing over • Crossing over during Meiosis explains the appearance of new combinations

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