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What is an inheritance?

Something passed from one generation to the
next.
How is it determined?

Your genes from your parents!
What are some things you
inherited?
Genetics-Objectives
Describe the principle of dominance
Describe what happens during
segregation
Apply the work of Mendel to the concepts
of genes, dominance, and segregation
Review: Types of Reproduction
Sexual reproduction: two organisms
produce a new unique organism =
VARIABLITY!!!
Asexual reproduction: one organism
produces a new nearly identical organism
= no variability!
Sexual Reproduction
Since the hereditary material comes from
two parents it resembles both parents in
some ways, but is also different from both
in others.
It has all the characteristics of its species,
but at the same time has its own individual
characteristics that distinguish it from all
other members of that species.
Genetics
• The branch of biology that is concerned
with the ways in which hereditary
information is transmitted from parents
to offspring.
Gregor Mendel
An Austrian monk and father
of genetics
Performed experiments as he
maintained the monastery
garden
Performed the first scientific
study of inheritance on pea
plants (1850s-1860s)
Why Pea Plants???
1. Traits are in 2 very different forms



Flowers purple or white
seeds yellow or green
shape round or wrinkled
2. Male and female
reproductive parts are
contained in the same
flower, you can control
mating
3. It is small and grows
easily and quickly
producing many
offspring
Pea Plants
Use parts of the flowers to reproduce
 Pollen = male sex cells
form a seed
 Eggs in flower = female sex cells
Pea plants normally reproduce by self-pollination
 Pollen fertilizes flower of the same plant
 True-breeding pea plants (“pure bred”)
Would the new plants be identical or different than the
parent? Why?
}
Pea Plants
Pea plants can cross-pollinate
Pollen fertilizes flower of a different plant
 New plants have two parent plants
Infer if the new plants would be identical or
different from the parents. Why?

Mendel cross-pollinated pea plants!
Mendel’s 1st experiments
Trait = specific characteristic that varies from
one individual to another



Height (tall or short)
Seed color (green or yellow)
Seed texture (smooth or wrinkled)
Mendel crossed plants with contrasting traits



P (Parental) = original pair of plants
F1 (First Filial) = first set of offspring
(filius means “son” in Latin)
Hybrids = offspring of parents crossed with
different traits
Try to predict the results…
Mendel’s 1st results
All of the F1 hybrid offspring had the
characteristic of only one of the parents
(so it appeared that the characteristic of
the other parent had disappeared)
Mendel’s 1st conclusions
Biological inheritance is
determined by factors
passed from one generation
to the next = genes
Each gene occurred in two
contrasting forms that
produced different
characteristics = alleles
The Principle of Dominance
Some alleles are dominant
and
others are recessive
Dominant alleles are always expressed.

Represent by a capital letter. (B – Dominant
for Brown eyes)
Recessive alleles are only expressed if
both alleles are recessive.

Represented by a lower case letter (b –
recessive for blue eyes)
What happened?
If there are at least two alleles for each
trait, what happened to the other allele that
was inherited?
Did the recessive alleles disappear or
were they hiding?
Dominant vs. Recessive
An organism with a dominant allele for a
particular trait will always have that form


When will a dominant allele show up?
The characteristic almost always shows up
An organism with a recessive allele for a
particular trait will have that form only
when the dominant allele for the trait is not
present


When will a recessive allele show up?
The characteristic only shows up when the
dominant allele is not present
Mendel’s 2nd experiments
Mendel crossed the F1 hybrid plants


F1 (First Filial) = first set of offspring (hybrids)
F2 (Second Filial) = offspring of self-pollinated F1
Dominant vs. Recessive alleles


Upper case letter = dominant allele
Lower case letter = recessive allele
Principles of Dominance
Try to predict the results…
Section 11-1
P Generation
Tall
Go to
Section:
F1 Generation
Short
Tall
Tall
F2 Generation
Tall
Tall
Tall
Short
Mendel’s 2nd results
The traits controlled by the recessive
alleles reappeared! = 25% of F2 plants
There is a new combination of alleles!
How did the trait disappear and then reappear?

Mendel’s 2nd conclusions


The dominant allele masked the corresponding
recessive allele in the F1 generation
The reappearance in the F2 generation indicated
that the alleles separated during gamete (sex
cell) formation
 Each gamete contains a single copy of each
gene
 The recessive alleles can be paired up again
in the F2 generation
The Principle of Segregation
Alleles are separated
(segregated)
during
gamete (sex cell) formation.
The Law of Segregation
1. different version of genes (alleles) account
for variations in inherited characters or traits

Alleles vary in their nucleotide sequences in
genes. Ex Blue and Brown eyes, both eye color
genes just different versions
2. For each trait, organisms inherit 2 alleles,
one from each parent.
3. If two alleles differ, then one, the dominant
allele, is fully expressed while the other,
Recessive, is masked or only partially shown
4. The two alleles for each trait segregate
during gamete, sex cell, production. (Meiosis)
Concept Map
Section 11-3
Gregor
Mendel
experimented
with
Pea
plants
concluded that
“Factors”
determine
traits
Some alleles
are dominant,
and some alleles
are recessive
which is
called the
Law of
Dominance
Go to
Section:
Alleles are
separated during
gamete formation
which is
called the
Law of
Segregation