Download Genetics - Solon City Schools

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 self-pollinate
(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 kids)
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.
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