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Heredity and Genetics
Heredity:
 Passing of traits from parent to offspring is called
Heredity
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Genetics is the study of DNA and Heredity.
The first major contributor to Heredity was Gregor
Mendel, the “father of Genetics.”
Mendel's Work
 Mendel studied purebred pea plants in the garden of
the monastery where he lived.
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Purebred organisms produce offspring with the same
traits as their parents.
Think of purebred dogs: a German Shepard is
purebred because if it breeds with another purebred
German Shepard, the traits are predictable. Mutts
like Sakura have many breeds mixed in them, and
have many unpredictable traits.
Heredity
 Mendel noticed that there were patterns in the traits
passed from parent to offspring. He dedicated his life
studying these patterns.
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He noticed that parent tall plants (P) which mixed
with parent tall plants (P) tended to produce tall
offspring and short plants that bred with short plants
produced short offspring.
Trait versus Characteristic:
 The plants characteristic is whether it is tall or
short.
 The word trait is used to refer to the plant's height.
Heredity
 Mendel wondered what height of offspring he would
get if he crossed a tall plant (P) with a short plant (P)
Heredity
 Mendel noticed that the offspring (F1) were all as tall
as the tall plants (because tall was the dominant
gene)
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The offspring (F1) were then self-pollinated and
made a second generation (F2)
When they grew out, ¾ of the plants were tall, and ¼
of the plants were short. The recessive 'short' genes
had shown themselves again!
Heredity
 After many years of trial and error experimentation
and mathematical calculation, Mendel compiled his
findings:
Mendel's Conclusions:
 Passing of genetic information controls an organisms
traits
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These factors must exist in pairs.
One part comes from male, one part comes from
female.
One factor can hide or 'mask' the other factor
(dominant/recessive)
Today we call these 'factors' genes.
Genes
 Each plant had a gene which controlled for the
plant's height.

Alleles are the different forms of a gene.
For example, the gene that controls the plants
height has two alleles. The F1 generation of mixed
tall/short plants had 1 short allele and 1 tall allele.
Allelles
 Dominant alleles (represented with a capital letter),
block out recessive alleles (represented as a lowercase letter)
T – Tall Plant is dominant to t – Short Plant.
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There are three ways of referring to the alleles of an
organism:
TT – Homozygous Dominant
Tt – Heterozygous Dominant
tt – Homozygous Recessive
The prefix 'hetero' means different, 'homo' means the same
Think critically: Why do you think there is no
heterozygous recessive?
Allelles
 Even though there are three genotypes: TT, Tt, tt
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There are only two phenotypes: Short and Tall