Here is Genetics Chapter 3, Section 1. I hope to be a usefull Topic for all of you.

1. MENDEL’S WORK
Objectives
What were the results of Mendel’s experiments
or crosses?
What controls the inheritance of traits in
organisms?

2. Mendel’s Work
 Mendel experimented with thousands
of Pea plants looking at their different
traits to understand the process of
heredity. His discoveries form the
foundation of genetics.
 Heredity –the passing of physical
characteristics from parents to
offspring
 Trait- each different form of a
characteristic
 Genetics – the study of heredity

3. Mendel’s Experiments
 Flowering Plant anatomy
 Pistil – produces the female
 sex cells or eggs
 Stamens – produce pollen which contains
the male sex cells or sperm
 Fertilization is when the egg and sperm
join forming a new organism
 In plants the pollen must reach the pistil
for fertilization to occur. This is called
pollination

4. Pollination
 Pea plants usually self-
pollinate. The pollen from their
stamens lands on the same
plants pistils.
 Mendel developed a method
to cross-pollinate pea plants.
He took pollen from one pea
plant and brushed it into the
pistil of another.

5. Crossing Pea Plants
 Mendel crossed plants with
contrasting traits
 Ex. Tall plants with short
plants
 Started with purebred plants
a purebred organism is one
who is the offspring of many
generations of that have the
same trait

6. The F1 Offspring
 Mendel crossed
purebred tall with
purebred short
Parental (P) generation
 Tall x short
 Offspring from the
cross are called F1
(filial)
 All F1 offspring were
tall

7. F2 offspring
 When F1 were full
grown, Mendel
allowed them to
self-pollinate
 F were a mix of tall
2
and short
 ¾ were tall and ¼
were short

8. Experiments with Other Traits
 Mendel crossed pea
plants with other
contrasting traits such as
seed shape, seed color,
seed coat color, etc.
 In all crosses the F1
generation had only 1
form of the trait
 In the F2 generation the
“lost” form reappeared
in ¼ of the plants.

9. Dominant and Recessive Alleles
 Mendel’s Conclusion
 factors control the
inheritance of traits in
peas.
 They exist in pairs
 The female parent
contributes one factor and
the male parent contributes
the other factor
 One factor in a pair can
mask or hide the other

10. Genes and Alleles
 Genes – factors that
control a trait
 Alleles – different forms of
a gene
 An organism traits are controlled
by the alleles it inherits from its
parents.
 Some alleles are dominant, while
others are recessive
 Dominant allele – trait always
shows
 Recessive allele –trait is hidden
whenever dominant allele is
present

11. Alleles in Mendel’s Crosses
 Stem Height Cross
 P generation tall tall x short short
 F1 generation all were tall short- Look tall
 F2 generation:
 ¼ tall tall - look tall
¼ tall short + ¼ short tall – look tall
¼ short short – look short

12. Symbols for alleles
 Letters are used to
represent alleles
 Capital letters are used
for dominant alleles
 Lowercase letters are
used for recessive alleles
 Purebred tall = TT
 Purebred short = tt
 Hybrid (one of each) =Tt

13. Significance of Mendel’s Contribution
 Before Mendel most people thought that the traits
of an individual were a blend of their 2 parents.
 If they blended the Tt plants should be medium
height
 Mendel found out that traits are determined by
individual alleles some of which are dominant
and some recessive.
 Recessive traits may seem to disappear in the
offspring only to reappear in the next generation
 Mendel’s work was not recognized during his
lifetime, but was rediscovered in 1900. He is now
considered the Father of Genetics.

14. 14