Empty Outline 9

Genetics

Use Chapter 14 as a Reference

Directions:

• Complete using your textbook to find answers to the following questions. Next week we will spend going over this information and answering any questions that come up. Good luck and have fun!

Outline Grading Criteria

• Outline shows a conscientious effort to be complete and explain the questions posed. Most answers are correct.
• Student shows depth of answers by explaining, defining, and giving examples where appropriate. If there is a sentence or less for each question, this grading criteria is not met.

1. Define the following terms:

Gene

Allele

Gonad

Meiosis

Gamete

Diploid

Haploid

Zygote

Sex Chromosome

Autosome

Homologous

Homozygous

Heterozygous

Dominant

Recessive

Phenotype

Genotype

Character

Trait

X-linked traits

2. Distinguish between an individual’s “genotype” and their “phenotype”. Give an example.

3. Use the terms “dominant” and “recessive” in defining the following:

Heterozygous:

Homozygous:

4. What is a “gene” as defined by a Mendelian geneticist?

5. What is the relationship between a gene and an allele? Support your response with an example.

6. State Mendel’s two laws in your own words. Include a simple diagram to illustrate each.

Mendel’s 1st Law:

Mendel’s 2nd Law:

To review and/or get a good introduction, see the student CD, chapter 14, activities. They cover the monohybrid crosses, dihybrid crosses, and other concepts you need to know for this outline and this week.

7. In Drosophila, black body color is recessive to gray body color. a geneticist had three pairs of flies with gray body color designated A, B, and C. The crosses she made and their results are tabulated below.

	F1 Generation
Parental Cross	Gray body	Black body	Ratio
A x B	109	0	100% Gray- bodied
A x C	80	28	2.86 : 1
B x C	76	0	100% Gray- bodied

a. What are the genotypes of A, B, and C? Justify your responses. Use Punnett squares where appropriate.

b. What are the expected phenotypic and genotypic ratios when flies A, B, and C are crossed with flies having black bodies?. Use Punnett squares where appropriate to justify your response.

8. Below are the results of a few of Mendel’s F₁ monohybrid crosses involving various characteristics in pea plants. Use these results to answer the questions that follow.

Character	Dominant Trait	x	Recessive Trait	F2 Generation Dominant : Recessive	Ratio
Height	Tall	x	Dwarf	787 : 277
Pod color	Green	x	Yellow	428 : 152
Flower color	Purple	x	White	705 : 224

a. Calculate the ratio of the F₂ generation offspring for each cross. Record your responses in the table above.

b. Discuss how the results of these crosses led Mendel to his first law, the law of segregation.

9. Below are the results from Mendel’s dihybrid cross between true-breeding (i.e. homozygous) parent plants differing in two traits, flower color and height.

Generation	Phenotypes
Parents	(Purple-flowered, tall) x (white-flowered, dwarf)
F1	100% purple-flowered, tall
F2	630 purple-flowered, tall
	216 purple-flowered, dwarf
	202 white-flowered, tall
	64 white-flowered, dwarf

a. Calculate the phenotypic ratio for the F₂.

Compare the expected phenotypic ratio for the F₂ with that obtained by Mendel in the table above. Explain why they are different.

b. Discuss how the results of these crosses led Mendel to his second law, the law of independent assortment.

c. What would be the expected phenotypic ratios for the F₁ and the F₂ if pairs of alleles segregated together (i.e. dependent assortment), rather than assorting independently. Justify your response.

10. Which of Mendel’s Laws are best illustrated by the events that occur in the process of meiosis?

11. Do laws prohibiting marriages between brothers and sisters make biological sense? Explain in terms of recessive traits.

12. How could you determine if an individual really is pure-breeding for all traits?

13. Complete dominance and incomplete dominance differ in the amount of variation seen in the offspring.

a. How many genotypes are possible with complete dominance involving two alleles? List them.

How many phenotypes are possible? List them.

b. How many genotypes are possible with incomplete dominance involving two alleles? List them.

How many phenotypes are possible? List them.

14. Why is a recessive sex-linked allele always expressed in human males, but not always expressed in females?

15. Make a diagram of an unduplicated chromosome containing two different genes, gene A and gene B. Use this diagram to explain gene locus and gene linkage.

b. Why does gene linkage interfere with independent assortment?

c. Suppose the genotype of an organism is AaBb. If the genes A and B are linked on one chromosome (as in part a, above), and their recessive alleles, a and b, are on the other homologue, how many different genetic types of gametes would be produced in the absence of crossover? List them. Note: You should be able makes a diagram of meiosis to show how these gametes would be produced.