Chromosomal Mutations Changes in Chromosome Number or Structure
Chromosomal Mutations Changes in Chromosome Number or Structure Alterations of Inheritance Patterns by Gender
Alterations in Chromosome Number • Polyploidy: one or more extra sets of chromosomes • Aneuploidy: gain or loss of one chromosome or a small number of chromosomes
Aneuploidy • Arises by Non-disjunction • Non-disjunction = failure of homologues or chromatids to separate during meiosis Normal Meiosis Non-disjunction in Meiosis II
Human Chromosomal Aneuploids Autosomal Aneuploids Down Syndrome Trisomy 21 Edward Syndrome Trisomy 18 Patau Syndrome Trisomy 13 Trisomy: three copies of one chromosome
Human Autosomal Abnormality Down Syndrome Trisomy 21 Three copies of chromosome 21 How can Down Syndrome occur? Eg. Egg with 2 copies of #21 (24 chromosomes) + Sperm with 1 copy of #21 (23 chromosomes) = Embryo with 3 copies of #21 (47 chromosomes)
Karyotype for Down Syndrome Physical Features Eye fold Palm Crease
Incidence of Down Syndrome Increases with Maternal Age Number per 1000 Births 400 300 200 100 0 10 20 30 40 50 Age of Mother (years)
Applying Your Knowledge 1. 2. 3. 4. 5. Polyploidy Non-disjunction Aneuploidy Crossing-over Trisomy A. Which one involves the loss of one chromosome? B. Which one describes the failure of chromatids to separate in Anaphase II? C. Which one involves the gain of an extra set of chromosomes? D. Which is the most specific description for the cause of Down Syndrome?
Human Chromosomal Aneuploids Sex Chromosome Aneuploids Turner Syndrome 45, XO Sterile female Triplo-X 47, XXX Fertile female Klinefelter Syndrome 47, XXY Sterile male XYY Syndrome Fertile male 47, XYY
Human Sex Chromosome Abnormality Turner Syndrome XO One copy of X No second sex chromosome How can Turner Syndrome occur? Eg. Egg with 0 copies of X (22 chromosomes) +Sperm with 1 copy of X (23 chromosomes) = Embryo with 1 copy of X (45 chromosomes)
Karyotype for Turner’s Syndrome
Chromosome Structure Changes Change Deletion Description Loss of a chromosomal segment Repeat of a chromosomal Duplication segment Translocation Movement of chromosomal segment to non-homologous chromosome Reversal of a chromosomal Inversion segment (rotated 180 o)
Chromosome Deletion in Humans Cri-du-chat syndrome is correlated with a deletion at the end of chromosome 5.
Chromosome Duplication in Humans Ø Small duplications in chromosome 15 cause no symptoms Ø Large duplication (with inversion) causes seizures and mental retardation
Ø Reciprocal Translocation involves exchange between two nonhomologous chromosomes Ø Reciprocal translocation between chromosomes 2 and 20 causes Alagille Syndrome Chromosome Translocation in Humans
Chromosome Translocation in Humans Ø Robertsonian Translocation involves a fusion of the long arms of two different chromosomes Ø Translocation Down Syndrome involves a Robertsonian Translocation between chromosomes 14 and 21
Applying Your Knowledge 1. 2. 3. 4. Deletion Duplication Inversion Translocation Which type of structure change a. represents an exchange between two non-homologous chromosomes? b. represents a reversal of a chromosome segment? c. represents a loss of a chromosomal segment?
Interaction between Gender and Heredity Sex-influenced characteristic Determined by autosomal genes Expression differs by gender Example: Pattern Baldness Caused by a dominant allele in males, but a recessive allele in females John Adams John Quincy Adams bb BB or Bb bb
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