Download SC.912.L.16.1 - G. Holmes Braddock High School

SC.912.L.16.1
Valentina Orrego
Period: 3
Gregor Mendel
Austrian monk, also known as the “father of
modern genetics”, that discovered the
basic principles of heredity.
 Mendel performed a series of experiments
in his monastery's garden using pea
plants.
 This experiment lead to the base of
modern genetics, and the study of
heredity.

Mendel’s Experiment
 Mendel
cross-pollinated pea plants,
which resulted in them having two
parents.
 He then proceeded to study 7 different
traits of pea plants, each having a
contrasting characteristic.
 The offspring of these crosses are called
First Filial generation, or F1.
Mendel’s Experiment cont.
Principle of Dominance
 Based
on the experiments Mendel
concluded that some alleles are
dominant while others are recessive.
 A dominant allele determines an
organisms appearance. It is the one that
is shown.
 A recessive allele has no noticeable
effect. It is “hidden”.
Dihybrid crosses
 Upon
his conclusions, Mendel used
probability to explain the results of his
genetic crosses.
 A dihybrid cross is a cross between two
individuals that differ in two traits.
 A punnett square is usually used to
express the dihybrid crosses.
Dihybrid Crosses
Incomplete Dominance
 There
are some exceptions to Mendel’s
principles, meaning an allele can neither
be dominant nor recessive.
 Incomplete dominance is one of these
exceptions.
 It is when an allele is not completely
dominant over another.
Incomplete dominance
 An
example is shown in the
image below. A red
and white flower
are crossed, and
the offspring
produced
ww
are pink.
Codominance


Another exception to Mendel’s principle is
codominance.
Codominance is when the phenotype of both
alleles are
expressed.
Multiple Alleles
 Genes
that have more than two alleles
are known as multiple alleles.
 The best example for these genes is
illustrated by the ABO blood Group
system.
 A is dominant to O, B is dominant to O
and A and B are co dominant.
 This results in 4 groups: A, B, O & AB.
Polygenic Inheritance
 Polygenic
Inheritance is a kind of
inheritance in which is a trait controlled
by many genes.
 Some
examples are human skin color,
height, and weight.
 About
4 different genes control skin color.
Sex-Linked inheritance




Genes located on the sex chromosomes (X
and Y chromosomes) show a pattern of
inheritance called sex- linkage.
Genes located on the X chromosome are
found in both sexes, while genes located on
the Y chromosome are only found in males.
For example, the genes corresponding to
color vision are all located on the X
chromosome.
This is the reason color blindness is more
common in males than in females.