14-2 Human Chromosomes – Reading Guide NAME:_____________________________________

1. Genes make up only a small part of chromosomes; only about _________% of chromosome’s DNA functions as genes.

2. The first two human chromosomes whose sequences were determined were chromosome ______ & ______.

3. Chromosome 21 contains about _______ genes, including one associated with amyotropic lateral sclerosis (ALS).

4. ALS is also known as _____________ ___________________ _______________________.

5. Describe the effect of ALS. ______________________________________________________________________

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6. Genes on the X and Y chromosome are said to be ___________________ - _______________ _____________

7. Which sex chromosome carries more genes? X or Y ( circle one)

8. Colorblindness is the inability to distinguish certain color. What is the most common form of this disorder? __________________________________________________________

9. Males have just one __________ chromosome. So, all X-linked alleles are expressed in ____________ even if they are ______________________.

10. ________________________ is another example of a sex-linked disorder in which two genes on the X chromosome help control ___________________ ____________________________.

11. Duchenne Muscular Dystrophy is a sex-linked disorder that results in ___________________ ________________ and ________________________________________________________.

12. In the U.S. one out of every _____________ males is born with Duchenne M.D.

13. Females have two X chromosomes, males have only one. How does the cell “adjust” to the extra X chromosome in female cells?______________________________________________________________________________

14. The turned-off chromosome forms a dense region in the nucleus known as a ________________ __________.

15. Drawing conclusions: After reading the section on X-Chromosome inactivation, look at fig 14-14. Is the cat shown a male or a female? ___________________________

16. The error in meiosis when nonhomologous ________________________ fail to separate is called _______________________________.

17. Nondisjunction causes ___________________ to have abnormal numbers of chromosomes.

18. Three copies of an autosomal chromosome is known as ___________________________.

19. The most common form of trisomy is trisomy 21 and is called _______________ _______________________.

20. Give two examples of nondisjunction among the sex chromosomes. ____________________________________

21. What is the sex of an individual with Turner’s syndrome? ___________________

22. How many chromosomes does an individual with Klinefelter’s syndrome generally have? _________________