20_Chromosome inheritance I&II_forupload

20_Chromosome inheritance I&II_forupload - The...

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Unformatted text preview: The Chromosomal Basis of Inheritance Mendelian inheritance has its physical basis in the behavior of chromosomes • Several researchers proposed in the early 1900s that genes are located on chromosomes • The behavior of chromosomes during meiosis was said to account for Mendel’s laws of segregation and independent assortment • The chromosome theory of inheritance states that: – Mendelian genes have specific loci (positions) on chromosomes – It is the chromosomes that undergo segregation and independent assortment Mendelian inheritance has its physical basis in the behavior of chromosomes 0.5 mm Meiosis Metaphase I Anaphase I Metaphase II Gametes LAW OF SEGREGATION The two alleles for each gene separate during gamete formation. LAW OF INDEPENDENT ASSORTMENT Alleles of genes on nonhomologous chromosomes assort independently during gamete formation. 1 4 yr 1 4 Yr 1 4 YR F 1 Generation 1 4 yR R R R R R R R R R R R R Y Y Y Y Y Y Y Y Y Y Y Y y r r r r r r r r r r r r y y y y y y y y y y y All F 1 plants produce yellow-round seeds (YyRr) 1 2 2 1 Morgan’s Experimental Evidence: Scientific Inquiry • The first solid evidence associating a specific gene with a a specific chromosome came from Thomas Hunt Morgan, an embryologist • Morgan’s experiments with fruit flies provided convincing evidence that chromosomes are the location of Mendel’s heritable Morgan’s Choice of Experimental Organism • Characteristics that make fruit flies a convenient organism for genetic studies: – They breed at a...
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20_Chromosome inheritance I&II_forupload - The...

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