1. HEREDITY AND INHERITED DISORDERS

2. CAN YOU READ THE NUMBERS?

3. HEREDITY AND SEX DETERMINATION:
Genetics is the study of how traits are passed from parent to child through genes and chromosomes
One pair of the 46 chromosomes is the sex chromosomes
Female gives X and X, Male gives X and Y, Male determines sex
If sperm Y joins with X from egg - male
If sperm X joins with X from egg - female

4. BACKGROUND: Genetic disorders can be caused by chromosomes or genes
Inherited disorders is caused by a gene passed from parent to child
Inherited disorders can be:
Dominant - a trait that will appear in the offspring if ONE parent donates it
Recessive - must be contributed by BOTH parents to appear in the offspring; recessive traits can be carried in a person’s genes without appearing in that person

5. What genes do you have?

6. Earlobe Variation
Whether a person is born with attached or detached earlobes depends on a single gene
Gene has two molecular forms (alleles)‏

7.                              
Earlobe Variation
You inherited one allele for this gene from each parent
Dominant allele specifies detached earlobes
Recessive allele specifies attached lobes
                             

8. Dominant & Recessive Alleles
If you have attached earlobes, you inherited two copies of the recessive allele (rr)‏
If you have detached earlobes, you may have either one or two copies of the dominant allele (RR or Rr)‏

9. Human Variation Some human traits occur as a few discrete types
Attached or detached earlobes
Many genetic disorders
Other traits show continuous variation
Height
Weight
Eye color

10. Do you know your genetics?
What is your phenotype?
What is your genotype?

11. Tongue roll or not? R r

12. Straight thumb or curly thumb?

13. H h

14. Widow's peak or not? W w

15. The PTC test:
Phenylthiocarbamide (PTC)/phenylthiourea (PTU), is a compound that has the unusual property that it either tastes very bitter or is virtually tasteless, depending on the genetic makeup of the taster. The genetic correlation was so strong that it was used in paternity tests before the advent of DNA matching.

16. What are you? Taster or not?
The PTC test continued
Ability to taste PTC is often treated as a dominant genetic trait, although inheritance and expression of this trait are somewhat more complex.
There are two common forms of the PTC gene; one is a tasting allele, and the other is a non-tasting allele.
Each codes for a bitter taste receptor protein with a slightly different shape.
shape of the receptor protein determines how strongly it can bind to PTC.
Approximately 70% of people are tasters.
What are you? Taster or not?

17. EXAMPLES OF RECESSIVE DISORDERS:
Sickle Cell Disease:
-Red blood cells have crescent shape
-Causes anemia and pain, most often in African Americans
Tay-Sachs Disease:
-Causes mental retardation, blindness, seizures, and death usually by age 5
-Most often seen in people of eastern European Jewish descent, French Canadians, and Cajuns
Cystic Fibrosis:
-Causes problems in digestion and breathing
-Most common fatal genetic disease in Canada
1 in 25 people are carriers of the gene for the disease

18. EXAMPLE OF DOMINANT DISORDER
Huntington’s Disease:
Dominant genetic disorder means each child of an affected parent has a 50% chance of inheriting the disorder
Neurodegenerative disorder that causes cells in the brain to die resulting in a loss of control of movement, emotions, recall events and make decisions
Death occurs years after the onset of symptoms
Huntington's Disease

19. X-LINKED/SEX-LINKED DISORDERS:
X-linked disorders are caused by genes on the X chromosome
Many more X-linked traits than Y-linked traits because the X chromosome is much larger than the Y chromosome
X-linked disorders are generally seen in males, why?
Males have only one X chromosome, therefore, no dominant gene to cancel out recessive gene

20. X-LINKED RECESSIVE DISORDERS:
These disorders are expressed in all males but only those females that have received both copies of the gene from their parents (ie. each of their X chromosomes carries the gene for the disorder)
All daughters of a female carrier have a 50% chance of becoming carriers
All daughters of an affected male will be carriers
All sons of an affected male will not carry the disease since they can only inherit Y from their father
Example: Duchenne muscular dystrophy:
Most often affecting males
Weakness, muscle wasting
Death by around 30

22. HAEMOPHILIA:
Inherited disorder that impairs the body’s ability to control blood clotting due to the absence of a specific clotting factor
Primarily seen in males
Also known as “The Royal Disease”
Queen Victoria passed gene onto son Leopold and daughters who then spread the gene into the Royal families in Spain, Russia and Germany
Most famous haemophiliac - Tsar Alexei's haemophilia was thought to contribute to the collapse of Imperial Russia during the Russian revolution due to his parents close ties with “healer” Rasputin, who later became a personal advisor to the Tsar’s wife (Alexandra)

23. X-LINKED DOMINANT DISORDERS:
Dominant gene for disorder is carried on the X chromosome
One copy of the gene will cause the disease
Less common than the X-linked recessive disorders
Example:
Fragile X Syndrome:
Most common cause of mental retardation
Piece of X chromosome is not fully attached