Bio3400
Chapter 3
Mendelian Genetics
Gregor
Mendel
chose the garden
pea
as his model system because it grows easily to maturity in one season, and can be
artificially.
Mendel examined seven visible
characteristics
(traits), each with two contrasting
, using true-breeding parental strains.
These crosses are called
since they involve a single pair of contrasting traits. These crosses are also
since the sex of the parents did not affect the outcomes.
The original
parents
are the
generation, and their offspring are the
generation. Offspring arising from
(self-fertilizing) the F
_{1}
generation are the
generation.
To explain the results of his monohybrid crosses, Mendel proposed three postulates that form the basis for Mendelian or
genetics.
Traits are inherited in
factors (genes) which exist in pairs.
One form of each unit factor is
for the trait and the other is
.
The paired unit factors
(separate) independently during gamete formation.
The
is the genetic makeup of an individual. The
is the physical expression of the genotype.
Alternative forms of a
are called
. If the two alleles for a
trait
in an individual are the same, the individual is
, otherwise the individual is
.
A
square
is a tool to analyze and predict the ratios of
and
of a monohybrid
cross.
A
with a homozygous
individual can be used to determine whether an organism displaying the
phenotype
is homozygous or heterozygous for that trait.
A
cross
involves two pairs of contrasting
traits.
Mendel proposed a
postulate from his dihybrid
crosses:
Traits
independently
during gamete formation.
Mendel's
laws
are based on probability, and simple
mathematical
and laws of
and
can be used to find various combinations in crosses.
The probability of allele
frequencies
in the
is the
of the
probabilities
of allele frequencies in the
.
The frequency probabilities of multiple allele
combinations
is the
of the frequency probabilities of the individual alleles.
A
shows a family
tree
with respect to a
given
trait,
and is a valuable tool in human genetic
studies.
Mendel's principles of independent
and independent
can be explained by the modern
theory
of
heredity
and
events
that occur during
.