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Meiosis

Meiosis. Section 3.3. Vocabulary. Homologous chromosomes: Chromosomes that have the same sequence of genes and the same structure.

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Meiosis

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  1. Meiosis Section 3.3

  2. Vocabulary • Homologous chromosomes: Chromosomes that have the same sequence of genes and the same structure. • Meiosis: A process in cell division during which the number of chromosomes decreases to half the original number by two divisions of the nucleus, which results in the production of sex cells. • Sex chromosome: One of the pair of chromosomes that determine the sex of an individual. • Pedigree: A diagram that shows the occurrence of a genetic trait in several generations of a family.

  3. Asexual vs. Sexual Reproduction • In asexual reproduction, only one parent cell is needed. The structures inside the cell are copied and the parent cell divides into two identical cells. This is called MITOSIS. • In sexual reproduction, two parent cells join together to form offspring that are different from both parent cells. The parent cells are called sex cells. • Sex cells are different from ordinary body cells. • Human body cells have 46 chromosomes (or 23 homologous pairs). Sex cells only have 23 chromosomes.

  4. Genes & Chromosomes • A graduate student named Walter Sutton observed that cells’ chromosomes are located in the nucleus and proposed that genes are located on chromosomes.

  5. Meiosis & Mendel

  6. Sex Chromosomes • Sex chromosomes carry genes that determine sex. • In humans, females have two X chromosomes and males have one X and one Y chromosome. • During meiosis one of each of the chromosome pairs ends up in a sex cell. When meiosis produces egg cells, each egg contains one X chromosome. When meiosis produces sperm, they contain either an X or Y chromosome. An egg fertilized by a sperm with an X will be female and an egg fertilized by a sperm with a Y will be a male.

  7. Sex-Linked Disorders • Genes for certain disorders, such as colorblindness and hemophilia, are carried on the X chromosome. These disorders are called sex-linked disorders • Because the Y chromosome does not carry all the genes of an X chromosome and females have two X chromosomes (two copies of each gene), AND the gene for sex-linked disorders is recessive . . . men are more likely to have sex-linked disorders.

  8. Genetic Counseling • Genetic disorders can be traced through a family tree. Genetic counselors use a diagram, known as a pedigree, to predict whether a person is a carrier of a heredity disease.

  9. Selective Breeding • In selective breeding, organisms with desirable characteristics are mated. This is common in pets and plants.

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