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Observable Patterns of Inheritance. Can you do this?. Probability True-breeding Hybrid Segregation Traits Genes. Homozygous Heterozygous Phenotype Genotype Dominant Recessive. Terms to Know. Genes. Chemical factors that determine traits (units of information)
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Probability True-breeding Hybrid Segregation Traits Genes Homozygous Heterozygous Phenotype Genotype Dominant Recessive Terms to Know
Genes • Chemical factors that determine traits (units of information) • Analogy: Genes are like a combination of ingredients in a recipe. They code for a specific food. • Passed from parents to offspring • Each has a specific location (locus) on a chromosome
Alleles • Different forms of a gene (back to analogy…replacing jiffy p.b. with skippy p.b.) • Dominant allele (Uppercase letter) overrules a recessive allele (lowercase letter) that it is paired with
Allele Combinations • Homozygous =purebred • having two identical alleles at a locus • AA (dominant expressed) or aa (recessive expressed) • Heterozygous =hybrid • having two different alleles at a locus • Aa (dominant expressed)
Genotype & Phenotype • Genotype refers to particular genes an individual carries • Phenotype refers to an individual’s observable traits • Cannot always determine genotype by observing phenotype
Tracking Generations • Parental generation P mates to produce • First-generation offspring F1 mate to produce • Second-generation offspring F2
Earlobe Variation • Whether a person is born with attached or detached earlobes depends on a single gene • Gene has two molecular forms (alleles)
Earlobe Variation • You inherited one allele for this gene from each parent • Dominant allele specifies detached earlobes (E) • Recessive allele specifies attached earlobes (e)
Dominant & Recessive Alleles • If you have attached earlobes, you inherited two copies of the recessive allele • If you have detached earlobes, you may have either one or two copies of the dominant allele
Early Ideas About Heredity • People knew that sperm and eggs transmitted information about traits • Blending theory • Problem: • Would expect variation to disappear • Variation in traits persists
Gregor Mendel Strong background in plant breeding and mathematics Using pea plants, found indirect but observable evidence of how parents transmit genes to offspring
Mendel was born in1822 • Austrian monk • Studied at the Univ. of Vienna • Teacher (High School)
Figure 24–5 The Structure of a Flower Stamen Carpel Stigma Anther Style Filament Ovary Petal Ovule Sepal Section 24-1
The Garden Pea Plant • Self-pollinating • True breeding (different alleles not normally introduced) • Can be experimentally cross-pollinated
F M Dominant trait is expressed Recessive appears
Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants Seed Shape Seed Color Seed Coat Color Pod Shape Pod Color Flower Position Plant Height Round Yellow Gray Smooth Green Axial Tall Wrinkled Green White Constricted Yellow Terminal Short Round Yellow Gray Smooth Green Axial Tall
F1 Results of Mendel’s Dihybrid Crosses • All plants displayed the dominant form of both traits • We now know: • All plants inherited one allele for each trait from each parent • All plants were heterozygous (AaBb)
Principle of Dominance • Some alleles are dominant and others are recessive.
Mendel wanted to know if the recessive alleles disappeared or are they still in the f1,just hidden.
Principles of Dominance P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short
Principles of Dominance P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short
Principles of Dominance P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short
Mendel’s Theory of Segregation • An individual inherits a unit of information (allele) about a trait from each parent • During gamete formation, the alleles segregate from each other
Independent Assortment • Mendel concluded that the two “units” for the first trait were to be assorted into gametes independently of the two “units” for the other trait • Members of each pair of homologous chromosomes are sorted into gametes at random during meiosis
Independent Assortment Metaphase I OR A A a a A A a a B B b b b b B B Metaphase II: A A a a A A a a B B b b b b B B Gametes: B B b b b b B B A A a a A A a a 1/4 AB 1/4 ab 1/4 Ab 1/4 aB
The physical characteristic Type of alleles
Impact of Mendel’s Work • Mendel presented his results in 1865 • Paper received little notice • Mendel discontinued his experiments in 1871 • Paper rediscovered in 1900 and finally appreciated
Probability • The likelihood that a particular event will occur. • Flip a coin. • We use Punnett Squares
D 38- Deduce the probable mode of inheritance of traits (e.g.,
Homozygous recessive Homozygous recessive a a a a A A Aa Aa Aa Aa a A aa Aa aa Aa Punnett Squares of Test Crosses Two phenotypes All dominant phenotype
Female gametes A a A AA Aa Male gametes a Aa aa Punnett Square of a Monohybrid Cross Dominant phenotype can arise 3 ways, recessive only one
Test Cross • Individual that shows dominant phenotype is crossed with individual with recessive phenotype • Examining offspring allows you to determine the genotype of the dominant individual
Genetics Practice Problem 1 • What occurs when a purple plant that is heterozygous is fertilized by a white plant? • Identify generations • Punnett Square • Genotypes % • Phenotype %
Principle of Independent Assortment • The genes for different traits separate independently of one another during the formation of gametes.
Yellow round 9/16 • Green round 3/16 • Yellow wrinkled 3/16 • Green wrinkled 1/16 • 9 : 3 : 3 : 1 Ratio
Dihybrid Cross Experimental cross between individuals that are homozygous for different versions of two traits
Straight Pinky (Dominant) Bent Pinky (Recessive) Straight Thumb (Dominant) Curved Thumb (Recessive)
More Dominant Traits Polydactylism Achondroplastic Dwarfism Tay-Sachs Disease - One Wrong Letter