HUMAN GENETICS

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HUMAN GENETICS
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HUMAN GENETICS

• 1. WHAT ARE SOME EXAMPLES IN HUMANS OF
  CHROMOSOMAL EFFECTS?
• 2. WHAT ARE SOME EXAMPLES IN HUMANS OF AUTOSOMAL
  DOMINANT AND RECESSIVE TRAITS?

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HUMAN GENETICS

• 3. WHAT ARE SOME OTHER FORMS OF INHERITANCE IN
  HUMANS?
• 4. WHAT IS A PEDIGREE?
• 5. HOW CAN GENETIC DISORDERS BE DETECTED?

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1. WHAT ARE SOME EXAMPLES IN HUMANS OF
CHROMOSOMAL EFFECTS?
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Chromosomal Inheritance

• All but one pair of chromosomes in males and
  females are the same.
• Autosomes - Nonsex chromosomes
• The different pair, sex chromosomes, determines
  the sex of an individual.
• X-linked (sex-linked) is the term used for genes
  carried on the X chromosome.

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X-Linked Alleles

• X-linked alleles have a different pattern of
  inheritance than alleles on autosomes because the
  Y chromosome is blank for these alleles.
• Inheritance of a Y chromosome cannot offset the
  inheritance of an X-linked recessive allele.

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Human X-Linked Disorders

• Color Blindness
• In humans, color vision receptors in the retina
  are three different classes of cone cells.
• Only one type of pigment is present in each class
  of cone cell.
• The allele for blue-sensitive is autosomal, but
  the red- and green-sensitive proteins are on the
  X chromosome.

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Human X-Linked Disorders

• Muscular Dystrophy
• Absence of protein dystrophin allows calcium to
  leak into muscle cells.
• Hemophilia
• Hemophilia A due to lack of clotting factor IX
  and hemophilia B due to lack of clotting factor
  VIII.

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Changes in Chromosome Number

• Monosomy and Trisomy
• Monosomy (2n - 1) occurs when an individual has
  only one of a particular type of chromosome.
• Trisomy (2n 1) occurs when an individual has
  three of a particular type of chromosome.

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Changes in Sex Chromosome Number

• An abnormal sex chromosome number is the result
  of inheriting too many or too few X or Y
  chromosomes.
• Nondisjunction during oogenesis or
  spermatogenesis.

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TURNER SYNDROME XO
KLINEFELTER XXY
TURNER SYNDROME X0
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Sex Chromosome Syndromes

• Poly-X Females
• More than two X chromosomes and extra Barr bodies
  in the nucleus.
• Range from tall and thin to tall and severely
  retarded depending on number of X chromosomes.
• Jacobs Syndrome
• XXY due to nondisjunction during spermatogenesis.
• Taller than average

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Changes in Chromosome Structure

• Deletion
• End of a chromosome breaks off, or two
  simultaneous breaks lead to loss of an internal
  segment.
• Translocation
• Movement of a chromosome segment from one
  chromosome to another, non-homologous chromosome.

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WILLIAMS SYNDROME
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ALAGILLE SYNDROME
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Changes in Chromosome Structure

• Duplication
• Presence of chromosomal segment more than once in
  the same chromosome.
• Known to occur as a result of an inversion in
  which segment is turned 180o.

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2. WHAT ARE SOME EXAMPLES IN HUMANS OF AUTOSOMAL
DOMINANT AND RECESSIVE TRAITS?
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Human Genetic Disorders

• Autosome - Any chromosome other than a sex
  chromosome.
• When a genetic disorder is autosomal dominant, an
  individual with AA or Aa has the disorder.
• When a genetic disorder is autosomal recessive,
  only aa individuals have the disorder.
• Carriers - Individuals unaffected by a disorder
  but can have an affected child.

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Human Genetic Disorders

• Autosome - Any chromosome other than a sex
  chromosome.
• When a genetic disorder is autosomal dominant, an
  individual with AA or Aa has the disorder.
• When a genetic disorder is autosomal recessive,
  only aa individuals have the disorder.
• Carriers - Individuals unaffected by a disorder
  but can have an affected child.

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Autosomal Recessive Disorders

• Tay-Sachs Disease
• Progressive deterioration of psychomotor
  functions.
• Cystic Fibrosis
• Mucus in bronchial tubes and pancreatic ducts is
  particularly thick and viscous.
• Phenylketonuria
• Lack enzyme for normal metabolism of
  phenylalanine.

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Autosomal Dominant Disorders

• Neurofibromatosis
• Tan or dark spots develop on skin and darken.
  Small, benign tumors may arise from fibrous nerve
  coverings.
• Huntington Disease
• Neurological disorder leading to progressive
  degeneration of brain cells, in turn causing
  severe muscle spasms and personality disorders.

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3. WHAT ARE SOME OTHER FORMS OF INHERITANCE IN
HUMANS?
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Multiple Allelic Traits

• When a trait is controlled by multiple alleles,
  the gene exists in several allelic forms.
• ABO blood types
• Phenotype Genotype
• A IAIA,IAi
• B IBIB,IBi
• AB IAIB
• O ii

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LARGE NUMBER OF TRIPLET REPEATS OF CGG AT FRAGILE
SITE ON X CHROMOSOME
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4. WHAT IS A PEDIGREE?
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5. HOW CAN GENETIC DISORDERS BE DETECTED?
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