Mendel and

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Chapter 10 Mendel and Meiosis
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I. Gregor Mendel
A. Mendel performed 1st experiments in
heredity
-the passing on of characteristics from parents
to offspring.
B. Mendels work founded Genetics
- the study of heredity.
1. Characteristics that are inherited are
called traits
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C. Mendel used pea plants during his
experiments.
1. Pea plants reproduce sexually.
2. Sex cells are called gametes
3. Male gamete pollen.
4. Female gamete - ovule
D. Pollination- transfer of the male pollen
grains to the female ovule.
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E. In Mendels experiments, he would
sometimes take pollen from one plant and
place it on the ovule of another plant.
1. This is called cross-pollination
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II. Mendels Monohybrid Crosses
A. Mendel crossed tall pea plants with short
plants.
1. This cross is known as a hybrid.
2. Hybrid-offspring of parents that have
different traits.
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B. Mendel's results all tall plants, F1
generation
1. F stands for son or daughter.
a. F1 First Generation
b. F2 Second Generation
C. Mendels F2 generation. Some tall, some
short
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III. Rules and Laws of Heredity
A. The rule of unit factors-two factors
control an organisms traits.
B. These factors are called Genes
1. Genes are located on chromosomes.
2. Different types of genes are called
alleles.
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Example
A pea plant could have
one allele for tallness and one for shortness
OR
two alleles for tallness or shortness.
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3. An organism receives one allele from
the male parent, and one allele from the
female parent.
C. The rule of dominance-alleles are either
dominant or recessive.
Example
In pea plants, tallness is dominant to shortness.
Shortness in this example is recessive.
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1. A tall plant can have
a. One allele for tallness and one allele
for shortness.
OR
b. Two alleles for tallness.
2. A short plant can only have two alleles
for shortness.
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D. When recording the results of crosses, we
often use the 1st letter of the genes we are
crossing.
EXAMPLE
A tall plant could have the following alleles
TT or Tt
A short plant could have the following alleles
tt
E. The law of segregation-gametes randomly
pair up.
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IV. Genotypes and Phenotypes
A. Organisms can look alike, but have
different genes.
1. The way an organism looks is known as
its phenotype
The phenotype of a tall plant is TALL
B. The combination of alleles is the genotype
1. A tall plants genotype can be TT or Tt.
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2. You can never know for sure an organisms
genotype given its phenotype.
3. An organism is homozygous if its
alleles are the same.
EXAMPLE
TT or tt
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4. An organism is heterozygous if it has
one dominant allele and one recessive allele.
EXAMPLE
Tt