1. Sex-Linked Traits and Chromosomal Disorders
EQ: Why do some people inherit certain traits?

2. Chromosomes
Sex Chromosomes- chromosomes that determine the sex of an organism
Autosomes- all other chromosomes
Both males and females can be carriers
Humans have 2 sex chromosomes X & Y and 44 autosomes

3. Karyotype
Can tell if the person is missing or have extra chromosomes as well as gender
Can’t see single gene mutations

4. Sex-linked traits
Sex chromosomes carry genes that are either on the X or Y chromosome
These traits show up in different percentages in males and females because they move with the sex chromosome

5. Y-linked genes Genes that are specifically carried on the Y chromosome
Y-linked genes ONLY show up in males
Example: Hairy ears

6. X-linked Genes Carried on the X chromosome
X-linked recessive disorders show up more frequently on males than females because males have only one X chromosome
Females can be carriers of recessive traits

7. Or Males ONLY HAVE ONE X They either have the They are disorder normal
DEFECTIVE
NORMAL
They either
have the
disorder
They are
normal Or

8. Females have one normal gene that works.
FEMALES HAVE TWO X CHROMOSOMES
DEFECTIVE
NORMAL
DEFECTIVE
Females have one normal gene that works.
Females __________ defective recessive
alleles to show the
disorder
need 2

9. Example of x-linked recessive disorders
Hemophilia
Cause: Mutations in genes for blood clotting proteins carried on X chromosomes
Blood clotting proteins are missing so a person with this disorder can’t stop bleeding when injured
Can bleed to death from minor cuts or suffer internal bleeding from bruises or bumps
Treatment: Injections of normal clotting proteins to stop bleeding
More common in males because it is X-linked, but females with 2 recessive alleles will also show the traits
1 in 10,000 males have hemophilia

10. Examples of x-linked recessive disorders
Color Blindness
Cause: Mutation in one of three genes for color vision carried on X chromosome
People with this disorder have trouble distinguishing colors
Red-Green colorblindness is the most common
Seen in 1 in 10 males and 1 in 100 females

11. Chromosomal Disorders
1 infant in 200 newborns has a chromosomal disorder
28% of first trimester miscarriages have a severe chromosomal abnormality
Chromosomal mutations- change in the structure or number of chromosomes

12. Nondisjunction
During Anaphase, the homologous chromosomes fail to separate during meiosis.
Since it happens to a sperm or egg cell, the new baby can end up with trisomy (3 copies) or monosomy (one copy) of the chromosome.

13. Nondisjunction

14. Example of Chromosomal Disorders
Down Syndrome
Cause: three copies of the 21st chromosomes
Most common chromosomal disorder (1 in 800 births)
50% have heart defects that need surgery to repair
Mild to severe mental deficiencies
Increase chances of having other diseases

15. Down Syndrome