GENETIC DISORDERS
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GENETIC DISORDERS. Mutation –change in a gene resulting in change in genetic information. may be spontaneous or caused by a mutagen Somatic mutations are usually not noticed Gametic mutations are more severe Not all mutations are bad !. SINGLE-GENE DEFECTS.

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GENETIC DISORDERS

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Genetic disorders

GENETIC DISORDERS


Mutation change in a gene resulting in change in genetic information

Mutation –change in a gene resulting in change in genetic information

  • may be spontaneousor caused by a mutagen

  • Somatic mutations are usually not noticed

  • Gametic mutations are more severe

  • Not all mutations are bad!


Single gene defects

SINGLE-GENE DEFECTS

  • Misplacement, insertion or deletion of one base pair

  • May result in incorrect amino acid

  • May result in shift of reading frame

  • Congenital Defects:

    • Visible at birth(club foot, spina bifida, congenital heart defects)

    • Caused by environmental factors (FAS, German measles)

  • Inherited

    • Sickle Cell Anemia, Cystic Fibrosis


Inversions

INVERSIONS

  • Part of chromosome is flipped around 180° from its normal orientation.

  • Happens when chromosome breaks occur.

  • Broken piece may reattach, but not necessarily in the same orientation as before


Translocations

TRANSLOCATIONS

  • Detachment of a segment of a chromosome, and reattachment to another non-homologous chromosome.

  • Some genes wind up on a completely different chromosome


Anomalies of chromosome number

ANOMALIES OF CHROMOSOME NUMBER

  • Polyploidy is common in plants

  • Gametes don’t reduce chromosome #

  • Result in cells with multiple copies of the genome


Anomalies of chromosome number1

ANOMALIES OF CHROMOSOME NUMBER

  • Aneuploidy – more common in humans

  • Usually lethal before or shortly after birth

  • Monosomic and Trisomic


Nondisjunction

NONDISJUNCTION

  • Occurs when homologous chromosomes fail to separate after synapsis

  • Most nondisjunction events are lethal to the fetus


Downs syndrome

DOWNS SYNDROME

  • Results from a third copy of chromosome 21

  • Called a trisomy

  • Individuals have 47 chromosomes in every body cell


Sex chromosome nondisjunction disorders

SEX CHROMOSOME NONDISJUNCTION DISORDERS

TURNER SYNDROME

  • Occurs when nondisjunction causes a gamete to have a missing sex chromosome (X O)

  • Sterile females

  • 1 in 10 000 live births


Sex chromosome nondisjunction disorders1

SEX CHROMOSOME NONDISJUNCTION DISORDERS

KLINEFELTER’S SYNDROME

  • Genotype of XXY (extra sex chromosome)

  • Sterile males, breast development

  • 1 in 800 live births


Sex chromosome nondisjunction disorders2

X

Y

O

XX

SEX CHROMOSOME NONDISJUNCTION DISORDERS

XY

XX


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