AIM : WHAT IS THE ORIGIN OF
HEREDITY?
Why it matters? Our understanding of
genetics, including what makes us
unique , can be traced back to
Mendel’s discoveries
Do Now : Why do you think our
traits are not identical to our
parent’s traits?
What is Heredity ?
•The passing of traits from parents
to their offspring
•Genetics is the scientific study of
heredity.
1860s: Gregor Mendel
• “Father of Genetics”
• He figured out how traits are passed on before
we knew about DNA, or chromosomes or
meiosis
Mendelstudied heredity with pea
plants
• Why pea plants?
• 1.
(was it luck?)
Small
• 2. Easy to grow
• 3. Produces large numbers of offspring
• 4. Matures quickly
• 5. Plants can self or cross fertilize
• 6. Many varieties
• 7. Each trait has two forms
• Tall/short
purple/white flowers
• green/yellow seeds
colored/white seed coat
• green/yellow seed pods
inflated/narrowed seed pod
• wrinkled/smooth seed
1.
2.
3.
4.
Vocabulary
Self-pollinate- A plant is often able to
pollinate itself because it contains both the
male and female reproductive structures.
This only requires 1 parent.
Cross-pollinate – when pollen from the
flower of one plant is carried to the flower of
another plant.
True-breeding- result of self-pollination .All
of the offspring will have the same trait as
the parent when self-pollinated
First-generation- the very first set of
offspring from two parents
Characters – physical features
that are inherited . Examples : hair
color, height, flower color.
Trait – one of the possible forms
of a character. Example : brown
hair color, tall, purple flower.
Characters and traits
To begin, Mendel allowed peas to
self-pollinate in order to create truebreeding plants
Purple
•
First Cross – First generation – F1
pure purple with pure white
Purple
X
All purple
Second Cross – Second
Generation – F2
• Cross fertilized two of the offspring of the F1 generation
purple
purple
purple
white
purple
purple
X
Mendel’s Experiments led him to
3 Laws of Inheritance
• The Law of Dominance
• The Law of Segregation
• The Law of Independent Assortment
Think-Pair-Share
1. What is the difference between Genetics and
Heredity?
2. What is the difference between a character and a
trait?
3. What id the difference between cross-pollination
and self-pollination?
AIM : How can we predict an
outcome of a genetic cross?
Do Now :
•Using your favorite letter represent
the homozygous recessive
organism.
The Law of Dominance:
• Each individual has TWO factors for each trait
known as alleles
•
Some alleles dominate over others – the dominant allele is expressed in the
offspring
Freckles
No Freckles
No dimples
Dimples
Non-roller
Tongue
roller
From Mom
From Dad
These are
alleles
Alleles are:
• Represented by a letter of the alphabet
Capital = dominant allele A
lowercase = recessive allele a
• Each allele corresponds to a gene on a
chromosome
- the alleles represent different forms of
gene
the
Law of Segregation
The two alleles for each trait separate and move into different gametes –
meiosis
• Since only one egg or one sperm will contribute to the new offspring, only
one allele for a trait is passed on
• The chance that any allele will be passed on is 50%
•
Law of Independent Assortment
•
the inheritance of alleles for one trait doesn’t affect the inheritance
of alleles for another trait
- occurs in meiosis during metaphase 1
Genotype:
•Genotype is the combination of alleles for
a particular trait expressed with letters
Examples of Genotypes :
•Homozygous dominant:
•TT - two capital letters
•Heterozygous
•Tt - one of each letter (big and small)
•Homozygous recessive
•tt - two lower case letters
Phenotype:
• Phenotype is physical expression of the genotype
Genotype
Phenotype
TT
tall plant
Tt
tall plant
(dominant allele always is expressed over
the recessive allele)
tt
short plant
(recessive trait is expressed only if there
no dominant gene)
is
If R = red, and r = white
• What is the genotype of homozygous
dominant?
• RR
• What is the heterozygous genotype?
• Rr
• What is the homozygous recessive genotype?
• rr
If R=red and r =white
•What is the phenotype of of RR?
•Red
•What is the phenotype of Rr?
•Red
•What is the phenotype of rr?
•White
If two parents are crossed (TT X tt), what
are the resulting offspring?
You can determine phenotypes using a Punnet
square.
t
t
T
T
Tt
Tt
Tt
parent
Tt
parent
Genotypes: 4 Tt
Phenotypes: 4 Tall
This is the first or parent generation
Now try on your paper a cross of two of the
offspring from the parent generation. This is called
the first generation or the F1.
T
t
T
t
TT
Tt
Tt
tt
Genotypes: 1TT: 2Tt : 1tt
Phenotypes: 3 Tall: 1 Short.
Vocabulary
Heredity
Law of Dominance
Allele
Genotype
Phenotype
Review of the Lesson
• If a character exists in two possible forms, how many different
phenotypes can you have ?
• How many different genotypes can you have?
• The offspring of self-pollinated plant is called what?