Chapter 5 Test Review
Name ________________________________
Period __
Date __-__-__
Chapter 5, Section 1 (Day 1)
In the mid-nineteenth century, a priest named Gregor Mendel tended a garden in a central
European monastery.
Heredity is the passing of physical characteristics from parents to offspring.
Mendel experimented with thousands of pea plants to understand the process of heredity.
Chapter 5, Section 1 (Day 2)
Mendel reached several conclusions on the basis of his experimental results.
The factors that control each trait exist in pairs.
The male and female parents contribute one factor each.
One factor in a pair can hide the other factor.
Today, scientists use the word gene for the factors that control a trait.
Alleles are the different forms of a gene.
A dominant allele is one whose trait always shows up in the organism when the allele is
present.
A recessive allele is hidden whenever the dominant allele is present.
A dominant allele is represented by a capital letter.
A recessive allele is represented by the lowercase of the same letter.
Two dominant alleles for tall, its written as TT.
Two recessive alleles for short, its written as tt.
One allele for tall stems and one allele for short stems, its written as Tt.
5.2 Probability
Probability is a number that describes how likely it is that a certain event will occur.
A Punnett square is a chart that shows all the possible combinations of alleles that can result
from a genetic cross.
1. T T
2. t t
3. T T
4. T t
5. T T
6. T t
T TT TT
t tt tt
t Tt Tt
T TT Tt
T TT TT
t Tt tt
T TT TT
t tt tt
t Tt Tt
t Tt tt
t Tt Tt
t Tt tt
What is the probability that the pea plant will be tall and short in each Punnett square?
1.T____t____ 2. T____t____
3. T____t____
4. T____t____
5. T____t____
6. T____t____
An organism’s phenotype is its physical appearance, or visible traits.
An organism’s genotype is its genetic makeup, or allele combinations.
An organism that has two identical alleles for a trait is said to be homozygous for that trait.
An organism that has two different alleles for a trait is heterozygous.
In codominance, the alleles are neither dominant nor recessive. As a result, both alleles are
expressed in the offspring.
5.3 The Cell and Inheritance
The body cells of a human have 46 chromosomes.
Human’s sex cells (egg and sperm) have only 23 chromosomes.
The fertilized human egg had 46 chromosomes, or 23 pairs.
Genes are carried from parents to their offspring on chromosomes.
Meiosis is the process by which the number of chromosomes is reduced by half to form sex cells,
sperm and eggs.
Each of your chromosomes contains about 35,000 genes. Each gene controls a trait.
5.4 Genes, DNA, and Proteins
The main function of genes (DNA) is to control the production of proteins in an organism’s cells.
A DNA molecule is made up of four different nitrogen bases—adenine (A), thymine (T),
guanine (G), and cytosine (C). These bases form the rungs of the DNA “ladder.”
P
S
P
A
T
P
S
G
S
C
P
C
S
G
P
S
Phosphate
Group
P
P
S
S
Sugar Group
P
T
A
S
A single gene may contain a million or more of these bases.
The order of the bases forms a genetic code that specifies the type of protein produced.
A group of three DNA bases codes for one amino acid.
Amino acids are the building blocks of proteins.
A mutation is any change in a gene or chromosome.