Name:________________________ Class Period:___________________
Mendel and Heredity
Many of your characteristics including the color and
shape of your eyes and the texture of your hair resemble those
of you parents. The passing of characters from parents to
offspring is called heredity. From the beginning of recorded
history, humans have attempted to alter crop plants and
domestic animals to give them traits that are more useful to us.
Before DNA and chromosomes were discovered, heredity was
one of the greatest mysteries of science.
Mendel carried out experiments in which he bred different
varieties of garden pea Pisum sativum. British farmers had
performed similar breeding experiments more than 200 years
earlier. But Mendel was the first to develop rules that accurately
predict patterns of heredity. The patterns that Mendel
discovered form the basis of genetics, the branch of biology
that focuses on heredity.
1. Compare and contrast between heredity and genetics.
Mendel’s initial experiments were monohybrid crosses. A
monohybrid cross is a cross that involves one pair of contrasting
traits. For example, crossing a plant with purple flowers and a
plant with white flowers is a monohybrid cross. Mendel carried
out his experiments in three steps.
2. What does the term “cross” refer to?
Step 1 – Mendel allowed each variety of garden pea to selfpollinate for several generations. This ensured that each variety
was true- breeding for a particular character; that is, all the
offspring would display only one form of the character. For
example, a true-breeding purple-flowering plant should
produce only plants with purple flowers in subsequent
generations.
These true-breeding plants served as the parental generation in
Mendel’s experiments. The parental generation, or P
generation, are the first two individuals that are crossed in a
breeding experiment.
Step 2- Mendel then cross-pollinated two P generation plants
that had contrasting traits, such as purple flowers and white
flowers. Mendel called the offspring of the P generation the fist
filial generation, or F1 generation. He then examined each F1
plant and recorded the number of F1 plants expressing each
trait.
Step 3- Finally, Mendel allowed the F1 generation to selfpollinate. He called the offspring of the F1 generation plants
the second filial generation, or F2 generation. Again, each F2
plant was characterized and counted.
3. Explain each term.
A. True-breeding
B. P generation
C. F1 generation
D. F2 generation
Mendel’s Hypotheses
 For each inherited character, an individual has two
copies of the gene- one from each parent.
 There are alternative versions of genes. From example,
the gene for flower color in peas can exist in a “purple’
version or a “white” version. Today the different versions
of a gene are called its alleles. An individual receives
one allele from each parent. Each allele can be asked
on when the individual reproduces.
 When two different alleles occur together, one of them
may be completely expressed, while the other by have
no observable effect on the organism’s appearance.
Mendel described the expressed form of the character
as dominant. The trait that was not expressed when the
dominant form of the character was present was
described as recessive.
 When gametes are formed, the alleles for each gene in
an individual separate independently of one another.
Thus, gametes carry only one allele for each inherited
character. When gametes untie during fertilization,
each gamete contributes one allele. Each parent can
contribute only one of the alleles because of the way
gametes are produced during the process of meiosis.
4. In your own words, explain the four major hypotheses
Mendel developed
5. In your own words, explain the following terms:
AlleleDominantRecessive-