Gregor Mendel conducted experiments with pea plants to study inheritance of traits from one generation to the next. He found that traits are controlled by factors, now known as genes, that exist in different forms called alleles. In monohybrid crosses, he found that one allele can be dominant over the other in the first generation, but both alleles are passed down and segregate in a 3:1 ratio in the second generation. Mendel also discovered that genes for different traits assort independently during gamete formation according to his law of independent assortment.

1. Mendel’s Laws Of Heredity
Gregor Mendel, an Austrian monk, carried out
important studies of heredity.
Characteristics that are inherited are called traits.
Mendel was the first person to succeed in
predicting how traits are transferred from one
generation to the next.
A complete explanation requires the careful study
of genetics.

2. • Mendel worked with pea plants.
• Pea plants reproduce sexually, which means
that they produce male and female sex cells,
called gametes.
• When male gamete unites with female
gamete it is called fertilization.
• Then the fertilized cell is called a zygote.
Zygote then develops in to a seed in plants
and an embryo in animals.

3. • The transfer of pollen grains from a male
reproductive organ to a female reproductive
organ in a plant is called pollination.
• Since pea plants have both organs they selfpollinate. (male and female gametes come
from the same plant)
Mendel cross pollinated tall pea plants with
short pea plants.

4. Mendel’s Monohybrid
• Mendel cross pollinated tall pea plants with
short pea plants.
• Mendel referred to the offspring of this cross
as hybrids.
• A hybrid is the offspring of parents that have
different forms of traits, such as tall and short
height.

5. Mendel’s monohybrid crosses
The first generation (F1)
(P1) selected 6 ft pea plant and crossed
with less than 2 ft pea plant.
All F1 offspring grew to be as tall as the taller
parent. In this first generation, it was as if the
shorter parent had never existed.

6. Mendel’s monohybrid crosses
The second generation (F2)
Mendel allowed the tall plants in this first
generation to self pollinate. He planted the more
than 1000 seeds.
Mendel found that 3/4 of the plants were as
tall as the tall plans in the parent and first
generations.
He also found that ¼ of the offspring were as
short as the short plants in the parent generation.

7. The second generation (F2)
In the second generation, tall and short
plants occurred in a ratio 3 tall plants to 1 short
plant.

9. The rule of unit factors
Mendel concluded that each organism has two
factors that control each of its traits. We know
that these factors are genes and that they are
located on chromosomes.
Genes exist in alternative forms. We call
these different gene forms alleles.
Mendel’s pea plants had two alleles of the
gene that determined its height.

10. The rule of unit factors
A plant could have 2 alleles for tallness, 2
alleles for shortness, or 1 allele for tallness and 1
allele for shortness.
An organism’s two alleles are located on
different copies of a chromosome- one inherited
from the female parent and one from the male
parent.

11. The rule of dominance
In F1 generation the trait for tallness was shown.
Mendel called the observed trait dominant and
the trait that disappeared recessive.
So in the case of the F1 generation, the allele for
tall plants is dominant to the allele for the short
plants.

13. The law of segregation
The law of segregation states that every individual has
two alleles of each gene and when gametes are
produced, each gamete receives one of these alleles.

14. Phenotypes and Genotypes
Phenotype- the way an organism looks and
behaves.
Genotype- the allele combination an organism
contains.
phenotype
Genotype

15. Homozygous and heterozygous
Homozygous- two alleles for the trait are the
same. (TT) homozygous dominant, (tt)
homozygous recessive.
Heterozygous- two alleles for the trait differ
from each other. (Tt) heterozygous

16. Mendel’s dihybrid cross
Di means two.
Dihybrid cross- a cross involving two different
traits.

17. Law of independent assortment
Mendel’s second for different law states that
genes for different traits-for example, seed
shape and seed color- are inherited
independently of each other. This conclusion is
known as law of independent assortment.
Genotype RrYy- the alleles R and r will separate
from each other as well as from the alleles Y and
y.

18. Punnett squares
Monohybrid

19. Punnett squares
Dihybrid