1. Sex Linked Inheritance

2. Wait…. What????? What’s a “mosaic”?
Remember the FLUID MOSAIC MODEL????
The Plasma Membrane
P.S. What is a Plasma Membrane?
An individual (organism, artwork, organelle) made up of smaller, different ”pieces”…
So, in a way, WE ARE MOSAICS, too!

3. Calico Cats
Calico Cats can ONLY BE Female!

4. Why????
Because a cat’s fur color is linked to two different alleles on the “X” chromosome
And…For a cat to have more than two colors…
It must have TWO X CHROMOSOMES!

5. Sex-Linked Inheritance
Sex-Linked Inheritance means that a gene (or multiple genes) are carried on one of the sex chromosomes

6. Sex-Linked Inheritance
Remember, Females have XX and Males are XY.
The Y has very few genes - mainly those that contribute to male characteristics. (Only about 87 genes total.)
The X much more genetic information – for gender and other characteristics. (About 2050 genes!)

7. Sex-Linked Inheritance
Some genes for a disorder/disease are located on one of the sex chromosomes
If the gene is linked to the “Y” chromosome, women will not have the disorder.
Why? _________________________________
If the gene is linked to the “X” chromosome, and it is recessive, women will not express the disorder.
Why? ______________________________________
If the gene on “X” is dominant… both will express it!

8. Who is usually affected by Sex-Linked Disorders?
MEN! Genes for certain traits are on the X chromosome only…
Since Men only have one X chromosome then they are more likely to have the disorder
Women are somewhat protected since they have two X chromosomes and are less likely to inherit receive disorders.
If women receive a recessive gene on one X chromosome, they are called “carriers” because they “carry” the gene but don’t express the disorder

9. Sex-Linked Disorders
Affected males never pass the disease to their sons
Men give their “Y” to their sons!
Affected males pass the defective X chromosome to all of their daughters, who are described as carriers
This means they carry the disease-causing allele but generally show no symptoms
Female carriers pass the defective X chromosome to…
half their sons (affected by the disease)
half their daughters (who are carriers)
The other children inherit the normal copy of the chromosome

10. How do you solve Sex-linked Problems?
If Red eyes are dominant and sex-linked, show the cross between a homozygous red eyed female and a white eyed male.
You determine which trait (or disorder) is dominant or recessive
Set up a punnett square using XX for females and XY for males.
Assign alleles for X only!
Solve as usual, keeping in mind that the Y chromosome has no allele!
Genotypes: XRXr , XRY
Phenotypes: All offspring have red eyes.

11. Your Turn!
Hemophilia is a sex-linked trait where XH gives normal blood clotting and is dominant to the hemophilia allele Xh
Identify the genotypes of…
1) a woman with normal blood clotting whose father had hemophilia
2) a normal man whose father had hemophilia.
What is the probability that a mating between these two individuals will produce a child, regardless of sex, that has hemophilia?

12. Set up the Punnett Square!
- a woman with normal blood clotting whose father had hemophilia  XHXh - a normal man whose father had hemophilia  XHY Genotypes: Phenotypes:

13. What are some X-linked disorders?
ALD
Hypertrichosis
Duchenne muscular dystrophy
Hunter Syndrome
Menkes disease(kinky hair syndrome)
Hemophilia
Color blindness
Inherited diabetes (Type 1)

14. ALD (Adrenoleukodystrophy)
A deadly genetic disease that is a result of fatty acid buildup caused by the enzymes not functioning properly
Causes damage to the nerves, resulting in neurological issues and, later, death

15. Hypertrichosis An abnormal amount of hair growth over the body
Informally called werewolf syndrome, because the appearance is similar to the mythical werewolf

16. Hypertrichosis

17. Are you colorblind?

18. Color Blindness
Having a decreased ability to see some colors or differences in colors
Red-Green is most common

19. Think how difficult some things would be if you have colorblindness

20. What about this….
Imagine life without being able to see true colors!

21. Menke’s Disease (Kinky Hair Syndrome)
Rapid deterioration of the nervous system.
Weak muscle tone, sagging facial features, seizures, developmental delay, and intellectual disability caused by enzymes not functioning
Children with Menkes syndrome typically begin to develop symptoms during infancy and often do not live past age 6 

22. Menke’s Disease

23. Hemophilia
The “Royal Blood Disease” impairs the body's ability to make blood clots
Clots are needed to stop bleeding
This results in people bleeding longer after an injury and an increased risk of bleeding inside joints or the brain

24. Hemophilia
Remember the Royal Family?

25. Tay-Sachs
Tay-Sachs disease is a rare inherited disorder that progressively destroys nerve cells (neurons) in the brain and spine
Enzymes are the culprit AGAIN!
Paralysis of the nerves cause eventual death

26. Tay-Sachs
Tay Sachs

27. Duchene Muscular Dystrophy
Duchenne muscular dystrophy (DMD) is a genetic disorder characterized by progressive muscle degeneration and weakness
Until relatively recently, boys with DMD usually did not survive much beyond their teen years
Advances in cardiac and respiratory care means that survival into the early 30s is becoming more common

28. Duchenne Muscular Dystrophy

29. PKU (PhenylKetonUrea)
Decreased metabolism of the amino acid phenylalanine
Enzymes can’t break it down!
Untreated PKU can lead to intellectual disability, seizures and death 

30. PKU

31. Cystic Fibrosis (CF)
A genetic disorder that affects mostly the lungs, but also the pancreas, liver, kidneys, and intestine Cystic Fibrosis
The enzymes required to break down mucous are not functioning, so the mucous collects and clogs…

32. SCID (Severe combined immunodeficiency)
Do you know “David, the Boy in the Bubble”, who was born without a working immune system?

33. SCID What happens when your immune system doesn’t work???

34. Albinism
Albinism is an inherited genetic condition that reduces the amount of melanin pigment formed in the skin, hair and/or eyes. Albinism occurs in all racial and ethnic groups throughout the world.
As well as other species!

35. Albino Animals

36. Different degrees of Albinism…

37. Y linked
Hairy ears