This chapter include objectives: Evaluate the effects of continuous variation, pleiotropic genes, lack of complete dominance, environmental modifications of genes, and epistasis on disease; understand the importance of crossing over in terms of gene assortment and construction of genetic maps; describe the many genetic disorders discussed in the text, their symptoms, relative frequency in specialized populations, and their genetic basis;. | Chromosomes, Mapping, and the Meiosis-Inheritance Connection Chapter 13 Chromosome Theory Chromosomal theory of inheritance - developed in 1902 by Walter Sutton - proposed that genes are present on chromosomes - based on observations that homologous chromosomes pair with each other during meiosis - supporting evidence was provided by work with fruit flies Chromosome Theory . Morgan isolated a mutant white-eyed Drosophila red-eyed female X white-eyed male gave a F1 generation of all red eyes Morgan concluded that red eyes are dominant Chromosome Theory Morgan crossed F1 females X F1 males F2 generation contained red and white- eyed flies but all white-eyed flies were male testcross of a F1 female with a white-eyed male showed the viability of white-eyed females Morgan concluded that the eye color gene is linked to the X chromosome Sex Chromosomes Sex determination in Drosophila is based on the number of X chromosomes 2 X chromosomes = female 1 X and 1 Y chromosome = male Sex determination in humans is based on the presence of a Y chromosome 2 X chromosomes = female having a Y chromosome (XY) = male Sex Chromosomes In many organisms, the Y chromosome is greatly reduced or inactive. genes on the X chromosome are present in only 1 copy in males sex-linked traits: controlled by genes present on the X chromosome Sex-linked traits show inheritance patterns different than those of genes on autosomes. Sex Chromosomes Dosage compensation ensures an equal expression of genes from the sex chromosomes even though females have 2 X chromosomes and males have only 1. In each female cell, 1 X chromosome is inactivated and is highly condensed into a Barr body. Females heterozygous for genes on the X chromosome are genetic mosaics. Chromosome Theory Exceptions Mitochondria and chloroplasts contain genes. traits controlled by these genes do not follow the chromosomal theory of inheritance genes from mitochondria and chloroplasts are often passed | Chromosomes, Mapping, and the Meiosis-Inheritance Connection Chapter 13 Chromosome Theory Chromosomal theory of inheritance - developed in 1902 by Walter Sutton - proposed that genes are present on chromosomes - based on observations that homologous chromosomes pair with each other during meiosis - supporting evidence was provided by work with fruit flies Chromosome Theory . Morgan isolated a mutant white-eyed Drosophila red-eyed female X white-eyed male gave a F1 generation of all red eyes Morgan concluded that red eyes are dominant Chromosome Theory Morgan crossed F1 females X F1 males F2 generation contained red and white- eyed flies but all white-eyed flies were male testcross of a F1 female with a white-eyed male showed the viability of white-eyed females Morgan concluded that the eye color gene is linked to the X chromosome Sex Chromosomes Sex determination in Drosophila is based on the number of X chromosomes 2 X chromosomes = female 1 X and 1 Y chromosome =
