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Genetics
= Study of Heredity
Introduction
A. Heredity =
passing of characteristics
from parent to offspring
a.Trait = characteristics that
are inherited
b. Gregor Mendel =
“Father of Genetics” (1822-1884)
I. Monk, scientist, gardener,
teacher
II. Studied thousand of pea plants;
with distinct traits
III. Simplify problems; meticulous
data collection and record
keeping; think quantitatively
B. Mendel’s Discoveries
a. Rule of Unit Factor
I. Gene = segment of DNA
on a chromosome that
controls a particular trait;
exists in alternate forms
II. Allele = contrasting
form of a gene
b. Rule of Dominance
I. Dominance = trait masks or
“dominates” another trait;
represented by Capital letter
II. Recessive – trait that is masked by
dominant trait; seems to disappears;
represents by small letter
Being able to roll your tongue is a dominant trait.
II. Crosses
A. Terminology
a. Phenotype = external appearance;
how an organism looks
b. Genotype = gene combination of an organism;
it’s genetic makeup (Bb)
c. Homozygous = 2 alleles for the trait are the same:
TT or tt
d. Heterozygous = 2 alleles in the pair are different;
Tt
B. Monohybrid Crosses
= cross between individuals
that involve one pair of
contrasting traits.
a. Punnett Square = diagram
to aid in visualizing the
results of a cross.
Monohybrid Crosses (Examples)
Ex 1: Pure Tall x Pure Short
T=Tall
t=short
T
t
t
T
Tt
Tt
Tt
Tt
100% Tall
T
t
T
TT
Tt
t
Tt
tt
25% pure tall
50% hybrid tall
25% pure short
(Homozygous x Homozygous)
(Heterozygous x Heterozygous)