1. Chromosomes & Phenotype Genetic Disorders
The Human Genome
Chromosomes & Phenotype Genetic Disorders

2. Autosomal vs Sex Linked Traits
Autosomes
All the chromosomes that do NOT play a role in sex determination
In humans, chromosomes 1 – 22
Two copies
One from Mom
One from Dad
Same genes
Same location on chromosome
BUT may be different alleles (recipes)

3. Autosomal vs Sex Linked Traits
Sex Linked Genes
Genes on the X or Y chromosome
X Chromosome
Large
Contains many genes, some essential for survival
Y Chromosome
Small
Few genes except those necessary to change fetal development from female to male

4. Autosomal Disorders caused by Recessive Alleles
Recessive Alleles cause disorder
Heterozygotes are Carriers
Can pass damaged allele to offspring BUT don’t have the disease/disorder
Homozygous Recessive individuals have the disease/disorder

5. Autosomal Disorders caused by Recessive Alleles
Cystic Fibrosis
Mutation of CFTR gene on chromosome 7
Causes thick mucus in lungs & blockage of gastrointestinal tract
Damages the pancreas
Fatal
Both parents must be heterozygous to have a child with the disease

6. Autosomal Disorders caused by Dominant Alleles
Dominant allele disorders far less common
Huntington’s Disease
Mutation of HTT gene on chromosome 4
Appears during adulthood – usually yrs. old
Allow time for person with disease to reproduce
Nervous system disintegrates slowly over years
Fatal

7. Autosomal Disorders caused by Dominant Alleles
Neurofibromatosis
Autosomal Dominant Disorder
Chromosome 22

8. Sex-Linked Genes
Sex Linked Genes Are Genes Located On The X & Y Chromosome X – Contains > 100 Genes Y – Contains Only A Few Genes

9. Sex-Linked Genes

10. The X Chromosome Contains Three (3) Genes Associated With Color Vision
Colorblindness
The X Chromosome Contains Three (3) Genes Associated With Color Vision
The Y Chromosome Is Missing Them All
Therefore, Males Are Particularly Vulnerable To Colorblindness

11. Colorblindness The Images Below are NOT Diagnostic

12. Red-Green Colorblindness
Most Common Form
1:10 Males
1:100 In Females
Why The Difference?

13. (only daughters will receive the fathers X Chromosome)
Colorblindness
Colorblind Males Only Pass The Recessive Allele On To Their Daughters It is not on the Y Chromosome They Pass To Their Sons.
(only daughters will receive the fathers X Chromosome)
Thus - The Gene Appears To Skip A Generation And Will Only Reappear In His Grandchildren

14. Hemophilia Two Important Blood Clotting Genes Are On The X Chromosome
Occurrence Rate = 1:10,000 Males

15. Mild Post-Injection Bleeding In A Patient With Hemophilia

16. Duchenne Muscular Dystrophy
Sex-Linked Abnormal Muscle Protein Patients Rarely Live Beyond Early Adulthood Occurrence Rate = 1:3000 Males

17. In Mammals Female X-Chromosome InactivationNO
Males
Only Have (1) X Chromosome
Females Have Two (2) X Chromosomes
Do Female Express
Both X Chromosomes?

18. In Mammals Female X-Chromosome Inactivation
One X Chromosome Is Randomly Switched Off
That Chromosome Forms A Dense Region In The Nucleus Known As A Barr Body

19. In Mammals Female X-Chromosome Inactivation
Arrows Indicate Barr Bodies

20. In Mammals Female X-Chromosome Inactivation

21. During Meiosis, Homologous Chromosomes Fail To Separate
Chromosome Disorders
Most Common Is Nondisjunction
During Meiosis, Homologous Chromosomes Fail To Separate
One Gamete Will Have An Extra Chromosome (Trisomy) The Other Will Have One Less

22. Down Syndrome Nondisjunction of Chromosome 21 (trisomy)
Occurs 1:800 Births
Mental Retardation May Be Mild To Severe
Increased Susceptibility To Disease

23. Down Syndrome Why Would 3 Copies Cause Problems When 2 Copies Don’t?
Don’t Know Yet
Working Hard To Find Out

24. Sex Chromosome Disorders
Turner’s Syndrome
Females
Nondisjunction Results In A
XO Female
Sterile
Sex Organs Do Not Develop During Puberty

25. Sex Chromosome Disorders
Klinefelter’s Syndrome
Males
Nondisjunction Results In A XXY Male
The Extra X Interferes With Meiosis – Generally Sterile
Also Found XXXY & XXXXY
Exhibit Female Body Patterns In Hips, Partial Breast Development, Female Pubic Hair Pattern

26. Sex Chromosome Disorders
No Babies Are Born Without At Least One X Chromosome Indicates The X Chromosome Carries At Least One Gene Required For Life

27. No “Y” Present – Embryo Develops As A Female
Y Chromosome
If Present, Individual Is Male
Even When Multiple X Chromosomes Are Present
Contains At Least One Gene Required For Male Sexual Development
No “Y” Present – Embryo Develops As A Female