BME 80H Lecture Notes - Lecture 20: Cri Du Chat, Xyy Syndrome, Aneuploidy
11 Jun 2018
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20th lecture
Klinefelter Syndrome (47, XXY) (figure 6.22)
- Extra sex chromosome, present in 1/1,000 male births
- XXY sometimes have intellectual impairment
- XXXY, XXXXY, etc. have increased impairment with each extra X
XYY Syndrome (47, XYY) (figure 6.23)
- Taller than average
- Normal fertility
c) Conclusions (figure 6.27)
- Must have an X chromosome to be viable
- Most aneuploidies do not survive to birth
II. Aberrations of Chromosome Structure
Often involves breaking and rejoining of chromosome parts. Occurs
in 1/400 live births
Causes of breaks: replication or recombination errors,
environmental agents
- Some viruses, some chemicals, radiation, X-rays
Types of aberrations: (fig. 6.24)
- deletion = chromosomal segment lost
- inversion = segment put into reverse orientation
(doesn't change amount of DNA, just the order)
- duplication = segment duplicated
find more resources at oneclass.com
find more resources at oneclass.com
- translocation = nonhomologous chromosomes swap
segments
A. Deletion: loss of a part of a chromosome (Handout cont.,
table 6.3)
Cri du chat syndrome: 46, del (5p) (figure 6.25).
- 2 phenotypes, cat like cry from larynx development and
mental impairment
- The 2 phenotypes result from different parts of 5p being
deleted
Prader-Willi Syndrome 46, del (15q) (figure 11.21/11.22)
- Deletion in part of long arm in chromosome 15
- 15q11-13 so bands 1-3 region 1 on the long arm of
chromosome 15
- Phenotype is insatiable appetite
- Eat to a point where it kills them
- Only occurs when the deletion is in the paternally provided
chromosome
- Genomic imprinting
- Example of epigenetics, but this occurs during meiosis
- Spermatogenesis and Oogenesis
- Imprinted (turned off) during oogenesis and not in
spermatogenesis (remain active)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Extra sex chromosome, present in 1/1,000 male births. Xxxy, xxxxy, etc. have increased impairment with each extra x. Must have an x chromosome to be viable. Most aneuploidies do not survive to birth. Often involves breaking and rejoining of chromosome parts. Causes of breaks: replication or recombination errors, environmental agents. Inversion = segment put into reverse orientation (doesn"t change amount of dna, just the order) Translocation = nonhomologous chromosomes swap segments table 6. 3: deletion: loss of a part of a chromosome (handout cont. , Cri du chat syndrome: 46, del (5p) (figure 6. 25). 2 phenotypes, cat like cry from larynx development and mental impairment. The 2 phenotypes result from different parts of 5p being deleted. Deletion in part of long arm in chromosome 15. 15q11-13 so bands 1-3 region 1 on the long arm of chromosome 15. Eat to a point where it kills them. Only occurs when the deletion is in the paternally provided chromosome.
