University of North Carolina

BIO 101

Patterns of Inheritance I

1)Why is that the Inuit people of the artic can eat an extremely high fat diet, yet suffer less from heart attacks than people living in the United States?

2. Which themes of biology are demonstrated in this chapter introduction?

3. What made the pea plant a good model for studying genetics (as opposed to say humans)?

4. One important aspect for Mendel was that he had pea plants that could “breed true”, what does this mean? For example, if a plant was a purebreeding purple flower plant, what does this indicate about the plant’s two alleles that code for flower color?

5. Take time to be sure you know the “terms used in modern genetics” in section 9.3 that are bold-faced. You need a good understanding of these terms to speak like a geneticist. List here any that you are not already familiar with and define them. These terms should become more obvious as you start applying them in the next section too.

6. What type of offspring will they make if the gametes of these two parents fuse through fertilization?

7. Practice constructing a Punnett square when a purple heterozygote (Pp) is crossed to another purple heterozygote (Pp). What will be the phenotypes of the offspring and in what ratio will they be to each other?

8. What is similar about homologous chromosomes? What might be different?

9. When an organism that is heterozygous for two genes (RrYy) is crossed to another organism that is the same genotype (RrYy) the phenotypic ratio will always be what? (Dihybrid x dihybrid):

10. What fraction will have the dominant phenotype for both traits?

11. What fraction will have the dominant phenotype for trait A (and be recessive for B)? _________What fraction will have the dominant phenotype for trait B (and be recessive for a)?What fraction will have the recessive phenotype for both traits?

12. Using the traits in Labradors discussed in the book, predict the phenotype of offspring obtained by mating a black Lab (homozygous for coat color and normal vision) with a chocolate Lab that is blind from PRA.

13. What is a testcross useful for?

14. What is the genotype of one of the individuals that is always crossed in a testcross?

(We call this individual a tester)

15. Using the rule of multiplication, what is the chance that a woman who is pregnant four different times will give rise to a family with four sons?

16. What is the difference between these shapes when they are filled in vs. not filled in?

17. What is the probability that two individuals who are carriers for the cystic fibrosis will have a child with cystic fibrosis?

18. Describe the symptoms of cystic fibrosis.

19. Many people incorrectly think that a dominant trait is more common in a population. Using achondroplasia as an example, explain how this cannot be true.

20. If a woman has a parent with Huntington’s disease (and the other parent is normal) what is the chance that she too will have inherited the lethal Huntington allele?

21. Why might an adult want to be genetically tested?

22. Why might a fetus be genetically tested?

23. Traditionally, amniocentesis was used to confirm chromosomal abnormalities like Down syndrome.

What is the risk associated with this test? Are there less invasive tests that look at Down Syndome risk factors?

24. How many autosomes are in the human male?Sex chromosomes?

How is it possible that a baby is born with the XY chromosomes but does not develop as a male but instead has ovaries?

25. As described in 9.21, “white eyes” is an x-linked recessive trait in fruit flies. A female fruit fly that is heterozygous is crossed with a red-eyed male. What are the possible offspring? (Set up a Punnett square.) What if the male was white eyed instead? (Use Figure 9.21 to check your understanding after you try this!)

26. What clue might you have that a human disorder is X-linked?