Transcript Genetics 101 - The Green Isle

Genetics 101:
Heredity & Probability
Essential questions:
EQ: What makes me the way I am?
EQ: What are the chances that certain
traits will be passed on to future
generations?
Scenario #1:

In humans, tongue rolling (T) is dominant. A
man that can roll his tongue (TT) is married to
a woman who cannot (tt).

Will any of their children be able to roll their
tongue?

Support your answer.
Punnett Squares: tool to help predict the possible
genotypes of the offspring.*
Tongue roller (TT)
Male gametes
Monohybrid cross
P1 generation
T
No tongue roller (tt)
t
t
Female gametes
What
are the
genotypic and
phenotypic
ratios?
F1
generation
T
Mendel’s Rule of Dominance:

When parents are
homozygous for
contrasting traits, all the
offspring will express
the dominant trait.

Mendel called the expressed
trait DOMINANT.

The trait that disappeared
was RECESSIVE.
For examples of dominant traits in pees See pg. 264
Dominant Traits in Humans
Rule of
Dominance
rules!
Scenario #2:

One of the boys from the previous case study
grows up and marries a woman who can also
roll her tongue. They have a child, however who
cannot.

What are the genotypes of the mother, father,
and children?

What are the couples chances of having a child
that can roll his tongue?
What are the genotypes of the mother, father, and
children? What are the couples chances of having
a child that can roll his tongue?
Tongue roller (___)
Male gametes
Monohybrid cross
F1 generation
Tongue roller (___)
Female gametes
F2
generation
Mendel’s First Law

Law of Segregation:
allele pairs separate or
“segregate” during
gamete formation, and
randomly unite at
fertilization.
Scenario #3:
The Dreaded Dihybrid Cross


A man (TTFF) can roll his tongue and has
freckles. He marries a woman who cannot roll
her tongue and has no freckles. (ttff)
What will the genotype of their offspring look
like?



P1 = TTFF x ttff = TtFf (F1)
All freckled, tongue rollers.
When crossing for more than one contrasting
trait, the rule of dominance is still in effect.
Scenario #4

A man heterozygous for tongue rolling and freckles
(TtFf) marries a woman who is also heterozygous
for tongue rolling and freckles.

What are their chances of having children who…




Have freckles and can roll their tongue?
Have freckles but can’t roll their tongue?
Who does not have freckles but can roll their tongue?
Who does not have freckles and can’t roll their tongue?
F1 cross: TtFf x TtFf
(Hint: Determine the number of possible gametes 1st)
TF
TF
Tf
tF
tf
Tf
tF
tf
Examples of Mendel’s Work: What are the
Genotypic and Phenotypic Ratios?
More
practice
with
punnett
squares
Mendel’s Second Law:

Law of Independent Assortment: Genes for
different traits segregate and are inherited
independently of each other.

Ex: Tongue Roller and Freckles
More practice with punnett squares
According to Mendel’s rule of
dominance, What would happen if…
X
Incomplete dominance: A cross between organisms with
different phenotypes that produces offspring with a third
phenotype. (often a blending or mixture of the two phenotypes)
Red (RR)
White (WW)
x
Pink (RW)
Black (BB)
X
White (WW)
=
Speckled (BW)
Codominance: Heterozygous genotype results in a phenotypic
expression of both dominant alleles.
Multiple Alleles: Traits controlled by more
than two alleles.

Occurs due to mutations within a population.
 Ex: Blood Types (ABO)
Genotypes
Antigens
Antibodies
Phenotypes
AA or AO
A
B
A
BB or BO
B
A
B
AB
A&B
None
AB
OO
None
A&B
O
What are the genotypic and phenotypic
possibilities for offspring if the parents are
TtFf and ttFf?
Multiple Alleles: Traits controlled by more
than two alleles within a population.

Ex: Blood Types (ABO)
Polygenic Inheritance: Inheritance pattern of a trait is
controlled by two or more genes.
History and Genetics
Timeline
Lincoln
writes Emancipation Proclamation
1863
1800
1850
1900
1865
Mendel discovers rules
of inheritance
1910
Scientists determine
that genes reside on
the chromosomes.
1964
Beatles
on TV
1950
Korean war
begins
2003
Human
Genome
project is
complete.
1950
1952
Alfred Hershey
and Martha Chase
show that DNA is
the genetic
material
2000
1953
Watson, Crick,
Wilkins, and
Franklin determine
the structure of
DNA.
1990
Human Genome
project begins