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 *Sex chromosomes – represented differently in the 2 sexes - Females have a matched pair (XX) of sex chromosomes - Males do not have a matched pair (XY) of sex chromosomes

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 *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 length and centromere position are consistant for each chromosome

Chromosomes & Inheritance *Karyotypes are species specific *Human karyotype shows 46 chromosomes: autosomal (1-22) and sex (23) *They are numbered largest to smallest to help in identification *Chromosomes are arranged according to size and position of the centromere *They are also arranged together with similar morphologies (A-G)

Chromosomes & Inheritance

Shows some detail of the chromosomes. Can help determine the sex of an unborn child. Doctors look for some significant features o Check if the 46 chromosomes are present o Check the presence of the two identical chromosomes o Check the sex chromosomes o Check if there are any missing or rearranged chromosomes

Chromosomes & Inheritance Karyotypes do not show … The presence and location of small mutations. o So 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 *Chromosomal nomenclature, based upon banding pattern, has been established *Certain regions consistantly accept more staining than others, so chromosomal banding is specific

Chromosomes & Inheritance *The nomenclature is used to reference genes based upon regions of chromosomes *Numbered regions and subregions are then assigned from the centromere outward (1 is closest to the centromere) *Each chromosome has 2 arms separated by the centromere *The smaller arm is designated ‘p ‘ and the larger arm is desinated ‘q’

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 -It is located on chromosome 7, on the long arm and spans subregions 2 and 3 of 31 - Example: Cystic fibrosis gene is located at 7q31.2-q31.3

Chromosomes & Inheritance MITOSIS -cellular reproduction -cyclical -growth, mitosis (nuclear division), cytokinesis (cell division) Cell cycle -somatic cells: 2 main phases of cell cycle (1) M & (2) Interphase -Interphase -Interphase: G 1, S, G 2

Chromosomes & Inheritance INTERPHASE - G 1 – growth, preparation for chromosome replication -sister chromatids – 2 exact copies of each other, held together by a replicated, but unseparated centromere - S – replication of chromosomes - G 2 – preparation for cell division -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 -Prophase -Early Prophase – MITOSIS 1. Centrioles move apart 2. Chromosomes shorten, thicken & start to become visible 3. Nucleolus begins to disappear

Chromosomes & Inheritance -Prophase -Mid Prophase – MITOSIS 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 -Metaphase MITOSIS 1. Nuclear envelope is gone 2. Replicated chromosomes, attached at the centromere, align in the center (“equator”) 1. Centromeres split, daughter chromosomes migrate toward opposite sides -Anaphase -Early Anaphase –

Chromosomes & Inheritance MITOSIS 1. The 2 sets of daughter chromosomes approach the poles -Anaphase -Late Anaphase – 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

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