1. 14-2
Human Chromosomes

2. Human Genes and Chromosomes
If human DNA sequence were written as a textbook it would be more than 4 million pages
The human genome is spread out onto 23 pairs of chromosomes
22 pairs are autosomes
One pair is sex chromosomes

3. Sex-Linked Genes
sex-linked genes: genes located on the sex chromosomes
more than 100 disorders mapped on “X” chromosome
“Y” chromosome smaller and contains fewer genes
colorblindness
Inability to see certain colors
rare in females because they need two recessive alleles to express trait
males produce daughters that are carriers of disorder

4. What numbers (if any) do you see…?

5. What numbers (if any) do you see…?
An individual with normal color vision will see a 5 revealed in the dot pattern.
An individual with Red/Green color blindness will see a 2 revealed in the dots.

6. Father
(normal vision)
Normal vision
Colorblind
Male
Female
Daughter
(normal vision)
Son
(normal vision)
Mother (carrier)
Daughter
(carrier)
Son
(colorblind)

7. Father
(normal vision)
Normal vision
Colorblind
Male
Female
Daughter
(normal vision)
Son
(normal vision)
Mother (carrier)
Daughter
(carrier)
Son
(colorblind)

8. X-Chromosome Inactivation
hemophilia
caused by recessive allele in one of two genes on “X” that control clotting
can bleed to death from cuts, bumps, or bruises
duchenne muscular dystrophy
sex-linked disorder that results in the progressive weakening and loss of skeletal muscle
caused by defective gene that codes for a muscle protein
X-Chromosome Inactivation
In female cells, one “X” chromosome is randomly switched off
Forms a dense region in nucleus called a Barr body

9. Chromosomal Disorders
nondisjunction: the failure of homologous chromosomes to separate during meiosis I
Results in zygotes with abnormal chromosomes numbers
Causes aneuploidy
Monosomy- missing one chromosome
Trisomy- extra chromosome
Downs syndrome (47)
also know as trisomy 21
causes mental retardation, oversized tongue, eye deformation
Sex chromosome disorders
Turner’s syndrome (XO) 45 chromosomes
Kleinfelter’s syndrome (XXY) 47 chromosomes
Metafemales (XXX) 47 or more
Jacob’s (XYY) 47

10. Homologous chromosomes fail to separate
Meiosis I:
Nondisjunction
Meiosis II

11. Homologous chromosomes fail to separate
Meiosis I:
Nondisjunction
Meiosis II

12. Homologous chromosomes fail to separate
Meiosis I:
Nondisjunction
Meiosis II