Ch14 - Mendel and the Gene Idea Chapter 14 A Quick Review...

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Mendel and the Gene Idea Chapter 14
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A Quick Review of Meiosis In human beings 2n=46. How many chromosomes would you find in a Brain cell? Red blood cell? Egg cell? Sperm cell? Embryonic cell?
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Gregor Mendel
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1 5 4 3 2 Removed stamens from purple flower Transferred sperm- bearing pollen from stamens of white flower to egg- bearing carpel of purple flower Parental generation (P) Pollinated carpel matured into pod Carpel (female) Stamens (male) Planted seeds from pod Examined offspring: all purple flowers First generation offspring (F 1 ) APPLICATION By crossing (mating) two true-breeding varieties of an organism, scientists can study patterns of inheritance. In this example, Mendel crossed pea plants that varied in flower color. TECHNIQUE TECHNIQUE When pollen from a white flower fertilizes eggs of a purple flower, the first-generation hybrids all have purple flowers. The result is the same for the reciprocal cross, the transfer of pollen from purple flowers to white flowers. TECHNIQUE RESULTS Mendel studied pea plants Characters: heritable features, i.e. flower color Trait : a variant of a character, i.e. purple or white Mendel artificially bred pea plants true-breeding : when self-crossed, they always produce the same offspring
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Crossing Plants P generation : parental generation F 1 generation : first filial generation When the parents are both true breeders, the F 1 generation are called hybrids F 2 generation : second filial generation--results from self-fertilization of the F 1 generation P Generation (true-breeding parents) Purple flowers White flowers × F 1 Generation (hybrids) All plants had purple flowers F 2 Generation
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The Law of Segregation 1. Alternative versions of genes account for variations in inherited characteristics White vs. purple flowers These alternative forms are called alleles Allele for purple flowers Locus for flower-color gene Homologous pair of chromosomes Allele for white flowers
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2. For each character, an organism inherits two alleles, one from each parent Remember homologous chromosomes 3. When the two alleles at a locus differ, then one, the dominant allele , determines the organism’s appearance; the other, the recessive allele , has no noticeable effect on the organism’s appearance
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4. (This is referred to as the law of segregation ) The two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes Remember Meiosis--let’s do it out…
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P Generation F 1 Generation F 2 Generation P p P p P p P p Pp PP pp Pp Appearance: Genetic makeup: Purple flower PP White flowers pp Purple flowers Pp Appearance: Genetic makeup: Gametes: Gametes: F 1 sperm F 1 eggs 1 / 2 1 / 2 × Each true-breeding plant of the parental generation has identical alleles, PP or pp .
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Ch14 - Mendel and the Gene Idea Chapter 14 A Quick Review...

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