Biology Chapter 15 Objectives

Biology Chapter 15 Objectives - Chapter 15 The Chromosomal...

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Chapter 15 The Chromosomal Basis of Inheritance Relating Mendelian Inheritance to the Behavior of Chromosomes 1. The observations of cytologists and geneticists provided the basis for the chromosome theory of inheritance. Biologists began to see parallels between the behavior of chromosomes and the behavior of Mendel’s factors during sexual life cycles: Chromosomes and genes are both present in pairs in diploid cells; homologous chromosomes separate and alleles segregate during the process of meiosis; and fertilization restores the paired condition for both chromosomes and genes. According to the chromosome theory of inheritance, Mendelian genes have specific loci, positions, on chromosomes, and it is the chromosomes that undergo segregation and independent assortment. 2. Drosophila melanogaster , a species of fruit flies, is a good experimental organism for genetic studies. The fruit flies are prolific breeders and a single mating will produce hundreds of offspring, and a new generation can be bred every two weeks. Also, fruit flies only have four pairs of chromosomes, which are easily distinguishable with a light microscope. 3. Linked genes do not assort independently since they tend to be inherited together because they are located near each other on the same chromosome. 4. Parental offspring is when an offspring is expected to inherit a phenotype that matches one of the parental phenotypes. However, when nonparental phenotypes are also found among offspring, it is because theses offspring have new combinations of a trait, they are called recombinant types. 5. Crossing over accounts can unlink genes because it breaks the physical connection between genes on the same chromosome. In crossing over, one maternal and one paternal chromatid break at corresponding points and then are rejoined to each other. 6. Sturtevant used the discovery of linked genes and recombination due to cross over in order to construct a genetic map, an ordered list of the genetic loci along a particular chromosome. A genetic map based on recombination frequencies is called a linkage map. He created one based on his assumptions that the farther
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