Download Genetics Problem Set #1

IB Ecology Genetics Problem Set #1 Monohybrid and Dihybrid Crosses + Multiplication Rule
Follows Campbell’s Chapter 14 pg. 267- 289. Directions: 1. Do the following on separate paper.2. Write out punnett
squares for all problems but #2 and #5. 3. Show all calculations.
1. Monohybrid cross problem:
A tall pea plant is crossed with a recessive dwarf pea plant. What will the phenotypic and
genotypic ratio of offspring be- a. -if the tall plant was TT? b. -if the tall plant was Tt?
2. Look at Figure 14.8 on page 274. This is a classic example of independent of assortment of the
genes for two traits giving you a classic 9:3:3:1 ratio also known as a dihybrid cross. Mendel’s law of
independent assortment is about how the appearance of one trait in an organism is not related to the
appearance of another. Because of the 4 major disruptive factors during meiosis, one gene will not
influence where another gene goes. Independent assortment means that the genes are either on
different chromosomes or they are so far away on the same chromosome that crossing over creates a
situation where they behave independently. When solving dihybrid problems you usually assume
that independent assortment is taking place.
Let’s assume that I conducted an experiment and collected 1000 seeds.
Approximately how many of each phenotype should there be?
3. A true-breeding tall, purple-flowered pea plant (TTPP) is crossed with a true-breeding dwarf,
white-flowered plant (ttpp).
a. What is the phenotype of the F1 generation?
Compare the F2 generation to the parental F1
b. What is the genotype of the F1 generation?
c. What four types of gametes are formed by
F1 plants during meiosis?
d. Conduct a dihybrid cross to show the
offspring in the F2 generation.
e. Recombinants are offspring that are
different from the parental phenotypes.
generation and circle the recombinants in the
F2 generation.
f. Conduct another dihybrid cross if the female
plant has the genotype TtPP and the male
plant has the genotype ttPp. Try it using a 2x2
table!
4. Cross a Tt CRCW (Tall, Pink flowers) x Tt CRCW and show break down the predicted phenotypic
ratios for the F1 generation. Hint: Flower color is showing incomplete dominance (IB also calls this
codominant)—see page 277 of your book.
Tall red =
Dwarf red =
Tall pink=
Dwarf pink=
Tall white=
Dwarf white =
5. For the following crosses, determine the probability of obtaining the indicated genotype in an
offspring. The first one is done for you. You need to do a punnett square in your head for each letter
and then use the multiplication rule.
Cross
Offspring
Answer and Probability
AAbb x AaBb
AAbb
½ to get AA x ½ to get bb = 1/4
AaBB x AaBb
aaBB
AABbcc x aabbCC
AaBbCc
AaBbCc x AaBbcc
aabbcc
6. Fruit fly notation is archaic! The normal phenotype for a character is called the wild type and is
shown with a “+” sign as a superscript. The alternative form is called the mutant and is shown with a
letter. See page 294-5 and Figure 15.9 on page 299 (explained on pg. 301. Cross a b+bvg+vg x
b+bvgvg. Write out the probabilities of the phenotypes.