The Basics of Genetics

The Basics
of Genetics
The Father of Genetics
Gregor Mendel was an Austrian
monk who conducted and recorded
the first genetics experiments in the
1800s.
 His pioneering research formed the
basis of our understanding of
genetics.

Gregor Mendel
He studied the characteristics of pea
plants and their patterns of
inheritance.
 Because of his discoveries, Mendel is
considered the Father of Genetics.

What is Heredity?
Heredity, or inheritance, is best
described as the manner in which
inheritable characteristics (TRAITS) are
passed from one generation to the next.
 It is a RANDOM genetic outcome
influenced by the genes of the
organism(s) involved in reproduction.
 Heredity, through sexual reproduction,
ensures genetic VARIATION.

What happened?

In this experiment, Mendel crossed a
green pea with a yellow pea. The next
(F1) generation of peas was 100%
green. Why was this?

Then Mendel crossed two of those F1
green peas and the next (F2)
generation produced both green and
yellow peas. Why was this?
Mendel’s Conclusions


After many experiments, Mendel
concluded that traits are passed
from one generation to the next.
He also noted some traits are
dominant while other traits are
recessive.
Since Mendel, we’ve also learned…
each inherited trait is controlled by
two alleles.
 a trait may be controlled by several
genes and may possibly be
influenced by environmental factors.
 genes that control a trait may even be
located on various chromosomes.

Incomplete Dominance

Incomplete dominance is the result of
neither allele dominating over the other.
The two alleles blend together. (Think
of coloring with yellow and blue crayons
to make green.)
Incomplete Dominance
A
classic example of incomplete
dominance is the red 4 o’clock
and the white 4 o’clock producing
pink 4 o’clocks. Neither the red
color nor the white
color dominates…
they blend to pink.
Codominance

Codominance is the result of both
alleles being equally expressed in
the offspring. (Think of a pilot and a
co-pilot working together to fly a
plane.)
Codominance

A classic example of codominance is
blood type. Both the A and B alleles
are dominant. If an organism
inherits both, they will be type AB.
Phenotype and Genotype


Phenotype is the physical trait
expressed by the gene pair.
brown eyes
blue eyes
Genotype is the allele make-up of
the gene pair.
BB Bb bb
Homozygous and Heterozygous


Homozygous - identical alleles for a
given trait Ex: TT or tt
Heterozygous – non-identical alleles
for a given trait Ex: Tt
Punnett Squares

A Punnett square is used to predict
probably genetic outcomes of both
genotypes and phenotypes of
offspring.


One parent’s genotype goes on the left
and the other parent’s genotype goes on
the top.
The inside boxes show the
probable offspring.