Transcript Chapter 6: Genetic diseases

CHAPTER 6:
GENETIC DISEASES
INTRODUCTION
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Cystic fibrosis:
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http://www.youtube.com/watch?v=Twjg7v-pTO4
WHAT ARE GENETIC DISEASES/DISORDERS?
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A genetic disorder is an illness caused by
abnormalities in genes or chromosomes
What are chromosomes?
CHROMOSOMES
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A normal human being has 46 of these
chromosomes in each cell (excepting reproductive
cells)
Of these 46 chromosomes, 44 are ‘autosomal’
 2 chromosomes are ‘sex chromosomes’
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X and Y
GENETIC DISORDERS
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Sometimes genetic disorders are caused by a
whole chromosome::
Down syndrome
 Klinefelter syndrome
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Down syndrome is caused by a trisomy:
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Instead of a pair of chromosomes, you have 3
In this case 21
 Down syndrome is also called ‘trisomy 23’.
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Other trisomies can occur, but often result in a
miscarriage
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For example: trisomy 16
TRISOMIES
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The most common types of autosomal trisomy
that survive to birth in humans are:
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Trisomy 21 (Down syndrome)
Trisomy 18 (Edwards syndrome)
Trisomy 13 (Patau syndrome)
Trisomy 9
Trisomy 8 (Warkany syndrome 2)
Trisomy 22
Sometimes, there is an extra copy of a sex
chromosome present:
XXX, XXY or XYY (XYY is not really a disorder)
 Klinefelter syndrome is an example: XXY
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GENETIC DISORDERS
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Other genetic disorders are not caused by a whole
chromosome, but by a fault in one or more genes
A gene is a molecular unit of heredity of a living
organism.
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It is a name given to some stretches of DNA and RNA
that code for a polypeptide or for an RNA chain that
has a function in the organism.
GENES
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http://www.youtube.com/watch?v=8s4he3wLgkM
Cystic fibrosis is an example of a disorder caused
by only 1 faulty gene
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You can only get it when this faulty gene is present
on both chromosomes of chromosome 7
If only one chromosome 7 has the faulty gene you
are a carrier
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You don’t get ill because the normal gene is dominant
over the faulty gene
CYSTIC FIBROSIS
HUNTINGTON’S DISEASE
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Cystic fibrosis is caused by a recessive (nondominant) gene
Some genetic disorders are caused by faulty
genes that are dominant
Huntington’s disease
 In this case you will get the disease, even if only one
copy of your chromosome 4 has the gene
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http://www.youtube.com/watch?v=4HgFUvVyHY
Q
WORK
Read pages 76 – 78
 Answer questions 1 - 6
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