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Session 10 (Genetics)

Session 10 (Genetics) - MCB 181 Study Session 10(Genetics...

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MCB 181 Study Session 10 (Genetics)
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Learning Goals for Study Session 10 (Genetics) Be able to describe how Mendel made genetic crosses with pea plants, and why he was successful. Describe Mendel’s conclusions from his experiments and relate them to the separation of homologous chromosomes during meiosis leading to gamete formation. Be able to define genetic terms such as allele, homozygous, heterozygous, dominant, recessive, phenotype, genotype, parental, F1 and F2 generations, epitasis, pleitrophy, aneuploid, monosomic and trisomic. Use the Punnett square to predict the genotype and phenotype from a monohybrid or dihybrid cross between homozygous or heterozygous parents. Be able to use a test cross to determine an unknown genotype and explain why this procedure is not used in human genetics. Be able to relate Mendel’s first and second laws to events that occur during meiosis. Be able to explain how recombinant phenotypes arise and how their frequency is used to map genes on a chromosome. Briefly describe some factors that lead to complications of simple Mendelian genetic principles. Explain what is meant by the term nondisjunction and explain the consequences for humans.
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Genetics and Mendel Genetics is the science of heredity or how traits are transmitted from parents to offspring. Our modern understanding of genetic inheritance began with the studies of Gregor Mendel (1822- 1884), a monk who lived in what is now the Czech Republic. Mendel worked in an Abby garden growing the common garden pea plant and discovered simple (Mendelian) principles of “transmission genetics” that apply to all organisms that reproduce sexually.
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What did Mendel do? Mendel identified several heritable features referred to as characters (e.g. flower color, seed or pod color or shape, and stem length) in garden pea plants ( Pisum sativum ). He studied variations in the characters called traits (e.g. purple or white flowers, yellow or green pods, etc.) by doing controlled mating or breeding of pea plants. The keys to his success were: 1. He started with genetically uniform (true breeding) varieties. 2. He was able to exactly control which plants mated with each other. 3. He examined many genetic crosses and obtained statistically valid results.
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What does “true breeding” mean? Diploid cells have two sets of chromosomes, one set from each parent in homologous pairs. A homologous chromosome pair (illustrated to the right) has genes for the same character (flower color in this example), although the pair may have different versions or alleles of the gene (purple or white flowers in this example) at a given location ( locus) on the chromosome. True breeding plants are genetically uniform because they have the same version of the gene (i.e. identical alleles) for a given character on homologous chromosomes .
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How do you control mating in pea plants?
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