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Introduction to Genetics
Heredity
Every living thing – plant or animal, microbe or
human being – has a set of characteristics
inherited from its parent or parents.
Since the beginning of recorded history, people
have wanted to understand how that inheritance
is passed down from generation to generation.
Most recently however, scientists have begun to
unravel the mysteries that make each person
unique.
As a result, genetics, the scientific study of
heredity, is now at the core of a revolution in
understanding biology.
Gregor Mendel
The work of an Austrian monk named Gregor
Mendel was important to understanding
biological inheritance
Mendel carried out his work with ordinary garden
peas.
He knew that part of each plant produces pollen,
which contains the plant’s male reproductive
cells – sperm. Similarly, the female portion of
the plant produces eggs.
During sexual reproduction, male and female
reproductive cells join, a process known as
fertilization.
Gregor Mendel
Mendel’s Garden
Gregor Mendel
When Mendel took charge of the monastery
garden, he had several stocks of pea plants
These peas were true breeding, meaning that if
they were allowed to self-pollinate, they would
produce offspring identical to themselves.
Mendel wanted to produce seeds by joining
male and female reproductive cells from two
different plants.
Start taking notes
Genes and Dominance
Mendel studied seven different pea plant traits.
A trait is a specific characteristic such as seed
color or plant height, which varies from one
individual to the other.
Mendel crossed plants with each of the seven
contrasting characters and studied their
offspring.
Mendel called each original pair of parents the P
(parental) generation and their offspring the F1
generation.
Genes
From his experiments, Mendel concluded
that biological inheritance was determined
by factors that are passed down from one
generation to the next.
Today, scientists call these factors GENES
Since sexual reproducing organisms have
two parents, then they have two forms of
the same gene – one from each parent
Genes
These alternate forms of genes are called
alleles
If both alleles from each parent are the
same, then it is said to be homozygous
(dominant or recessive)
IF they are different, then it is said to be
heterozygous
Genotype vs. Phenotype
An individual’s genetic make-up is known
as the genotype
The physical characteristics resulting from
an individual’s genetic make-up is known
as the phenotype.
Summary of Mendel’s Principles
The inheritance of biological
characteristics is determined by individual
units known as genes
In cases in which two or more forms
(alleles) of the gene for a single trait exist,
some forms of the gene may be dominant
and others may be recessive.
The dominant gene is the one that is
expressed.
The End