Transcript 26. Genetics Intro Notes

Genetics
 Heredity- passing of traits from parent to
offspring
 Traits- hair color, eye color, height, etc.
(are like your parents)

-characteristics that are inherited
 Genetics- the study of heredity
Gregor Mendel
 Gregor Mendel- Austrian Monk (mid
1800’s) is considered the “Father of
Genetics”
 -studied pea plants (Pisum sativum) to
explain heredity
Why study pea plants?
 1. Pea plants have easy traits to identify
(32 varieties of traits, he chose 7 to
study)

ex. Flower color, seed color, seed
shape
 2. Pea plants are small, easy to grow, and
produce large number of offspring

-allowed Mendel to have something to count
(used ratios)
 Mendel’s pea plant traits he studied
Why Study Pea Plants
 3. Pea plants have the ability to selfpollinate (both male and female parts on
same flower) or cross-pollinate
Self-Pollination
 Involves having
the pollen (male
sperm) be directly
deposited on the
female section of
the flower
Cross- Pollination
 Requires the
removal of the male
stamen (makes
pollen) on 1st flower
and transferring the
pollen from a
different flower
to the first one
Mendel’s Pea Plant
Experiments
 -he studied 3 generations of pea plants
(parents, kids, grandkids)
 1. Parents had to be true breeding (pure
plants) in which the same trait is
expressed in all offspring when pea plant
is self-pollinated
 -called the parental generation (P1)
Mendel’s Pea Plant Experiments
 2. Mendel cross-pollinated 2 varieties (1
true breeding tall and 1 true breeding
short plant) from the P1 generation
 3. This produced the F1 (“filial” or
zygote/kid possibilities) generation
*It was amazing to Mendel that all of the
kids were tall and none of them were
short!
-it appeared as if the short parent had
never existed!
Mendel’s Pea Plant
Experiments
 4. He then allowed the F1 generation to selfpollinate which produced the F2 (grandkids)
generation
*He noticed that some of the grandkids were
tall and others were short (he counted them
and found that there was a 3:1 ratio of tall to
short plants in the F2 generation)
*The short trait reappeared as if from
nowhere!
Results of Mendel’s cross of true
breeding short with a true breeding tall
pea plant
Mendel saw the same results
in different traits
Mendel’s pea experiments
Mendel’s Theory of
Heredity
 1. Parents pass on units of information to
offspring . He called “traits”= genes.
 -don’t pass trait directly because only the
unit is passed
 2. 1 unit from mother + 1 unit from father
 (gene in egg)
(gene in sperm)
2 units for each trait
Alleles on homologous
chromosomes
 *These alternative forms of a gene that
code for a trait are called alleles. There
are 2 alleles for each trait; 1 allele for a
trait is from mom and 1 allele is from dad.
Karyotype- Autosomal (#1-22)
vs. Sex-linked traits (#23)
Homozygous vs.
Heterozygous
 Homozygous- if the 2 alleles for a trait
are the same
 TT (homozygous dominate)
 tt (homozygous recessive)
 Heterozygous- if the 2 alleles for a trait
are different
 -Tt
Genotype
 Genotype- the allele combination an
organism has for a trait
 -ex. TT is the genotype (genetic formula)
of a tall plant that has 2 alleles for
tallness
Phenotype
 Phenotype- “physical appearance” of an
organism or the way it looks and behaves
 -determined by the genotype
 -the phenotype of a tall plant is tall
whether it is TT or Tt and the phenotype
of a short plant is short only if it is tt.
 3. The presence of an allele does not
guarantee it will be expressed.
 -Only the dominant allele is expressed in
heterozygous individuals and the
recessive allele is not expressed

Ex. a Tt individual will appear tall
Law of Segregation
 Alleles are passed from one generation
to the next by the Law of Segregation
which says that the 2 alleles (genes) for
each trait must separate when gametes
are formed.
Law of Segregation and
Meiosis
Law of Segregation
 Also, the Law of Independent
Assortment is followed which says the
pairs of alleles for different traits separate
independently of one another during
gamete formation.
 In other words the inheritance of one trait
has no influence on the inheritance of
another trait.
Law of independent
assortment