Module 4 Notestothesixth

Module 4 Notestothesixth - Mendel discovered the basic...

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Mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experiments Advantages of pea plants for genetic study: o Varieties with distinct heritable variable characters (such as flower color); o Mating can be controlled o Each pea plant has sperm-producing organs (stamens) P was the parental generation and F1 is the first filial generation (first generation of offspring from the parental generation) o Use "true breeders" which were plants that would always produce the same color flower when they were self-pollinated The "true breeders" were homozygous for the genes that coded for flower color Ex: PP=purple pp=white In a typical experiment Mendel mated two contrasting true-breeding parents to produce hybrids, or heterozygote's (Pp) o When each hybrid was self pollinated they could produce purple or white flowers o There was usually a 3:1 ratio for purple to white flowers Mendel called the purple flower a dominant trait and the white flower color was a recessive trait Developed a hypothesis to explain the 3:1 inheritance patter he observed in F2 o The first concept is that alternative versions of genes account for variations in inherited characters-alleles We know now that each gene resides at a specific locus on a specific chromosome o Figured out that there were two alleles that determined the genotype and thus determined the phenotype The allele is the variation of it, the gene is the location on the chromosome, and the chromosome is where the gene is found. The second concept is that for each character an organism inherits two alleles, one from each parent o Homozygous the same heterozygote different The third concept is that if two alleles at a locus differ, then one (the dominant allele) determines the organisms appearance, and the other (the recessive allele) has no noticeable effect on appearance The fourth concept the law of segregation, states that the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes o Thus, an egg or sperm gets only one of the two alleles that are present in the somatic cells of an organism The possible combinations of sperm and egg can be shown using a Punnett square
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Mendel's segregation model accounts for the 3:1 ratio he observed in the F2 generation of his numerous experiments How can we tell the genotype of an individual with the dominant phenotype? o We would determine it doing a test cross: breeding the mysterious individual with a white homozygous individual. If it was a heterozygote there will be a 1:1 ratio of white and purple flowers and if it was a homozygote it will only breed purple flowers Mendel derived the law of segregation by following a single character (monohybrid cross) The F1 offspring produced in this cross were monohybrids, individuals that are heterozygous for one character The genotype for one trait is not determined by another trait
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Module 4 Notestothesixth - Mendel discovered the basic...

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