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Chromosomes & Inheritance Chromosomes – linear, double stranded *Number is specific to each species *Most eukaryotes have 2 copies of each -diploid *Gametes have only one set of chromosomes -haploid *Diploid organisms have homologous chromosomes – pairs that contain the same genes Chromosomes & Inheritance *Each member of the pair is called a homolog – 1 inherited from each parent *Chromosomes that contain different genes & do not pair in meiosis are nonhomologous *Sex chromosomes – represented differently in the 2 sexes - Females have a matched pair (XX) of sex chromosomes - homologous - Males do not have a matched pair (XY) of sex chromosomes - nonhomologous Chromosomes & Inheritance *Chromosomes other than the sex chromosomes are called autosomes *Chromosomes differ in size and appearance (morphology) within and between species *The point at which a chromosome is constricted (pinched) is called the centromere *The position of the centromere is used to classify eukaryotic chromosomes Chromosomes & Inheritance - Metacentric chromosome – centromere is in the center - Submetacentric chromosome – one arm is longer than the other - Acrocentric chromosome – one arm and a bulb - Telocentric chromosome – centromere is on the end Chromosomes & Inheritance *Chromosomes also vary in size *Chromosomes length and centromere position are consistant for each chromosome *A complete set of all the chromosomes in a cell is a karyotype (two chromatids per chromosome) - chromosomes from metaphase are used since they are the most compact and easily seen Chromosomes & Inheritance *Karyotypes are species specific *Chromosomes are arranged according to size and position of the centromere *Human karyotype shows 46 chromosomes: autosomal (1-22) and sex (23) *They are numbered largest to smallest to help in identification *They are also arranged together with similar morphologies (A-G) Chromosomes & Inheritance Chromosomes & Inheritance •Shows some detail of the chromosomes. •Can help determine the sex of an unborn child. •Doctors look for some significant features oCheck if the 46 chromosomes are present oCheck the presence of the two identical chromosomes oCheck the sex chromosomes oCheck if there are any missing or rearranged chromosomes Chromosomes & Inheritance Karyotypes do not show … •The presence and location of small mutations. oSo if diseases are caused by small mutations they cannot be predicted •Individual DNA strands or genes •The number of genes in any given area of a chromosome Chromosomes & Inheritance *Size and morphology are not enough to complete a karyotype *There are staining procedures used to “band” regions of the chromosomes *Certain regions consistantly accept more staining than others, so chromosomal banding is specific *Chromosomal nomenclature, based upon banding pattern, has been established Chromosomes & Inheritance *The nomenclature is used to reference genes based upon regions of chromosomes *Each chromosome has 2 arms separated by the centromere *The smaller arm is designated ‘p ‘ and the larger arm is desinated ‘q’ *Numbered regions and subregions are then assigned from the centromere outward (1 is closest to the centromere) Chromosomes & Inheritance - Example: Breast cancer susceptibility gene is located at 17q21 -What does this mean? -It is located on chromosome 17, on the long arm in region 21 -Subregions are then indicated with decimals after the region Chromosomes & Inheritance - Example: Cystic fibrosis gene is located at 7q31.2-q31.3 -It is located on chromosome 7, on the long arm and spans subregions 2 and 3 of 31 Chromosomes & Inheritance MITOSIS -cellular reproduction -cyclical Cell -growth, mitosis (nuclear division), cycle cytokinesis (cell division) -somatic cells: 2 main phases of cell cycle (1) M & (2) Interphase -Interphase -Interphase: G1, S, G2 Chromosomes & Inheritance INTERPHASE - G1 – growth, preparation for chromosome replication - S – replication of chromosomes - G2 – preparation for cell division -sister chromatids – 2 exact copies of each other, held together by a replicated, but unseparated centromere -chromatids – one of the two subunits of a replicated chromosome Chromosomes & Inheritance INTERPHASE - daughter chromosome – separted sister chromatids Chromosomes & Inheritance INTERPHASE - daughter chromosome – separated sister chromatids MITOSIS -Prophase -Early Prophase – 1. Centrioles move apart 2. Chromosomes shorten, thicken & start to become visible 3. Nucleolus begins to disappear Chromosomes & Inheritance MITOSIS -Prophase -Mid Prophase – 1. Centrioles continue to move 2. Spindles begin forming 3. Replicated chromosomes become visible -Late Prophase – 1. Centrioles reach opposite sides 2. Spindle continues to form 3. Nuclear envelope begins to disappear Chromosomes & Inheritance MITOSIS -Metaphase 1. Nuclear envelope is gone 2. Replicated chromosomes, attached at the centromere, align in the center (“equator”) -Anaphase -Early Anaphase – 1. Centromeres split, daughter chromosomes migrate toward opposite sides Chromosomes & Inheritance MITOSIS -Anaphase -Late Anaphase – 1. The 2 sets of daughter chromosomes approach the poles 2. Cytokinesis begins Chromosomes & Inheritance MITOSIS -Telophase 1. Nuclear envelope begins forming 2. Chromosomes begin to extend, less visible 3. Nucleolus reforms 4. Cytokinesis continues PowerPoint® Layered Art