Transcript Gregor Mendel “Father of Genetics”

Gregor
Mendel
“Father of
Genetics”
3 LAWS FROM
THE 1860’S
Law of Dominance
 Every
gene has two alleles that
can code for a trait.
 One
allele is dominant,
meaning it will always show.
 One
allele is recessive,
meaning it will be masked by
the presence of the dominant
allele.
Mendel crossed two pure strains of pea plants with
purple and white flowers and discovered that the
first filial generation were all purple.
Law of Dominance
States…
 Hybrids
will always show the
dominant phenotype.
 Ex:
PP = purple
Pp = purple
pp = white
Law of Segregation
 Mendel
arrived at this
conclusion by performing
monohybrid crosses.
 These were cross-pollination
experiments with pea
plants that differed in one
trait, for example height of
pea plant.
Law of Segregation
States…

The alleles for a trait separate when
gametes are formed. These alleles can then
randomly unite at fertilization.
Anaphase I of Meiosis
Anaphase II of Meiosis
Law of Independent
Assortment

Mendel began to wonder what would
happen if he studied plants that differed in
two traits (dihybrid).

Data showed that traits produced by
dominant factors do not have to appear
together in offspring.

Ex: A green seed pod (dominant) could
appear in a white-flowering pea plant
(recessive).

In other words, dominant traits don’t have
to travel together when traits are passed
from parents to offspring.



Mendel’s law of independent assortment
applies only to traits carried on different
chromosomes, i.e.unlinked genes
independent assortment occurs as a result of
the alignment of homologues during
metaphase I, determining which maternal and
paternal chromosomes assort to each daughter
cell
each pair of alleles separates independently of
every other pair of unlinked alleles during
gamete formation
The data…

Mendel performed dihybrid crosses in plants
that were true-breeding for two traits. For
example, a plant that had green pod color
and yellow seed color was cross-pollinated
with a plant that had yellow pod color and
green seeds. In this cross, the traits for green
pod color (GG) and yellow seed color (YY)
are dominant. Yellow pod color (gg) and
green seed color (yy) are recessive. The
resulting offspring or F1 generation were all
heterozygous for green pod color and yellow
seeds (GgYy).
 After
observing the results of
the dihybrid cross, Mendel
allowed all of the F1 plants to
self-pollinate.
 He
referred to these offspring
as the F2 generation.
 Mendel
noticed a 9:3:3:1 ratio.
Law of Independent
Assortment States…
 allele
pairs separate
independently during the
formation of gametes.
Therefore, traits are
transmitted to offspring
independently of one
another.