TAILIEUCHUNG - Lecture Biology (7th edition) - Chapter 15: The chromosomal basis of inheritance

This chapter explain the chromosomal theory of inheritance and its discovery, explain why sex-linked diseases are more common in human males than females, distinguish between sex-linked genes and linked genes, explain how meiosis accounts for recombinant phenotypes, explain how linkage maps are constructed,. | Chapter 15 The Chromosomal Basis of Inheritance Overview: Locating Genes on Chromosomes Genes Are located on chromosomes Can be visualized using certain techniques Figure Concept : 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 on chromosomes Chromosomes undergo segregation and independent assortment The chromosomal basis of Mendel’s laws Figure Yellow-round seeds (YYRR) Green-wrinkled seeds (yyrr) Meiosis Fertilization Gametes All F1 plants produce yellow-round seeds (YyRr) P Generation F1 Generation Meiosis Two equally probable arrangements of chromosomes at metaphase I LAW OF SEGREGATION LAW OF INDEPENDENT ASSORTMENT Anaphase I Metaphase II Fertilization among the F1 plants 9 : 3 : 3 : 1 1 4 1 4 1 4 1 4 YR yr yr yR Gametes Y R R Y y r r y R Y y r R y Y r R y Y r R Y r y r R Y y R Y r y R Y Y R R Y r y r y R y r Y r Y r Y r Y R y R y R y r Y F2 Generation Starting with two true-breeding pea plants, we follow two genes through the F1 and F2 generations. The two genes specify seed color (allele Y for yellow and allele y for green) and seed shape (allele R for round and allele r for wrinkled). These two genes are on different chromosomes. (Peas have seven chromosome pairs, but only two pairs are illustrated here.) The R and r alleles segregate at anaphase I, yielding two types of daughter cells for this locus. 1 Each gamete gets one long chromosome with either the R or r allele. 2 Fertilization recombines the R and r alleles at random. 3 Alleles at both loci segregate in anaphase I, yielding four types of daughter cells depending on the chromosome arrangement at metaphase I. Compare the arrangement of the R and r alleles in the cells on

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