EXERCISE 12
GENETIC INHERITANCE PROBLEMS
OBJECTIVES
Note:
A lleles
locus
P 1 generation
F
1 g eneration
Note:
Genetics Inheritance Problems
Instructions: Work in lab groups to count kernels and solve the genetics problems. Materials: Genetic corn cobs with kernels, calculator
1. CROSS # 1:
corn kernels (seeds)
purple
yellow
F1 p lants that all had purple corn kernels
Po generation:
Genotype F1
The F1 corn plants with the purple corn kernels were interbred
2
F1 cross:
F2 generation:
e xpected F2
expected percentage
P rocedure: The F2
c ontainer in the lab labeled F2 of
C ross 1 observed
TABLE 1: Phenotypes of Corn Kernels for F2 Generation of Cross 1 (observed data)
6
4
2
2
TABLE 2: Observed and expected data for F2 generation of Cross 1
2
2.
CROSS # 2:
F1 purple corn kernels with yellow corn kernels.
F
F1
F2 generation:
e xpected F2
expected percentage
Procedure:
of cross 2.
observed
TABLE 3: Phenotypes of Corn Kernels for F2 Generation of Cross 2 (observed data)6
4
2
observed expected.
TABLE 4: Observed and expected data for F2 generation of Cross 2
3.
CROSS # 3:
purple, wrinkled seeds
(kernels) yellow, smooth seeds (kernels)
purple and smooth.
Write in the parents genotypes (Po generation) and the genotype of their
Po generation:
F1 generation:
2
F1 cross:
F2 generation:
e xpected F2
P rocedure: The F2
c ontainer in the lab labeled F2 of
C ross 3. t en observed
TABLE 5: Phenotypes of Corn Kernels for F2 Generation of Cross 3 (observed data)
2
4
6
9
TABLE 6: Number observed and expected data for F2 generation of Cross 3
TABLE 7: Percent observed and expected data for F2 generation of Cross 3
P ×
P ×
F
Lab Exercise 12
If two wavy-haired parents had twelve children, how many of their offspring would be expected to be curly? Wavy? Straight?
5. A woman with normal vision, whose father was color-blind, married a man who had normal vision. The genes for normal vision and color-blind vision are on the X chromosome. The color
blind characteristic is recessive. What are the expected F1 genotypes and F1 phenotypic ratio from this mating?
P1 cross:
Gametes: Punnett Square:
F1 genotypes:
F1 phenotypic ratio:
Questions:
1. State Mendel’s First . What part of meiosis is the basis for this law?
2. State Mendel’s Second . What part of the meiotic process is the basis for this law?
287
Lab Exercise 12
3. Why do we use Punnett squares to solve genetics problems?
4. All of the genetics problems in this lab exercise involved monogenic traits. In reality however, most genetic traits are polygenic. Compare monogenic traits with polygenic traits. Which traits are easier to predict outcomes from matings?
5. (OPTIONAL) If genetic engineering (gene technology) is ever successful in curing people of a genetic disease, would the disease more likely be monogenic or polygenic? Why?
288
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