CHAPTER 6:GENETIC DISEASES

INTRODUCTION

Cystic fibrosis:

http://www.youtube.com/watch?v=Twjg7v-pTO4

WHAT ARE GENETIC DISEASES/DISORDERS?

A genetic disorder is an illness caused by abnormalities in genes or chromosomes

What are chromosomes?

CHROMOSOMES

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’

X and Y

GENETIC DISORDERS Sometimes genetic disorders are caused by a

whole chromosome:: Down syndrome Klinefelter syndrome

Down syndrome is caused by a trisomy: Instead of a pair of chromosomes, you have 3

In this case 21 Down syndrome is also called ‘trisomy 23’.

Other trisomies can occur, but often result in a miscarriage For example: trisomy 16

TRISOMIES The most common types of autosomal

trisomy that survive to birth in humans are: 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

GENETIC DISORDERS

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. 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

http://www.youtube.com/watch?v=8s4he3wLgkM

Cystic fibrosis is an example of a disorder caused by only 1 faulty gene 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 You don’t get ill because the normal gene is

dominant over the faulty gene

CYSTIC FIBROSIS

HUNTINGTON’S DISEASE

Cystic fibrosis is caused by a recessive (non-dominant) 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

http://www.youtube.com/watch?v=4HgFUvVyHYQ

WORK

Read pages 76 – 78 Answer questions 1 - 6