bio15

Biology, 6th Edition

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Greg Steinberg Mrs. Wierzbowski AP Biology Chapter 15 The Chromosomal Basis of Inheritance A. Relating Mendelism to Chromosomes a. Basis of Mendelian inheritance i. Traits are separated during meiosis. This trait is known as the chromosome theory of inheritance. b. Tracing Genes i. Thomas Hunt Morgan was the first person to trace a gene to a specific chromosome. ii. Morgan’s research confirmed that Mendel’s heritable factors are on the chromosomes. iii. Morgan used fruit flies in his experiments. iv. Fruit flies produce many offspring with one parental mating. This makes the results more accurate. v. Fruit flies also have only 4 chromosomes that are easy to distinguish. vi. The trait that is most popular in a population is known as the wild type. The mutated version is known as the mutant phenotype. c. Sex Linkage i. When Morgan crossed the F1 generation, he noticed the F2 generation had a sex pattern. All the males had white eyes and the females had red eyes. ii. He concluded that the gene lies on the X chromosome. Since females have an XX combination, they are not affected, but since males have an XY combination, they are. iii. Genes located on a sex chromosome are known as sex linked chromosomes. d. Linked Genes i. Genes that are on the same chromosome are most likely to be carried together as a whole. These genes are known as linked genes. ii. Gray bodies and normal wing size are wild types within fruit flies. iii. Morgan did a test cross that is very similar to Mendel’ test cross. iv. Using his results he saw that the genes tend to stick together and reasoned that the genes must be linked.
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