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Mendel’s Laws of Heredity
I. Gregor Mendel
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Modern genetics began in the mid-1800s in an abbey garden, where
a monk named Gregor Mendel documented inheritance in peas
Used experimental method
Excellent example of the scientific method
II. Mendel’s Work
 Mendel bred pea plants to study genetics
 Generations
 Parent generation = _________
 Offspring of P generation = ____________ (F= filial)
 Offspring of F1 generation = __________ generation
III. What did Menel’s findings mean?
 ________________ = alternate form of a gene
 Example: flower color in pea plants: can be purple or white
 For each trait expressed, an organism inherits _______ alleles
o 1 from mom
o 1 from dad
IV. Dominant vs. Recessive traits
 Dominant alleles
o will ALWAYS ______________________ recessive alleles
o represented by a ____________ letter
o dominant allele is always written _________ (Pp)
 Recessive alleles
o will only show up when ________ are present (pp)
o represented by a __________________ letter
 Scientist use the same letter for the different alleles of a trait
o Flower color in pea plants
 P = purple (dominant)
 P = white (recessive)
V. Genotype vs. Phenotype
A. Genotype (genetic)
o refers to the _________________ allele combination that is
producing the phenotype
o Flower color in pea plants (PP, Pp, pp)
B. Phenotype (physical)
o refers to what you ____________________ see
o the expression of the genotype
o you can NOT always tell the genotype by looking at the
phenotype
o Flower color in pea plants (purple or white)
Genotype
Homozygous vs. Heterozygous
 Homozygous = _________________ alleles (PP, pp)

Review: What is the
process that produces
gametes?
o
___________________
o
___________________
Heterozygous = ________________ alleles (Pp)
o
__________________
What are the
abbreviations for each
generation and what do
they stand for?
If your grandparents
were the P1 generation,
what filial generation
would that make you?
If a plant has a
dominant allele for
height and a recessive
allele for height, which
allele would determine
the height of the plant?
What does the prefix –
homo mean?
What does the prefix –
hetero mean?
Explain the difference
between homozygous
and heterozygous
Phenotype
o
2 organisms can have the ________________ phenotype but
__________________ Genotypes.
How would you
determine the
phenotype of a dog?
VII. Mendel’s Laws of Heredity

1st Law of Heredity = _____________________________________
o all organisms have a pair of alleles for each trait
o each parent passes on 1 randomly selected allele for each
trait to the offspring
o the offspring will have its own pair of alleles for that trait

2nd Law of Heredity = ____________________________________
o Separate genes for separate traits are passed down
independently of one another from parents to offspring
o Example: all people with brown hair do not have blue eyes
because the traits for hair color and eye color are inherited
INDEPENDENTLY of each other
VIII. Punnett Squares
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Used to make predictions about offspring
___________________ = the percent chance to have a trait
___________________ = relationship between the number
offspring produced (3:1 purple/white)
Explain the difference
between phenotype and
genotype.
Write down a way to
help you remember
phenotype and
genotype
Practice Set-up:
In pea plants, red flower color is dominant over white.
What does the prefix –
mono mean?
a. Cross a red purebred with a white purebred.
b. give the resulting genotypes and phenotypes and
ratios for both
What is a monohybrid?
***Remember, Punnett
squares only show the
PROBABLE allele
combinations for
offspring, not what the
four offspring will
inherit.****