& Karyotypes The form of cell division by which gametes, with half the number of chromosomes, are produced. Homologous Chromosomes Pair of chromosomes (maternal and paternal) that are similar in shape, size, banding patterns and position of centromeres. --Because a homologous pair consists of 4 chromatids, eye color locus hair color locus it is called a Tetrad. eye color locus hair color locus Chromosomes Diploid number (2n) A cell that contains both sets of chromosomes. One set comes from the mother (and has the mother s DNA). The other comes from the father (and has the father s DNA). Most are diploid. Humans have 23 pairs of chromosomes. The diploid number for humans is 46. (46 chromosomes per cell.) Haploid number (1n) A cell that contains one set of chromosomes. The haploid number for humans is 23. Paternal Maternal
Humans have 23 Pairs of Homologous Chromosomes. This is a picture of them and is called a Karyotype. Autosomes Sex Chromosomes In humans Autosomes are pairs 1-22 Sex Chromosomes = the 23 rd pair This person has 2 X chromosomes and is a female. 23 The Sex Chromosomes code for the sex of the offspring. ** If the offspring has two X chromosomes it will be a female. ** If the offspring has one X chromosome and one Y chromosome it will be a male. Organisms that reproduce Sexually are made up of two different types of. 1. Somatic Cells = body contain the normal number of chromosomes Diploid (2n). Examples: skin, brain, etc. 2. Gametes = sex contain only ½ the normal number of chromosomes Haploid (n) Examples: Sperm and egg The male gamete is the sperm and is produced in the testes. The female gamete is the Ovum (ova = pl.) and is produced in the ovaries. XX chromosome - female XY chromosome - male
is the process by which gametes (sex ), with half the number of chromosomes, are produced. During diploid are reduced to haploid Diploid (2n) Haploid (n) If did not occur the chromosome number in each new generation would double. Diploid (2n) Haploid (1n) sperm egg (gametes) _ Fertilization _ Diploid cell (2n) Fertilized egg = Zygote is two cell divisions (called meiosis I and meiosis II) with only one duplication of chromosomes. Interphase I Similar to mitosis interphase. Chromosomes replicate (S phase). Each replicated chromosome consists of two identical sister chromatids attached at their centromeres. Nucleus and nucleolus visible. cell membrane chromatin nuclear membrane nucleolus I (four phases) Cell division that reduces the chromosome number by one-half. four phases: a. prophase I b. metaphase I c. anaphase I d. telophase I
Prophase I Chromosomes condense. Homologous chromosomes come together to form a tetrad. Crossing over can occur. Prophase I Homologous chromosomes Crossing Over During Crossing over segments of nonsister chromatids break and reattach to the other chromatid. creates variation (diversity) in the offspring s traits. sister chromatids Tetrad sister chromatids nonsister chromatids Crossing Over Tetrad spindle fiber Prophase I centrioles Metaphase I Tetrads align in the middle. INDEPENDENT ASSORTMENT OCCURS: 1. Orientation of homologous pair is random. 2. Variation 2 23 = 8,388,608 different combinations variation
Metaphase I Anaphase I Anaphase I OR Homologous chromosomes separate and move towards the poles. Sister chromatids remain attached at their centromeres. metaphase plate metaphase plate Telophase I Each pole now has haploid set of chromosomes. Telophase I cytokinesis II No Interphase II; II is similar to Cytokinesis occurs and two haploid daughter are formed. 2 haploid daughter
Prophase II same as Prophase in mitosis Spindles form Metaphase II Chromosomes line up in the middle Anaphase II Spindles pull sister chromatids apart metaphase plate metaphase plate Telophase II Telophase II Nuclear envelopes form. Cytokinesis occurs. REMEMBER: four genetically different haploid daughter produced. in males is called spermatogenesis and produces sperm. in females is called oogenesis and produces ova.
Spermatogenesis human sex cell Primary Spermatocyte 2n=46 diploid (2n) meiosis I Secondary Spermatocyte Secondary Spermatocyte meiosis II sperm haploid (n) Oogenesis *** The polar bodies die only one ovum (egg) is produced from each primary oocyte. Fertilization results in the formation of a Zygote (fertilized egg) n=2 3eg g Sperm + Ovum (egg) sper m fertilization 2n=4 6 zygot Zygote e Comparing and Comparing and Comparing and Produces Occurs in Produces Occurs in Produces 2 genetically identical. Occurs in Produces 4 genetically different. Occurs in Produces 2 genetically identical. Occurs in body (somatic) Produces 4 genetically different. Occurs in sex (gamete)
Comparing and Comparing and Non-disjunction Produces 2 genetically identical. Occurs in body (somatic) DNA replicates once, divides once. Produces 4 genetically different. Occurs in sex (gamete) DNA replicates once, divides twice. Produces 2 genetically identical Occurs in body (somatic) DNA replicates once, divides once No crossing over Produces 4 genetically different Occurs in sex (gamete) DNA replicates once, divides twice Crossing over can occur Non-disjunction = the failure of homologous chromosomes to separate during meiosis. Results in zygotes with abnormal chromosome numbers Common Non-disjunction Disorders Trisomy 21 Down s Syndrome Trisomy 21 Turner s Syndrome Monosomy 23 (X) Klinefelter s Syndrome Trisomy 23 (XXY) Edward s Syndrome Trisomy 18