Introduction To Genetics-
I. The work of Gregor Mendel
A. Gregor Mendel was born in 1822
and after becoming a priest; Mendel
was a math teacher for 14 years and a
monastery. Mendel was also in charge
of the monastery garden.
1. Mendel carried out
his work with
2. Fertilization is the fusion of an egg
and a sperm.
3. True breeding plants are plants that
were allowed to self-pollinate and the
offspring would be exactly like the
B. Genes and Dominance
1. The different forms of a gene is
called and an alleles.
2. The principal of dominance states
that some alleles are dominant and
others are recessive.
Pinky Finger Traits
At John Burke High School they tested dominant and recessive traits in
our school population. We tested pinky finger traits, whereby, the bent
finger is dominant and the straight finger is recessive.
1. Each trait has two genes, one from the
mother and one from the father.
2. Traits can be either dominant or recessive.
3. A dominant trait only needs one gene in
order to be expressed.
4. A recessive trait needs two genes in
order to be expressed.
5. Egg and sperm are sex cells called
6. Segregation is the separation of
alleles during gamete formation.
II. Probability and Punnett
A. Genetics and Probability
1. The likelihood that a particular
event will occur is called probability.
2. The principals of probability can be
used to predict the outcome of genetic
B. Punnett Squares
1. The gene combination that might result
from a genetic cross can be determined by
drawing a diagram known as a Punnett
2. Punnett squares can be used to predict
and compare the genetic variations that will
result from a cross.
3. Each trait has two genes- one from
the mother and one from the father.
4. Alleles can be homozygous – having
the same traits.
5. Alleles can be heterozygous- having
6. Physical characteristics are called
7. Genetic make up is the genotype.
III. Exploring Mendalian
A. Independent assortment
1. Genes segregate independently.
2. The principle of independent assortment
states that genes for different traits can
segregate independently during the formation
3. Independent assortment helps account for
the many genetic variations observed in
plants, animals and other organisms.
B. A summary of Mendel’s
1. Genes are passed from parent to
2. Some forms of a gene may be
dominant and others recessive.
3. In most sexually producing organisms,
each adult has two copies of each gene- one
from each parent. These genes are
segregated from each other when gametes
4. The alleles for different genes usually
segregate independently of one another.
C. Beyond Dominance and
1. Some alleles are neither dominant
nor recessive, and many traits are
controlled by multiple alleles or multiple
2. Cases in which one allele is not
completely dominant over another are
called incomplete dominance.
a. Example: White (W) and Red (R)
is both dominate. If WW X RR the
F1 generation would be WR= pink.
3. Codominance is when both alleles
contribute to the phenotype.
Example: Feather colors
4. Many genes have more than two
alleles and are referred to have multiple
a. This means that more than two
possible alleles exist in a population.
Example: colors of rabbits see page
5. Traits that are controlled by two or
more genes are said to be polygenic
traits, which means, “having many
a. Example: eye color has many
D. Applying Mendel’s principles
1. Mendel’s principals do not only
apply to plants.
A. Chromosome number
1. Every individual has two sets of
chromosomes. One from the mother
one from the father. When the
chromosomes pair up for the same trait
they are called homologous
2. A cell that contains homologous
chromosomes (2 genes) is said to be
3. Gametes (egg /sperm) have only
one chromosome and are said to be
B. Phases of Meiosis
1. Meiosis is a process of reduction division
in which the number of chromosomes per cell
is cut in half through the separation of
homologous chromosomes in a diploid cell.
2. Meiosis I- ****The homologous
chromosomes line up BUT then they CROSS
OVER, exchanging genetic information.
3. Meiosis II- The two cells produced
by meiosis I now enter a second meiotic
division. The final product = start with
1 cell with 46 chromosomes and get 4
DIFFERENT cells each with 23
Go to Internet: www.SciLinks.org code cbn-4114 to view meiosis.
V. Linkage and gene maps
A. Gene linkage
1. Thomas Hunt Morgan research on
fruit flies led him to the principal of
2. Morgan discovered that many genes
appeared “linked” together.
3. It is the chromosomes, however,
that assort independently not individual
4. Mendel DID miss gene linkage.
5. Even though if two genes are found
on the same chromosome this does not
mean they are linked forever. Crossing
over can occur.
6. Crossing over creates genetic
7. A gene map
shows the relative
location of each
gene. See page 280