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Unformatted text preview: Chapter 13 (& 15: pp. 285-288): Cell Division by Meiosis and Genetic Disorders Terminology Heredity: The transmission of traits from one generation to the next. Genetics: The scientific study of heredity and hereditary variation. Chromosomes: tightly coiled DNA strands within the nucleus of each cell that contain instructions for the synthesis of thousands of different proteins (and other cell chemicals); there are 46 chromosomes in each human body (somatic) cell Karyotype: a photograph of the complete set of human chromosomes, displayed as homologous pairs of chromosomes Homologous pairs: The 46 chromosomes in each of our cells occur as 23 homologous pairs of chromosomes (homologues). 23 chromosomes come from our mother’s egg and 23 chromosomes come from our father’s sperm. Each of the two chromosomes that make up a homologous pair look alike (in terms of length and centromere location) and each contains the same kinds of genes (i.e., genes that code for the same traits). Sex chromosomes: Of the 23 homologous pairs of chromosomes, one pair (called the sex chromosomes) determines an individual’s gender. Sex chromosomes are designated as either X or Y. An individual with a genotype of XX is a female. An individual with a genotype of XY is a male. (NOTE: A pair of sex chromosomes made up of an X and a Y chromosome is not truly “homologous.” Can you explain why?) Autosomes: Excluding the sex chromosomes, the other 22 pairs of homologous chromosomes are called autosomes because they contain genes that code for body traits (som = body) other than gender. Diploid: The diploid number (2n) refers to the total number of chromosomes in each body (somatic) cell of any organism. In humans, the diploid number is 46 chromosomes. (The diploid number is different in each species of organism and can be used in species identification.) Haploid: The haploid number (n) refers to the number of chromosomes in each gamete (sperm or ova) produced by an organism. In human gametes the haploid number is 23 chromosomes. During MEIOSIS, the diploid number of chromosomes (in spermatogonia cells and oogonia cells) is reduced to the haploid number resulting in gametes (spermatozoa or ova). The process of producing gametes (by meiosis) is called gametogenesis. Gametogenesis in a male is called spermatogenesis. Gametogenesis in a female is called oogenesis. When a sperm and ovum (oocyte) unite during fertilization, the nuclei fuse and the zygote produced contains, once again, the diploid number of chromosomes. Meiosis insures that each new generation will have the same the zygote produced contains, once again, the diploid number of chromosomes....
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This note was uploaded on 04/07/2008 for the course BIO 101 taught by Professor Stein during the Spring '07 term at South Carolina.
- Spring '07