Gregor Mendel conducted experiments with pea plants to study inheritance patterns. He showed that traits are inherited as discrete units and are passed to offspring independently of other traits. Through his experiments, Mendel identified three principles of heredity: 1) dominance, where one allele is expressed over the other, 2) segregation, where offspring receive one allele from each parent, and 3) independent assortment, where traits are inherited independently. Mendel's work laid the foundation for genetics and showed that heredity follows predictable statistical patterns.

1. 6.3 Mendel and Heredity
KEY CONCEPT
Mendel’s research to what we know about genetics
today
Genetics: study of inheritance
patterns and variation.
“Father of Genetics”

2. 6.3 Mendel and Heredity
Mendel’s data laid the groundwork for genetics.
• Gregor Mendel showed that traits
are inherited as discrete units.
(without knowing about DNA)
• Mendel made three key decisions
in his experiments.
– used purebred plants
– controlled breeding
– observed seven
“either-or” traits

3. 6.3 Mendel and Heredity
• Mendel used pollen to fertilize selected pea plants
Mendel controlled the
fertilization of his pea plants
by removing the male parts,
or stamens.
He then fertilized the female
part, or pistil, with pollen from
a different pea plant.
– P generation was crossed to produce F1 generation
– interrupted the self-pollination process by removing male
flower parts so he could control the traits through
pollination to create purebred plants.

4. 6.3 Mendel and Heredity
• Mendel observed patterns in the first and second
generations of his crosses.

5. 6.3 Mendel and Heredity
• Mendel drew three important conclusions
(Mendel’s Three Principles)
1. Dominant vs. Recessive
• Organisms inherit two copies of
each gene, one from each parent.
purple white
• In many cases, one allele is
dominant (or expressed) while
the other is recessive (or
masked)

6. 6.3 Mendel and Heredity
Mendel’s 3 Principles (continued)
2. Segregation
• When meiosis makes sex cells, each cell has only
one allele
3. Independent Assortment
• Each trait is passed on independent of other traits
(creates variety!)
Ex: pod color green and seed color yellow

7. 6.3 Mendel and Heredity
Basic Genetics Vocabulary
• Chromosome
– DNA in coiled form
• Gene
– Segment of DNA
– Contains code for one trait
– Occur in pairs (one from each parent)
• Allele
-Any alternative form of a gene that may occur at a
specific gene locus (point)

8. 6.3 Mendel and Heredity
Basic Genetics Vocabulary (continued)
• Genome
- all of an organism’s genetic material
• Genotype
– Genetic makeup (the letters)
– Example: GG, Gg, or gg
• Phenotype
– Physical makeup (description)
– Example: green or yellow pea
• Homozygous alleles:
– GG = homozygous dominant
– gg = homozygous recessive
• Heterozygous alleles: Gg
G = green pea
g = yellow pea

9. 6.3 Mendel and Heredity
More info on vocabulary
• Some alleles are dominant over
others
• Therefore, 2 genotypes can produce
the dominant phenotype
• Homozygous dominant (GG) &
heterozygous (Gg) both produce
green peas

10. 6.3 Mendel and Heredity
Punnett Squares
• The Punnett square predicts the probability of traits
in offspring IF you know the genotype of the
parents.

11. 6.3 Mendel and Heredity
Probability
• The chances of an event happening
• May be expressed as a ratio, fraction, decimal, or
percent
Example
• Ratio: 1:2
• Fraction: ___
• Decimal: ___
• Percent: ___

12. 6.3 Mendel and Heredity
A Monohybrid cross examines one trait.
• Example: Both parents are heterozygous
Genotypic Ratio:
Phenotypic Ratio:

13. 6.3 Mendel and Heredity
Heredity patterns can be calculated with probability.
• Probability is the likelihood that something will happen.
• Probability =
number of ways a specific event can occur
number of total possible outcomes
• The more data you
have, the closer the
actual occurrence will
be to the predicted
occurrence.

14. 6.3 Mendel and Heredity
7.2 Codominance or Incomplete
Dominance
• In some traits, neither allele is dominant
• Example: Japanese four o’clock flowers (incomplete
dominance)
white, red, pink Notation:
White Red Pink
WW RR WR (pink)
FwFw FRFR FwFR(red & white)
–for incomplete dominance phenotype is between
dominant & recessive (pink flowers)
-for codominance, both traits are expressed (flowers will
have red areas & white areas)