Mendel’s Principle of
Dominance or Recessiveness
Traits found in humans
Engage
Map of X and Y Chromosomes
Explore 1
Fundamentally Genetics
You and your groups will be looking at each
other to determine whether you are dominant
or recessive for the following traits.
Tongue Rolling
Earlobes
Earbump
Often called Darwin’s Ear Bump
Dominant - Having a small bump on the
ear
Recessive - Not having the bump
Widow’s Peak
Hitchhiker’s Thumb
Polydactyly
Syndactyly Feet
Syndactyly Hands
Severe Syndactyly
Syndactyly Surgery
Cleft Chin
Clockwise Hair Whorl
Autosomal Dominant and Recessive
Huntington Disease – Dominant Disease
Cystic Fibrosis – Recessive Disease
Sickle Cell Anemia
Tay-Sach’s
PKU
Explore 2
Bugs, Bugs, Bugs
Genes for traits are encoded and arranged linearly on
structures called chromosomes found in the nuclei of
most cells. When organisms reproduce, the resulting
offspring should receive an equal number of
chromosomes from the mother and the father.
In this activity you use the chromosomes and Bug
Traits Key to determine the genotype and phenotype
of the offspring.
Exploration 3
Wisconsin Fast Plant Genetics Lab
Explore 4
Punnett Squares
You will be able to predict the outcomes of
crosses by completing this next activity.
Explain
Mendel &
The Gene Idea
Mendel and Genetics
Answer the following questions as we
explain the concepts surrounding basic
genetic
It All Began with Mendel (FYI)
Gregor Mendel was born in 1822.
Called the “Father of Genetics”
Late 1800 chromosomes and the process of
meiosis were unknown.
Mendel’s work was considered obscure and
unimportant until 1900
Walter Sutton proposed the Chromosome
Theory and people began to listen to his
ideas.
Chromosome Theory – specific genes are
located on specific chromosomes
Three Conclusions to His Research
1. Principle of Dominance
and Recessiveness
One allele in a pair may mask the
effect of the other
2. Principle of Segregation
The two alleles for a characteristic
separate during the formation
of eggs and sperm
3. Principle of Independent
Assortment
The alleles for different
characteristics are distributed
to reproductive cells
independently.
Mendelian genetics
Character
(heritable feature, i.e., fur color)
Trait
(variant for a character, i.e., brown)
True-bred
(all offspring of same variety)
Hybridization
(crossing of 2 different true-breds)
P generation (parents)
F1 generation (first filial generation)
Genetic vocabulary…….
Punnett square:
Gene: point on a chromosome
that controls the trait
Allele: an alternate form of a gene
A or a
Homozygous: identical alleles
for a character
Heterozygous: different alleles
for a gene
Phenotype: physical traits
Genotype: genetic makeup
Testcross: breeding of a
recessive homozygote X dominate
phenotype (but unknown
genotype)
How can the Chances of an Offspring’s Traits
be Determined?
BY USING A PUNNETT SQUARE
Get out your Punnett Squares Problems
In groups of two come to the board and
complete the given monohybrid
problems.
Bb X Bb
Phenotypic Ratio
3:1
Genotypic Ratio
B 1:2:1
b
B BB Bb
b Bb bb
Exploration 4
What about two traits?
Complete the second half of your Punnett
Square Problems
What about 2 Traits?
BbTt x BbTt
The Gametes contain
one of each of the
alleles. (BT).
Each of the offspring
contain four alleles
exactly like the
parents.(BbTt).
Notice the number of
possible offspring has
increased.
The phenotypic ratio
is 9:3:3:1
BbTt x BbTt
BT Bt bT bt
BT BBTT BBTt BbTT BbTt
Bt BBTt BBtt BbTt Bbtt
bT BbTT BbTt bbTT bbTt
bt BbTt Bbtt bbTt bbtt
Exceptions to Mendel’s Rule
Incomplete Dominance
The phenotype of the
heterozygote is
intermediate between
those of the two
homozygotes.
Ex) Snap Dragon
Color
Red, Pink, White
Co-dominance
Phenotype of both
homozygotes are
produced in
heterozygotes
individuals.
Both alleles are
expressed equally.
Ex)Roan Cattle
White-feathered
birds are both
homozygotes for
both B and W alleles
Multiple Alleles
Ex )Blood type
Blood type A and B are co-dominant,
while O is recessive.
Forms possible blood types of A, B, AB,
and O.
Blood Also Shows Codominance
Sex-Determination
Chromosome pairs 1-22 are autosomes
Chromosome pair 23 are sex chromosomes
They determine the sex of an individual
XX = female XY = male
Sex-Linked Inheritance
Traits that are only found on the X
chromosome
Colorblindness and Hemophilia are
examples of sex-linked traits.
These genes are recessive and found only
on the X chromosome.
Polygenic Inheritance
Inheritance pattern of
a trait that is
controlled by two or
more genes.
Gene may be on the
same chromosome or
on different
chromosomes.
Ex) Skin color and
Height
ELABORATION 1
Exceptions to the Rule
Punnet Squares: Dihybrid, Sex-Linked,
Multiple Alleles, Co-Dominance,
Incomplete Dominance
Elaboration 2
Who’s the Parents?
Upon completion of this lab, you will:
determine the ABO blood types of two sets of
parents and two newborn children
examine the genetic relationships possible
between the parents and children
match the “mixed up” children with their proper
parents.