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Transcript
Sexual Reproduction Meiosis Sexual Reproduction (Production of sperm cells and egg cells) Genes (a segment of DNA coding for specific traits) are located on chromosomes are carried from 2 parents (male and female) to offspring 1 chromosome from male,1 chromosome from female 1 complete set of information from each parent: (diploid-2n) 1 from male 1 from female A pair of chromosomes (carrying similar genetic information) Each colored =homologous chromosomes band is a gene (diploid-2n) Karyotyping are used to examine an individual’s chromosomes. Karyotypes are made from a sample of a person’s blood. Arranged from largest to smallest Last pair of chromosomes are The exception, they are sex chromosomes which determine the gender of the offspring XX = female, XY = male Meiosis: Cell division that halves the total number of chromosomes within the specie Ex. Frog has 8 half = 4, human has 46, half =23 Involves 2divisions of the nucleus # of chromosomes cut in half (haploid- n) homologous chromosomes are separated cell division similar to mitosis BUT 2x’s cells produced through meiosis are called gametes or sex cells, which contain only half,1/2, the hereditary information needed. Spermatogenesis oogenesis Sperm cells from the male contains ½ the hereditary info or 23 chromosomes Egg cells from the female contains ½ the hereditary info or 23 chromosomes Sperm + egg =fertilization 23 + 23 = 46 chromosomes A newly formed cell from 1 sperm cell and 1 egg cell is called a zygote Together, the organism has the correct number of chromosomes The resulting offspring is genetically different (variation) from the parents. Stages of Meiosis: Prophase I Interphase Chromosomes (DNA) replicate Prophase I Chromosomes pair up with other like chromosomes called homogulous pairs Homogulous pair pairing of homogulous chromosomes = synapsis This group of 4 chromatids (2 whole chromosomes) is called atetrad Chromosomes can exchange genetic informationcrossing over Metaphase I Tetrads line up in the middle Metaphase I Anaphase I Tetrad separate & move to opposite ends Chromosomes are still dbl. stranded Anaphase I Telophase I/ cytokinesis chromosomes reach the opposite ends of the cell, and cytokinesis begins 2 cells diploid (2n) Telophase I Prophase II centrioles separate centromeres attach to spindle fibers Prophase II Metaphase II Metaphase II chromosomes move to the middle Anaphase II centromere divides chromatids move to opposite ends chromosomes are haploid (n) Anaphase II Telophase II/cytokinesis 4 cells are formed ½ the genetic information nuclear membrane returns cytoplasm divides Nondisjunction, a common genetic disorder occurs when chromosomes do not separate properly during Anaphase I or Anaphase II. Meiotic Nondisjunction at Meiosis I Animation