A Gloomy Clock

Introduction Genetics is the science that explains the variation and transmission of inherited characteristics from parents to offspring. The basic laws of heredity became popular to science in 1865, with the publication of the works of Gregor Mendel, the father of genetics. He observed that by breeding pairs of different varieties of peas, the offspring resembled one of the parents. This inspired him to continue his work that resulted to more experiments on plants. Before starting this exercise, read the discussion that comes before this activity. Knowledge of how genes separate and recombine when chromosomes undergo meiosis is basic to the understanding of heredity.

Objective After this exercise, the students should be able to:
1. Understand the mechanisms of heredity and explain the variation that exists among parents and offspring.

Procedure
1. Determine which of the following traits are dominant and which are recessive by making a statistical survey of the following traits in the class.
Traits
Number of Students Proportion
Attached earlobes
19
19/49
Unattached earlobes
30
30/49
Right-handed
31
31/49
Left-handed
18
18/49
Ability to roll tongue
25
25/49
Inability to roll tongue
24
24/49
Curly hair
3
3/49
Straight hair
33
33/49
With 10 fingers
48
48/49
With 11-12 fingers
1
1/49
2. Solve the following problem. In fruit flies, gray is dominant over black. If pure bred gray fruit fly crosses with a black fruit fly, what percent of the offspring will be gray?
GG = homozygous gray fruit fly gg = homozygous black fruit fly

G
G
g
Gg
Gg g Gg
Gg

Genotype: Gg; Gg; Gg; Gg Phenotype: Gray; Gray; Gray; Gray 100% Gg 100% Gray

3. The law of probability states that the chance (or probability) of the simultaneous occurrence of two or more independent events is equal to the product of the probabilities that each will occur separately. Thus, when a coin is