Study Guide for Test 4

chapter 12

1. Mendel studied the inherited traits of peas. Before Mendel, what did people think about the blending of traits? What did he discover about inheritance? Are traits ever blended?

2. What is independant assortment? describe it with chromosomes. Describe what Mendel knew about it. Be able to explain when it DOES NOT WORK (i.e. when traits have "genetic linkage")

3. What is a genotype? What is a phenotype? How are they different? What does it mean if we say a gene is "expressed"

4. What are somatic cells? What are gametes? Which are diploid? Which are haploid?

5. Explain what sex chromosomes and autosomes are. How many sex chromosomes are contained in MOST mammal gametes?

6. What is an allele? What does it mean to be heterozygous? What does it mean to be homozygous?

7. Explain what genetic diversity is

8. What is a hybrid? What is a dihybrid?

9. Be able to explain the difference in dominance (sometimes called complete dominance), incomplete dominance, and codominance. Can all three of these systems still have a recessive? What would the heterozygote phenotype be fore each of these three system.

10. What type of dominance do we see in blood typing? Which genotypes can cause the Type A phenotype? Which genotypes can cause the Type B pheonotype? Which genotypes can cause the Type O phenotype?

11. Know the magic ratios - 3:1, 1:2:1, 9:3:3:1. For each ratio, be able to explain what the ratio could tell us about the genotype and phenotype of the P1, F1 and F2 generation.

12. In a dihybrid cross, what is the ratio that applies to each trait if it is examined by itsself?

13. Why is it wrong to talk about a "Law" of segregation? Why was Mendel lucky (i.e. what two things about the traits he studied made his work easier than it could have been?)

14. Know some examples of gene expression that is controlled by temperature

15. know an example of gene expression that is controlled by nutrients or pH

16. What does it mean if a trait is multigenic or polygenic? What does it mean if the trait is pleitrophic?

17. In a multigenic trait, which genes can affect the phenotype. (be able to explain the mouse example.)

chapter 13

1. What is a chromosome? What is a gene? What is a locus? Be able to explain the relationship between these terms

2. How many chromosomes do humans have? How many of them are autosomes? How many are sex chromosomes? Which sex chromosomes cause a human to be female? Which sex chromosomes cause a human to be male?

3. How many genes do we estimate that humans have?

4. What is a sex linked trait? Which sex is most likely to be affected by a negative recessive trait on an X chromosome? Which sex is most likely to be affected by a negative Y linked recessive trait? Which sex would be most likely to be affected by a DOMINANT recessive trait?

5. Which sex is more likely to have pattern baldness? Which sex is more likely to have color blindness? Why?

6. What does the SRY gene do? Which chromosome is it found on?

7. There are four sources of genetic variation. One of them is mutation. What are the other three?

8. What does it mean if we say that chromosomes are “genetically linked”? Explain how crossing over can end this linkage. This means that Mendel’s “law” about segregation is more of a suggestion. Explain why

9. Imagine two traits that are very dangerous or even lethal. These traits are not related to each other, and are not on the same chromosome. One of these traits is dominant, the other is recessive. Which one (dominant or recessive) is more likely to be lethal to people who have the bad allele? Which one is more likely to be removed through natural selection? Which one is likely to be more common in the population?

10. What is a “carrier” for a trait? Are they homozygous dominant, homozygous recessive or heterozygous?

11. It is possible to have a dihybrid cross that is NOT 9:3:3:1. Explain one what that this could happen. (HINT: independent assortment.)

12. What is the difference in somatic mutations and gametic mutations? Which one is more likely to be passed on to an offspring.

13. Be able to define these terms: aneuploidy, monosomy, trisomy, non-disjunction

14. What causes Down syndrome? Which chromosome is involved?

15. Explain the link between maternal age, non-disjunction and spindle fibers

16. When is having an abnormal number of chromosomes more likely to be lethal?

17. Be able to explain, and recognize pictures of: insertion, deletion, inversion, translocation and duplication