Gregor Mendel conducted experiments with pea plants to study inheritance of traits. Through crosses between true-breeding parents with contrasting traits, called hybrids, Mendel discovered that traits are determined by discrete factors, now called genes, that are passed from parents to offspring. Mendel also found that some genes, called alleles, are dominant and will be expressed over recessive alleles. By allowing hybrids to self-pollinate over multiple generations, Mendel showed that recessive alleles can be passed down and later expressed independently of dominant alleles through the process of segregation.

1. Gregor Mendel & Patterns of Inheritance
Ch. 12.1-12.2

2. The Father of Genetics
• Genetics: The scientific study of biological inheritance.
• The modern science of genetics began with the work of an Austrian scientist and
priest named Gregor Mendel

3. The Role of Fertilization
• During sexual reproduction, male and
female reproductive cells join in a
process known as fertilization to
produce a new cell.
• This happens in flowers as well –more
specifically, in peas!
• Pea flowers are normally mostly self-
pollinating, which means that sperm
fertilize egg cells from within the same
flower.
• Meaning they produced offspring with
traits identical to themselves

4. Cross Fertilization
• To learn how these traits were determined, Mendel decided to “cross” his stocks
of true-breeding plants—that is, he caused one plant to reproduce with another
plant.
• The offspring of crosses between parents with different contrasting
characteristics are called hybrids

5. Generations
•When doing genetic
crosses, we call the
original pair of plants the
P generation.
•Their offspring are called
the F1 generation.
•Subsequent generations
follow F2, F3, etc.

6. Alleles, Genes, Traits
•Gene: Segment of DNA
containing instructions for a
trait
•Allele: Alternative forms of a
gene
•Mendel’s Principle of
Dominance: Some alleles are
dominant and others are
recessive.
Homologous Chromosome

7. Segregation
•Where do the recessive
alleles go?
•To figure this out, Mendel
allowed all seven kinds of
F1 hybrids to self-
pollinate.
•This reappearance
indicated that, at some
point, the allele for yellow
pods had segregated from
the allele for green pods.

8. Side note: Punnett Squares
•Capitalized = Dominant
•Lower case = Recessive
•Genotype: Genes/Alleles (ex. Yy)
•Phenotype: Physical (ex. Pink)
Y = Pink
y = white