Biology Meiosis and Mitosis

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AP Biology: Chapter 13 - Meiosis and Sexual Life Cycles

Overview
* The transmission of traits from one generation to the next is called inheritance, or heredity * Along with inherited similarity there is also variation * Genetics is the scientific study of heredity and hereditary variation I. 13.1 Offspring Acquire Genes from Parents By Inheriting Chromosomes A. Inheritance of Genes

* Parents endow their offspring with coded information in the form of hereditary units called genes * Most genes program cells to synthesize specific enzymes and other proteis, whose cumulative action produces an organism's inherited traits * In animals and plants, reproductive cells called gametes are the vehicles that transmit genes from one generation to the next * A gene's specific location along the length of a chromosome is called the gene's locus B. Comparison of Asexual and Sexual Reproduction

* In asexual reproduction, a single individual is the sole parent and passes copies of all its genes to its offspring without the fusion of gametes * An individual that reproduces asexually gives rise to a clone, a group of genetically identical individuals * In sexual reproduction, two parents give rise to offspring that have unique combinations of genes inherited from the two parents II. 13.2 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, from conception to production of its own offspring C. Sets of Chromosomes in Human Cells

* In humans each somatic cell has 46 chromosomes
* Karyotype is a display of the chromosomes pairs of a cell arranged by size and shape * Two chromosomes composing a pair have the same length, centromere position and staining pattern, these are called homologous chromosomes * The X and Y chromosomes are called the sex chromosomes

* Other chromosomes are called autosomes
* Any cell with two chromosomes sets is called a diploid cell and has a diploid number of chromosomes * Unlike somatic cells, gametes contain a single set of chromosomes, called haploid cells * Each sexually reproducing species has a characteristic diploid number and haploid number D. Behavior of Chromosome Sets in the Human Life Cycle

* A union of gametes, culminating in fusion of their nuclei is called fertilization * The resulting fertilized egg, or zygote, is diploid because it contains two haploid sets of chromosomes bearing genes representing the maternal and paternal family lines. * Only cells of the human body not produced by mitosis are the gametes, which develop from specialized cells called germ cells in the gonads * Sexually producing organisms, gamete formation involved meiosis E. The Variety of Sexual Life Cycles

* In the type that occurs in humans and most other animals, gametes are the only haploid cells. Meiosis occurs in germ cells during the production gametes, which undergo no further cell division prior to fertilization, after fertilization, the diploid zygote divides by mitosis, producing a multicellular organism that is diploid * Plants and some species of algae exhibit a second type of life cycle called alternation of generations. This type includes both diploid and haploid stages that are multicellular. The multicellular diploid stage is called the sporophyte. Meiosis in the sporophyte produced haploid cells called spores. Unlike a gamete a haploid spore does not fuse with another cell but divides mitotically generating a multicellular haploid stage called the gametophyte. Cells of the gametophyte give rise to gametes by mitosis. * Third type of life cycle occurs in most fungi and some protists, including some algae. After gametes fuse and form a diploid zygote, meiosis occurs without a multicellular diploid offspring developing. Meiosis produces not gametes but haploid cells that then divide by...
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