Ch 13_meiosis_post - Meiosis and Sexual Life Cycles....

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Meiosis and Sexual Life Cycles. Overview: Variations on a Theme Living organisms are distinguished by their ability to reproduce their own kind Genetics is the scientific study of heredity and variation Heredity is the transmission of traits from one generation to the next Variation is demonstrated by the differences in appearance that offspring show from parents and siblings
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Offspring acquire genes from parents by inheriting chromosomes In a literal sense, children do not inherit particular physical traits from their parents It is genes that are actually inherited
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Inheritance of Genes Genes are the units of heredity, and are made up of segments of DNA Genes are passed to the next generation through reproductive cells called gametes (sperm and eggs) Each gene has a specific location called a locus on a certain chromosome Most DNA is packaged into chromosomes One set of chromosomes is inherited from each parent
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Comparison of Asexual and Sexual Reproduction In asexual reproduction , one parent produces genetically identical offspring by mitosis A clone is a group of genetically identical individuals from the same parent In sexual reproduction , two parents give rise to offspring that have unique combinations of genes inherited from the two parents
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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 A life cycle starts at the conception of an organism and continues until the organism produces its own offspring.
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Sets of Chromosomes in Human Cells Human somatic cells (any cell other than a gamete) have 23 pairs of chromosomes 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 homologs Chromosomes in a homologous pair are the same length and carry genes controlling the same inherited characters
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The sex chromosomes are called X and Y Human females have a homologous pair of X chromosomes (XX) Human males have one X and one Y chromosome The 22 pairs of chromosomes that do not determine sex are called autosomes
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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 from the mother and one from the father A diploid cell (2 n ) has two sets of chromosomes For humans, the diploid number is 46 (2 n = 46) In the fruit fly, Drosophila , 2 n = 8 and n = 4. In the domestic dog, 2 n = 78 and n = 39.
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In a cell in which DNA synthesis has occurred, each chromosome is replicated Each replicated chromosome consists of two identical sister chromatids
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A gamete (sperm or egg) contains a single set of chromosomes, and is haploid ( n ) For humans, the haploid number is 23 ( n = 23) Each set of 23 consists of 22 autosomes and a single
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This note was uploaded on 04/30/2011 for the course BIOL 1362 taught by Professor Loeblich during the Spring '08 term at University of Houston.

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Ch 13_meiosis_post - Meiosis and Sexual Life Cycles....

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