chromosomal mutations
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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 I
Non-disjunction in Meiosis II
Human Chromosomal Aneuploids
Down Syndrome Trisomy 21
Edward Syndrome Trisomy 18
Patau Syndrome Trisomy 13
Autosomal Aneuploids
Trisomy: three copies of one chromosome
Human Autosomal Abnormality
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)
Down Syndrome Trisomy 21
Three copies of chromosome 21
Karyotype for Down Syndrome
Eye fold Palm Crease
Physical Features
Incidence of Down Syndrome Increases with Maternal Age
10 20 30 40 500
100
200
300
400
Age of Mother (years)
Num
ber p
er 1
000
Birth
s
Applying Your Knowledge
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?
1. Polyploidy2. Non-
disjunction3. Aneuploidy4. Crossing-
over5. Trisomy
Human Chromosomal Aneuploids
Sex Chromosome Aneuploids
Turner Syndrome 45, XO
Triplo-X 47, XXX
Klinefelter Syndrome 47, XXY
XYY Syndrome 47, XYY
Sterile female
Fertile female
Sterile male
Fertile male
Human Sex Chromosome Abnormality Turner Syndrome XO
One copy of XNo 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 Description Deletion Loss of a chromosomal
segmentDuplication Repeat of a chromosomal
segment Translocation Movement of chromosomal
segment to non-homologous chromosome
Inversion Reversal of a chromosomal segment (rotated 180o)
Chromosome Deletion in Humans
Cri-du-chat syndromeis correlated witha deletion at the endof chromosome 5.
Chromosome Duplication in Humans
Small duplications in chromosome 15 cause no symptoms
Large duplication (with inversion) causes seizures and mental retardation
Chromosome Translocation
in Humans
Reciprocal Translocation involves exchange between two non-homologous chromosomes
Reciprocal translocation between chromosomes 2 and 20 causes Alagille Syndrome
Chromosome Translocation in Humans
Robertsonian Translocation involves a fusion of the long arms of two different chromosomes
Translocation Down Syndrome involves a Robertsonian Translocation between chromosomes 14 and 21
Applying Your Knowledge
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?
1. Deletion2. Duplication3. Inversion4. Translocation
Interaction between Gender and Heredity Sex-influenced characteristic
Determined by autosomal genesExpression differs by gender
bb
BB or Bb bb
BB or Bb
Example: Pattern BaldnessCaused by a dominant allele in males,
but a recessive allele in females
John Adams
John Quincy Adams
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