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Genetics
Mendel’s Laws of Heredity
Genetics
• Heredity: passing
of characteristics
from parents to
offspring.
• Traits: the
characteristics
that are passed to
the offspring.
Genetics
• Genetics: the
study of heredity
• Gregor Mendel:
considered the
father of genetics
• Mendel worked
with peas studying
7 different
characteristics
7 traits in Mendel’s peas
Genetic Vocabulary
Gametes: male and female
sex cells
In plants:
• male gametes are pollen.
• female gametes are eggs.
Genetic Vocabulary
• Fertilization: joining of the male
and female gametes.
• Zygote: the single cell that
results from fertilization
• Pollination: transferring pollen to
the female reproductive organ.
• Gene: segment of DNA that
controls a trait.
How did Mendel do it?
• Mendel worked
carefully to
pollinate the peas.
• Mendel studied
one trait at a time.
• He worked with
true breeding
plants.
Mendel’s crosses
• Mendel crossed a
tall plant with a
short plant to
produce a hybrid.
• Hybrid: offspring
of parents with
different forms
of a trait.
Identifying Generations
• Abbreviations are
used for the
generations.
• P1 – original
parents.
• F1 – first
generation.
• F2 – second
generation.
Mendel’s Crosses
• Mendel crossed
the offspring of
the F1 with itself
to produce the F2
generation.
• For each trait the
ratio in the F2 was
the same.
Mendel’s Conclusions
• Mendel concluded that
each trait was
controlled by 2
factors.
• These factors are
genes.
• Alleles: alternate
forms of a gene.
Expressed as
different letters.
Dominant vs. Recessive
• Dominant: an allele
that will cover or mask
another trait. It is
written as a capital
letter “T”
• Recessive: trait that
can be masked by
another trait. It is
written as a lower
case “t”
Genetics
• Genotype: the
genes present in an
organism,
expressed as 2
letters.
• Phenotype: the way
an organism looks
or behaves
Homozygous
• Homozygous: an organism is
homozygous for a trait if
both alleles are the same.
• TT is homozygous dominant
• tt is homozygous recessive
Heterozygous
• Heterozygous: an organism is
heterozygous for a trait if
the 2 alleles are different.
• Tt is heterozygous for
height.
• The dominant allele will be
expressed.