1. Genetic Diseases

2. Sex-linked Genes
Sex linked genes: genes located on the sex chromosomes
Many sex linked genes are found on the X chromosome
The Y chromosomes is much smaller than the X chromosome and appears to contain only a few genes

3. Color Blindness Why the difference?
3 human genes associated with color vision are located on the X chromosome:
In males, a defective version of any one of these genes produces color blindness
The most common form of color blindness is red green color blindness:
Male: 1 in 10
Female: 1 in 100
Why the difference?

4. More Colorblind Males than Females
It is sex-linked: genetic red–green color blindness affects males more because the genes for the red and green color receptors are located on the X chromosome
Sex Chromosomes: Males XY, Females XX
In, females (2 X chromosomes) a defect in one is typically compensated for by the other, while males only have one X chromosome.
Color blindness can also result from physical or chemical damage to the eye, optic nerve, or parts of the brain

5. Color Blindness Tests

6. What People With Regular Vision See

7. What Red-Green Color Blind People See

8. Cones Cones- (cone cells) are one of three types of
photoreceptor cells in the
retina of the eye that
provides color
vision and sharp
central vision.
They perceive short,
medium, & long
wavelengths which
translate to different
colors.

9. Types of Colorblindness
Tritanopia: Blue-Yellow Color Blindness, rare, autosomal chromosome 7 disorder, not sex linked
the short-cones are completely missing,
On the right side you see the tritan counterpart where you can spot how blue-yellow color blindness influences the view of colors.

10. Types of Colorblindness
Deuteranopia: Red-Green Color Blindness part 1 (number examples we saw earlier) sex linked
the medium-cones are missing, less able to see green

11. Types of Colorblindness
Protanopia: red-green colorblindness part 2,
(number examples we saw earlier) sex linked
the long-cones are completely missing, less able to see red

12. Red Green Color Blindness Inheritance
Males have just 1 X chromosome, so all X-linked alleles are expressed in males, even if there is only one recessive allele
Females have 2 X chromosomes, so there must be two copies of the recessive alleles present in order to express that allele

13. Red Green Color Blindness Inheritance
Males have just 1 X chromosome, so all X-linked alleles are expressed in males, even if there is only one recessive allele
Females have 2 X chromosomes, so there must be two copies of the recessive alleles present in order to express that allele
XBXB
XBXb
XbY
XBY
25%
25%
25%
25%
50%
normal children male & female

14. Hemophilia
Hemophilia is another example of a sex-linked (X linked) disorder: a protein necessary for normal blood clotting is missing
1 in 10,000 males born with a form of hemophilia
Hemophilia can be treated by injections of normal clotting
proteins. Without treatment, hemophiliacs will die before adulthood.

15. Duchenne Muscular Dystrophy
Duchenne Muscular Dystrophy is a sex-linked disorder that results in the progressive weakening and loss of skeletal muscle:
In the U.S, 1 in 3000 males are born with this disease
People with this disease rarely live past early adulthood

16. Chromosomal Disorders
Nondisjunction: Homologous chromosomes fail to separate
If nondisjunction occurs, abnormal numbers of chromosomes may find their way into gametes and a disorder of chromosomes numbers may result

17. Down Syndrome (Trisomy 21)
It is a form of trisomy- 3 copies of chromosome 21
Involves developmental abnormalities, low muscle tone, a slightly flattened facial profile and an upward slant to the eyes
1 in 700 is born with down syndrome

18. Sex Chromosome Disorders
Disorders that occur among the sex chromosomes:
Klinefelter’s syndrome: A male inherits more than one X chromosome (genotype XXY or XXXY)

19. Sex Chromosome Disorders
Disorders that occur among the sex chromosomes:
Turner’s syndrome: A female inherits only one X chromosome ( genotype XO)

20. What Disorder is this? How do you know?