Genetics
&
Heredity
Basics
Who was Gregor Mendel?
Who was Gregor Mendel?
• Austrian monk who studied
mathematics and science at a
monastery
– As a boy he could predict the
possible types of flowers and fruits
that would result from
crossbreeding two plants in his
father’s garden
Who was Gregor Mendel?
• Curiosity about the connection
between the color of a pea flower and
the type of seed that same plant
produced inspired him to begin
experimenting with garden peas in
1856.
• Made careful use of scientific
methods, which resulted in the first
recorded study of how traits pass
from one generation to the next.
What is GENETICS?
The study of how traits are
inherited through the
interactions of genes.
What is a GENE?
• The material that controls
which traits are expressed
in an organism
• Genes come in pairs and
offspring inherit one copy
of each gene from each
parent
Define the following terms:
• Heredity
• Allele
• Trait
Define HEREDITY
The passing of traits from
parent to offspring
Define ALLELE
• The different forms of a
trait that a gene may have
• One form of a gene
Define TRAIT
• Ways of looking, thinking,
or being
• Traits that are genetic
are passed down through
the genes from parents to
offspring
Describe RECESSIVE
• A trait that is covered over,
or dominated, by another
form of that trait and seems
to disappear
• Hidden when the other copy
of the gene contains the
dominant allele.
• A recessive allele shows up
only when there is no
dominant allele present
• Shown with a lower-case
letter
What is HOMOZYGOUS?
• Both alleles [forms of the gene]
are the same
• When offspring inherit two
dominant genes, (one dominant gene
from each parent) they are said to
be homozygous dominant
• When offspring inherit two
recessive genes, (one recessive
gene from each parent) they are
said to be homozygous recessive
What is HETEROZYGOUS?
• When alleles occur in different
forms
• When offspring inherit one
dominant gene and one recessive
gene, they are said to be
heterozygous
• Since the dominant gene will be
expressed, they are said to be
heterozygous dominant
Describe CO-DOMINANCE
• When an organism has two
different alleles for a gene that
does not follow the
dominant/recessive pattern
• The organism shows a trait that
is a blend of the traits
represented by the two alleles
• Also called INCOMPLETE
DOMINANCE
Describe CO-DOMINANCE
For example:
The gene for the color of some
flowers has one allele for red
and one for white. When both
alleles are present, neither is
dominant, and the flower color
is pink
Describe DOMINANT
• A trait that covers over,
or dominates, another
form of that trait
• Trait that always shows
up, even when only one of
the two alleles is in the
dominant form
• Shown by a capital letter
Define GENOTYPE
An organism's genetic makeup
displayed in coded letters
(uppercase for dominant and
lowercase for recessive)
Define PHENOTYPE
Outward physical appearance
and behavior of an organism
What is a PUNNETT SQUARE?
• A tool to predict the probability of
certain traits in offspring that shows
the different ways alleles can
combine
• A way to show phenotype & genotype
• A chart that shows all the possible
combinations of alleles that can
result when genes are crossed
What is a PUNNETT SQUARE?
• An uppercase letter stands for a
dominant allele
• A lowercase letter stands for
recessive alleles
Read More About Punnett
Squares Here:
http://www.borg.com/~lubehawk/p
square.htm
List the 3 Principles of
Heredity
• Traits are controlled by alleles on
chromosomes
• An allele’s effect is dominant or
recessive
• When a pair of chromosomes
separate during meiosis the
different alleles for a trait move
into separate sex cells
What is meant by
MULTIPLE ALLELES?
• A trait that is controlled by
more than two alleles is said to
be controlled by multiple alleles
• Traits controlled by multiple
alleles produce more than
three phenotypes of that trait
What is meant by MULTIPLE
ALLELES?
For Example:
The alleles for blood types in humans
are called A, B, and O
The O allele is recessive to both the A
and B alleles
What is meant by MULTIPLE
ALLELES?
When a person inherits one A
allele and one B allele for
blood type, both alleles are
expressed
The person has the blood
phenotype AB
What is meant by MULTIPLE
ALLELES?
A person with phenotype A
blood inherited an A and an
O allele (AO)
~OR~
an A and an A allele (AA)
What is meant by MULTIPLE
ALLELES?
Someone with phenotype B
blood has the genotype BB or
BO
This person inherited either a
B and an O allele
~OR~
Two B alleles
What is meant by MULTIPLE
ALLELES?
A person with phenotype O
blood has the genotype OO
What is POLYGENIC
INHERITANCE?
• Occurs when a group of gene
pairs acts together to produce a
single trait
• The effects of many allele
combinations produce a wide
variety of phenotypes
Polygenic Inheritance
Example
• Human skin color is a good example
of polygenic (multiple gene)
inheritance.
– Assume that three "dominant" capital
letter genes (A, B and C) control dark
pigmentation because more melanin is
produced.