Transcript Dominant or Recessive

Mendel’s Principle of
Dominance or Recessiveness
Traits found in humans
Modified by Mrs. Snyder
January 2015
What is the relationship between DNA
and your physical appearance?
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Take a moment to think
about what you know
about DNA,
chromosomes, and
ribosomes. Write down
several ideas.
Now, look at the image to
the right.
What are genes? See page
111
What are genes?
If genes control traits, then we
need to find out how they do this.
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Two alleles exist for each gene (because
chromosomes are paired.) (page 111)
For now we will keep things simple.
The presence or absence of an allele impacts
an organism’s appearance.
The terms dominant, recessive,
homozygous, and heterozygous are
important for you to understand.
Terms defined
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Dominant – page 109
Recessive – page 109
Homozygous vs
heterozygous
How are alleles
represented?
Probability: pages
111- 113
Explore 1
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Fundamentally Genetics
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You and your groups will be looking at each
other to determine whether you are dominant
or recessive for the following traits.
More terms
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Genotype
phenotype
Tongue Rolling
Earlobes
Earbump
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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
Cleft Chin
Clockwise Hair Whorl
Here is the link to the lab we are
going to do
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Obtain a lap top when directed.
Create an excel chart
It should have 8 columns
Label as directed
Period 3 Lab: Partners –
randomly generated
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John, Rebecca
Laura, Ilana
Tae, Jessie
Alex, Gino
Kylie, Maria
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Grace, Justin
Andrew, Robert
Nia, Gianna
DJ, Cooper
You are a team of scientists. You are studying the random
distribution of traits (this occurs during meiosis) and will use your
traits as an example. One person is the “mother” and one is the
father.
Period 7 Partners –
randomly generated
You are a team of
scientists. You are
studying the random
distribution of traits
(this occurs during
meiosis) and will use
your traits as an
example. One person
is the “mother” and
one is the father.
Period 8 Partners –
randomly generated
You are a team of
scientists. You are
studying the random
distribution of traits
(this occurs during
meiosis) and will use
your traits as an
example. One person
is the “mother” and
one is the father.
Explore 2
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Punnett Squares
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You will be able to predict the outcomes of
crosses by completing this next activity.
Explain
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Mendel &
The Gene Idea
Mendel and Genetics
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Answer the following questions as we
explain the concepts surrounding basic
genetic
It All Began with Mendel (FYI)
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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
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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…….
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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?
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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
B
B
BB
b
Bb
Phenotypic Ratio
3:1
Genotypic Ratio
1:2:1
b
Bb
bb
Exploration 4
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What about two traits?
Complete the second half of your Punnett
Square Problems
What about 2 Traits?
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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
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The phenotype of the
heterozygote is
intermediate between
those of the two
homozygotes.
Ex) Snap Dragon
Color
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Red, Pink, White
Co-dominance
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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
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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
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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
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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
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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
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Who’s the Parents?
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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.
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