GENETICS WORKSHEET
NAME________________________
USE YOUR NOTES, TEXTBOOK OR OTHER RESOURCES TO ANSWER THE FOLLOWING QUESTIONS ABOUT
GENETICS AND PUNNETT SQUARES.
1. What is the difference between genotype and phenotype? Genotype is the actual genes
present in an organism; phenotype is the expression of the genes (appearance)
2. What is a gamete? A haploid reproductive cell (egg, sperm)
3. What is an allele? An alternate form of a gene (e.g., round and wrinkled are both alleles for
the trait “seed shape”)
4. What is the difference between a homozygous and heterozygous gene pair? Homozygous pairs
= both alleles are the same form of the trait; heterozygous = both alleles are different
5. How many forms of a trait can a parent give its offspring? Only 1
6. What is the probability of an offspring of any species being male or female? 50%
7. Which gamete determines the sex of an organism? The sperm, because it may contain the Y
chromosome. Eggs contain only X chromosomes
8. What is a sex-linked trait? a trait that is on the sex chromosome, generally the X chromosome.
Some examples are hemophilia, baldness, and colorblindness
9. What is the difference between dominance as Mendel knew it and incomplete dominance?
With complete dominance, one allele completely masks the presence of the other in the
phenotype; with incomplete dominance, neither allele is fully expressed, resulting in a third
phenotype somewhere between the two heterozygotes. For example, certain flowers may be
either red or white in each homozygote, but pink in the heterozygote.
10. Why can parents have seven boys and one girl, even though that is not the correct probability?
Because of the random uniting of the egg and sperm, and the fact that each event is
independent of the other. Once born, a child has no influence over which egg and sperm will
encounter each other if his parents have another child.
11. Which of the following would be the best sample to use to determine the probability of a trait
a. 1 family
b.
100 families
c.
900 families
d. 10 families
e.
6 families
PUNNETT SQUARES: PERFORM A PUNNETT SQUARE TO DETERMINE THE PROBABILITY OF THE
OCCURANCE OF A TRAIT IN THE FOLLOWING PROBLEMS (GENOTYPIC AND PHENOTYPIC)
a. What is the probability of offspring having the following trait if these parents are crossed?
Homozygous tall pea plant
x
heterozygous tall pea plant
Genotypic: 50% TT, 50% Tt
Phenotypic: 100% tall
b. What is the probability of offspring having the following trait if these parents are crossed?
Heterozygous black mouse
x
homozygous brown mouse
Genotypic: 50% Bb, 50% bb
Phenotypic: 50% black, 50% brown
c. What is the probability of offspring having the following two traits if these parents are
crossed in pea plants?
Heterozygous tall
Heterozygous yellow
x
x
homozygous short
homozygous green
Genotypic: 1 TtYy : 1 Ttyy : 1 ttYy : 1 ttyy
Phenotypic: ¼ tall, yellow : ¼ tall, green : ¼ short, yellow : ¼ short, green