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Chromosomes

Chromosomes

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Chromosomes

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  1. Chromosomes Packaged Instructions for Life

  2. Structure • Chromosomes are packages of DNA wrapped with help of proteins called histones • Composed of two identical sisterchromatidsattached at centromere

  3. Each sister chromatid contains thousands of identical genes in the same locations on each • Gene: segment of DNA that codes for specific proteins • Ex: hair color, eye color, lip shape, etc Gene A Gene B Gene C Gene D Gene E

  4. Each human somatic or body cell contains two copies of each chromosome • 23 sets of chromosomes x 2 = 46 total (other species differ in numbers) • Combination of all 23 is TOTAL DNA genome (3 billion base pairs)

  5. One set (23rd) contains sex chromosomes X and/or Y • Females have XX • Males have XY (Y is just shorter) Females: XX Males: XY

  6. Two sets of chromosomes = diploid (somatic cells) • One set of chromosomes = haploid (gametes) • Necessary since combination of chromosomes from egg & sperm must be diploid to produce viable (able to live) offspring • Fertilized egg = zygote = =

  7. Diploids have same gene (eye color) but may have different variations (brown vs. blue eyes) • called homologouschromatids (similar info) • One from mother, one from father gene for eye color (mom’s brown eyes) dad’s blue eyes

  8. Map of all 23 sets of chromosomes from a body/somatic cell is called a karyotype • Numbered from 1 – 23 based on length, location of centromere, and banding pattern

  9. Typical Karyotype w/ 23 Chromosome Pairs female male

  10. Karyotypes are usually only completed for cases where there might be a chromosomal abnormality • Monosomy (missing homolog) • Trisomy (Extra homolog) • Incorrect sex chromosome numbers

  11. Chromosomal abnormalities • Result of mistakes in gamete production (meiosis) • Each gamete (sperm & egg) is haploid • Duplication of gamete can result in accidents causing 2 or more sets of specific chromosome (rather than necessary 1 set)

  12. Down Syndrome • Trisomy 21 (3 #21 chromosomes) resulting in mental retardation • 1 in 1,300 at age 25 • 1 in 1,000 at age 30 • 1 in 400 at age 35 • 1 in 100 at age 40 • 1 in 35 at age 45

  13. He was born with an extra #21

  14. Edward Syndrome • Trisomy 18 (3 #18 chromosomes) resulting in medical complications that usually result in 50% stillbirths & high mortality rate in general • 1 in 5,000 births

  15. Patau Syndrome • Trisomy 13 (3 #13 chromosomes) resulting in cleft lip or palate, close-set eyes, severe mental retardation • 1 in 16,000 births

  16. Turner Syndrome • Females with monosomy (missing) X (also shown as XO) • 1 in 2,500 girls

  17. Triple-X Syndrome • Females with XXX (or XXXX or XXXXX) • No physical defects, some have learning disabilities, tall stature • 1 in 1,000 girls

  18. Klinefelter Syndrome • Males with XXY or XXXY • 1 in 1,000 boys • Low levels of testosterone, female-like features, infertile

  19. Jacobs or Super Male Syndrome • Males with XYY • 1 in 2000 • Mostly average, but excess acne, very tall, slightly increased aggression

  20. Chromosomal mutations • Breakage of entire chromosome, and sometimes reattachment can lead to four types of drastic mutations that may involve MANY genes: • Deletion • Duplication • Inversion • Translocation • Effects depend on number of genes involved and on which chromosome A B C D E A B C D E F G H F G H

  21. Deletion A B C D E A B E • Segment of chromosome gets deleted (missing genes) F G H F G H after before

  22. Deletion disorders • Cri-du-chat (cat cry) syndrome • deletion on chromosome 5 • children have a cat-like, high-pitched cry during infancy • mental retardation and physical abnormalities • About 1 in 20,000 to 50,000 babies is born with this disorder Allie Wallace, left, who is 5, and Katie Castillo, who is 20, both have "cri du chat" or cat cry syndrome, a rare genetic disorder that causes an array of mental and physical impairments.

  23. Prader-Willi syndrome • deletion on chromosome 15 • mental retardation or learning disabilities, behavioral problems and short stature • may develop extreme obesity • About 1 in 10,000 to 25,000 babies is affected.

  24. 22q11 deletion syndrome • Specific deletions on chromosome 22 • About 1 in 4,000 babies born • deletions cause a variety of problems that can include heart defects, cleft lip/palate, immune system abnormalities, characteristic facial features and learning disabilities • Certain combinations of these features are sometimes called DiGeorge or velocardiofacial syndrome. • Individuals with this disorder have a 50-percent chance of passing the chromosomal abnormality on to their offspring with each pregnancy.

  25. Wolf-Hirschhorn syndrome • deletion on chromosome 4 • characterized by mental retardation, heart defects, poor muscle tone, seizures and other problems • affects about 1 in 50,000 babies

  26. Duplication A B C D C D E A B C D E • Segment of chromosome gets attached to normal chromosome, duplicating certain genes F G H F G H before after

  27. Duplication disorders • Charcot-Marie-Tooth disease • Duplication on chromosome 17 • destroys muscle tissue and hinders the sense of touch • breaks down strong tissue and cripples the hands & feet • one of the most common inherited neurological disorders, with 36 in 100,000 affected The lack of muscle, high arch, and hammer toes are signs of the genetic disease.

  28. Inversion A B C D E A B D C E • Segment of chromosome gets broken off, then reattached upside down F G H F G H before after

  29. Inversion disorders • Norrie Disease • Causes blindness and oftentimes hearing loss • Some mental retardation • On X chromosome • All males affected • Females affected only if occurs on both X (otherwise are carriers)

  30. Translocation A B C D X Y E A B C D E • Segments of gene from one chromosome get broken off and reattached to a different chromosome F G H F G H before after

  31. Translocation disorders • Many common disorders • Infertility (13 to14) • Schizophrenia (1 to 11) • Certain leukemias (1 to 12; 17 to 15) • Certain sarcomas (11 to 22) • Certain lymphomas (11 to 14; 5 to 1; 8 to 14)