Chromosomes

• •Coded information (“recipe”)
• for making proteins

•Genes are on our chromosomes

• Humans have 46 chromosomes or 23 pairs within
• a cell’s nucleus
• –Chromosome pairs 1 through 22 control traits that do not relate to gender of an individual.
• –The 23rd pair are the sex chromosomes that contain the genes that do control gender.
• •So most of the cells of our body have 23 pairs of chromosomes, or 46 total.
• •Only sperm and eggs have 1 of each pair or a
• total of 23 chromosomes.

• •Egg and Sperm
• –Gametes
• –For reproduction

• •All other cells
• –Have 23 pairs of
• chromosomes

• •Must make new cells for:
• –Repair
• –Growth
• •Do this by process of Mitosis
• (Duplication)
• •Creates two identical daughter cells

• •One of each chromosome (not pair)
• •Fuse together at fertilization
• •Produced by process of meiosis

•Produces cells with half the normal number of chromosomes

• •Egg and sperm fuse
• •Creates one cell with normal number of chromosomes
• •Cells replicate to form embryo

when the chromosomes line up in egg and sperm to separate they exchange some genes.

Chromosomes line up or "shuffle" randomly during Meiosis. •2^23, or 8 million possible assortments of chromosomes !

• Ovum has 8 million possible chromosome combinations, so does the sperm cell.
• 8 million x 8 million = 64 trillion
• possible combinations in EACH AND EVERY zygote

•Visual (snap shot) of one’s chromosomes

• •Normal Female: XX
• •Normal Male: XY

• •Growth and repair of cells
• •Occurs in body cells
• •1 division
• •Results in 2 daughter cells genetically identical cells (46chromosomes)

• •Formation of gametes
• •Occurs in sex cells
• •2 divisions
• •Results in 4 daughter genetically different cells (23
• chromosomes)

• •Nondisjunction occurs when both copies of a chromosome go into the same gamete (i.e. they fail
• to separate).
• •Results of nondisjunction:
• –Monosomy: cell has only 1 copy of a chromosome
• e.g. Turner syndrome (only one X chromosome)
• –Trisomy: cell has 3 copies of a chromosome
• e.g. Down syndrome (3 copies of chromosome 21)

• •Chromosomes occur in pairs (1 from each parent)
• •If missing one, usually fatal (except can have just one X)
• •If have more than 2 , usually fatal (except the smaller pairs of chromosomes ex. #21, or the sex chromosomes)

• •Extra copy of chromosome 21 from ova (advanced maternal age)
• •Short stature, eye shape, short fingers, rounded head, palm crease, mental retardation

• •One of the most common causes of mental retardation
• •Up to half of people with DS have heart defects
• •Up to 1/3 of people with DS have digestive disorders
• •Many have respiratory and immune system defects and increased chance for leukemia
• •Average life expectancy: 49 years of age

• •Screening blood tests in all pregnant womencan alert to increased chance of fetal down syndrome
• •Amniocentesis with karyotyping can detect Down Syndrome in utero

• •Poly-X female (XXX, XXXX)
• –XXX tends to be tall and thin but not usually retarded
• –XXXX are severely retarded
• •Jacobs syndrome
• (XYY) – tall, persistent acne, speech and reading problems

• Turner Syndrome (X) (females)
• •Immature sex organs, infertility, webbed neck, short stature, normal intelligence

• •1 in 650 males have XXY (instead of XY)
• •Often no signs •Sometimes becomes evident at puberty
• •Some characteristics:
• –Long legs, shorter trunk, less body/facial hair, enlarged teeth, enlarged breasts –Infertile
• –Symptoms vary from mild to severe
• –Can be given testosterone supplements

• •Chromosomes can be damaged, break, and not
• rejoin the way they should
• •Causes:
• –Radiation (remember Cherynobol & thyroid cancer)
• –Chemicals (ex. Cigarettes & lung cancer)
• –Viruses (sexually transmitted HPV and ovarian cancer)

• •Deletions: loss of a piece of the chromosome (e.g. Williams syndrome)
• •Translocations: movement of chromosome segments from one chromosome to different chromosome (Alagille
• syndrome)
• •Duplications: presence of a chromosome segment more than once in the same chromosome
• •Inversions: a segment of a chromosome is inverted 180 degrees

• •Deletion on chromosome 5- can be detected by Chorionic villus sampling
• •Causes varying levels of mental retardation
• •Characteristic “cry”
• –Abnormal larynx development
• •Scoliosis, muscle tone issues
• •Facial/skull abnormalities

• •Alagille Syndrome
• –Translocation between #2 & #20
• –Characteristic facial features: prominent forehead, small chin)
• –Abnormalities in eyes, internal organs (liver)
• –Can be mild or severe

• •Some kinds of cancer –
• –22 & 9
• myelogenous leukemia

• –8 & 14
• Burkett Lymphoma