Chapter 13 - Meiosis and Sexual Life Cycles

Chapter 13 - Meiosis and Sexual Life Cycles - Chapter 13...

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Chapter 13 Class Notes – Meiosis and Sexual Life Cycles – Page 1 Max Sauberman AP Biology – Mr. Schilp Chapter 13 Meiosis and Sexual Life Cycles Hereditary Similarity and Variation: Living organisms are distinguished by their ability to reproduce their own kind. Heredity is the transmission of traits between one generation to the next. Variation shows that offspring differ in appearance from parents and siblings. Genetics is the scientific study of heredity and variation. Inheritance: Offspring acquire genes from parents by inheriting chromosomes. In a literal sense, children do not inherit particular physical traits from their parents. They inherit genes from their parents. Inheritance of Genes: Genes are the units of heredity. Genes are segments of DNA. Each gene has a specific locus (location) on a certain chromosome. One set of chromosomes is inherited from each parent. Reproductive cells called gametes (sperm and egg) unite, passing genes to the next generation. Asexual vs. Sexual Reproduction: In asexual reproduction, one parent produces genetically identical offspring by mitosis. Budding is also an asexual process. In sexual reproduction, two parents give rise to offspring that have unique combinations of genes inherited from the two parents. The Sexual Life Cycle: Fertilization and meiosis alternate in sexual life cycles. A life cycle is the generation-to-generation sequence of stages in the reproductive history of an organism. Sets of Chromosomes in Human Cells:
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Chapter 13 Class Notes – Meiosis and Sexual Life Cycles – Page 2 Each human somatic cell (any cell other than a gamete) has 46 chromosomes arranged in pairs. A karyotype is an ordered display of the pairs of chromosomes from a cell. The two chromosomes in each pair are called homologous chromosomes, or homologues. Both chromosomes in the pair carry genes controlling the same inherited characteristics. Sex Chromosomes: The 23 rd pair of chromosomes is the sex chromosomes, which take the form of X or Y. Human females have a homologous pair of X chromosomes. Human males have one X and one Y chromosome. The 22 pairs of chromosomes that do not determine sex are called autosomes. Homologous Chromosomes: Each pair of homologous chromosomes includes one chromosome from each parent. The 46 chromosomes in a human somatic cell are two sets of 23: one set from each parent. The number of chromosomes in a single set is represented by n . The diploid number represents how many diploids ( homologous duplicated chromosomes) are in one cell. A cell with two sets is a diploid or 2n . For humans, the diploid number is 46, or in other words, 2n = 46 . In a cell where DNA synthesis has occurred, each chromosome is replicated ( 2n ).
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