Name: __________________________
SCIENCE – GENETICS
G-2a
May 27, 2008
Section #/color: ____ / ________
SCIENCE – GENETICS
What and who are the basic principles of genetics? What is a Punnett Square and how do we use it
to the traits of an offspring?
A REVIEW CHECK-UP for PACKET I.
DIRECTIONS: To see how you’re did with part one of your GENETICS two-part mini-series,
give the following tasks a try.
PART I. FOUNDATION OF GENETICS
Read each of the following statements about the foundations of genetics. Determine whether or not
the underline part of each statement is true or false. If it is true, write “TRUE” in the blank next to the
statement. If it is false, write “FALSE” in the blank next to the statement and CHANGE the underlined
part of the statement to make it true.
___________ 1. Chromosomes are found in the nucleus. They are made of ATP, a substance
composed mostly of glucose and they carry the jeans that help to determine an organism’s traits.
___________ 2. An allele refers to one member of a gene pair on a chromosome pair. There are 23
gene pairs in the somatic cells of every human and 23 single genes in the sex cells of every human.
___________ 3. An offspring inherits its chromosomes from its parents. Half its chromosomes come
from the father and half of its chromosomes come from the mother.
___________ 4. The genotype of an offspring describes what alleles it has for that trait (e.g. TT, Tt
or tt) and the phenotype of and offspring describes what an organism’s traits actually look like (e.g.
tall or short).
___________ 5. Organisms that are recessive for a trait must have two alleles that are also
recessive. Organisms that are purebred dominant for a trait must have two alleles that are both
dominant. Organisms that are hybrid for a trait must have one dominant and one recessive allele.
___________ 6. If green seeds in pea plants are dominant to yellow seeds, the correct genotype for
a hybrid would be Yy and for a purebred recessive would be gg.
___________ 7. An example of incomplete dominance is when you have a grey-haired cat produced
from a white-haired mother cat and a black-haired father cat. An example of codominance is when
you have a white-haired mother cat and a black-haired father cat produce a black and white-haired
offspring.
___________ 8. Mutations only result in negative outcomes and are only caused by environmental
factors called mutagens. They can occur when a gene on a chromosome becomes lost, turned
around, or detached and reattached to another chromosome.
___________ 9. Genes for different traits are inherited together. For example, the gene for red hair
and for having freckles are always inherited together.
___________ 10. Genetics is based on the mathematical concept of probability. Because each
parent donates one allele for a trait, there are always four possible offspring outcomes. Punnett
squares help us to predict the phenotype and genotypes of these four possible offspring outcomes.
PART II. PUNNETT SQUARES
Create and interpret a Punnett Square for the following situation. Write the correct allele letters for
the parents and offspring in the blanks and boxes provided. List the outcome probability (percent and
fraction) of phenotype and genotype in the table provided.
In Mendel’s experiment with pea plants, he studied several different traits of pea plants. He discovered that
the dominant trait for seed shape was round and the recessive trait was wrinkled. Assume that a hybrid
plant for seed shape and a purebred recessive plant for seed shape are “crossed” (i.e. mated) with one
another.
____
____
OUTCOME PERCENT FRACTION
Round
____
phenotype
Wrinkled
phenotype
____
Purebred
dominant
Hybrid
Purebred
recessive