biol1201 test 3 notes part b

biol1201 test 3 notes part b - Genetics Mendelian Genetics...

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Genetics- Mendelian Genetics Gregor Mendel o Born in 1822 o Monk at the monastery at St. Thomas in Brunn, Czech Republic o Trained in botany, mathematics and physics o In 1866 published his work “Experiments in Plant Hybirds” o 1900 Mendel’s works was rediscovered y Hugo de Vries in Holland; Carl Correns in Germany, and Erich von Tschermak in Austria o “Particulate” rather than “blending” inheritance o Mendel worked with pea plants-there was a long history of previous work on peas. o Why did Mendel succeed and others fail? John Goss o English in 1824 worked with the same plants 30 years before Mendel began his work o He observed green and yellow seeds in peas, followed them through a number of generations o He observed what Mendel saw Today we speak of Mendelian genetics NOT Gossian genetics o Why?- Goss didn’t count and record number of seeds Why did Mendel succeed? o He chose the right organism to work with, the edible pea plant - The plant usually self-pollinates (self fertilizes) - Stigma and anthers are completely enclosed by petals until after fertilization - Therefore there is no cross contamination - Figure 14.2 o He picked the “right” traits to follow o He followed the crosses for several generations o He was quantitative in his observations o He had a little help from his friends o Figure 14.3, 14.4 -Gene- discrete unit of hereditary information consisting of a specific sequence of DNA; Often codes for a polypeptide chain - Gene locus- a particular position along a specific chromosome where a given gene is located - Allele - an alternative form of a gene (Examples: A, a; B, b) - Homozygous - having two identical alleles for a trait (AA, aa, ii) - Heterozygous - having two different genes (alleles) for a trait (Aa) - Genotype - the genetic makeup of an individual - Phenotype - the physical manifestation of a trait (how it appears); determined by the genotype - Dominant allele - allele that is fully expressed in the phenotype of a heterozygote; only a single copy is required to express the trait; Represented by a capital letter - Recessive allele- in a heterozygous individual the allele that is completely masked out (not expressed) in the phenotype; represented by a lowercase letter Why isn’t the recessive allele expressed? -Inactive or defective enzyme Generations o P - parental o F1 - Filial one- offspring of the parental generation- hybrids
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o F2 - Filial two- offspring of cross between F1 (hybrid) individuals Figure 14.5/ 14.6 Mendel’s First Law o The two members of a gene pair segregate (separate) from each other into the gametes o Each gamete carries one member of the gene pair When does Mendelian segregation occur? o When do homologous chromosomes separate? o Anaphase I of meiosis o Alleles segregate into different gametes o Test cross Figure 14.7- two possible outcomes: unknown ( homozygous dominant ) all offspring display the dominant trait; unknown ( heterozygous ) half the offspring display the dominant trait, half the offspring display the recessive trait -Incomplete dominance
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