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Welcome to Genetics:
Unit 2 Seminar!
Please feel free to chat with your
classmates!
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Agenda
• Brief Review
• Genetics Problem
– #1, #2, 2.3, 2.5 and 3.1
• Question
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Alleles

Alleles are pairs of
genes that carry
the same traits and
are found at the
same locations on
pairs of
chromosomes.
From Father
From Mother
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Autosomal Inheritance

Dominant – only one allele of a gene necessary to
express the trait
GENES

Recessive – both alleles of a gene must be
identical to express that trait
GENES
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Genetic Terms

Homozygous Trait - Both genes for that
trait are the same.


A pea plant with two genes for tallness.
Heterozygous Trait - Both genes for that
trait are not the same.

A pea plant with one gene for tallness and one for
shortness.
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Human Molecular Genetics
• Homozygous - a diploid cell or organism carry two
identical copies of a gene
• Heterozygous - a diploid cell or organism having two
different alleles of a particular gene
heterozygous
homozygous
75%
25%
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Human Molecular Genetics
• Genotype – entire genetic constitution of an individual
cell or organism, usually with emphasis on the particular
alleles at one or more specific loci.
GENES
• Phenotype – the detectable physical and physiological
characteristics of a cell or organism determined by its
genotype; also, the specific trait associated with a
particular allele.
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Practice Problem 1
• Beak color is an autosomal trait in
chickens. Red beaks are dominant
over white beaks. The allele for red
beaks is R. The allele for white beaks
is r.
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Practice Problem 1
• Claude is a chicken that has a red beak and has
a genotype of Rr. If this chicken mates with a
white-beaked chicken named Filette, what will the
baby chickens look like? What would be their
phenotypes and genotypes?
Claude
Filette
Rr
rr
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Practice Problem 1
X
Claude
Rr
?
Filette
rr
What is their Genotype?
What is their Phenotype?
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Practice Problem 1
X
Claude
Rr
Filette
rr
Genotype is Rr
Phenotype is
white beak
50%
Genotype is rr
Phenotype is
white beak
50%
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Practice Problem 2
• John is homozygous dominant for the
T allele decides to have children with a
Jane who is homozygous recessive.
• We will say the T allele is a Tall gene:
• T = tall
• t = short
*Note: In reality, there is no tall gene.
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Practice Problem 2
• John is homozygous dominant for the T
allele decides to have children with a Jane
who is homozygous recessive. First what is
John and Jane’s genotypes?
John
Jane
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Practice Problem 2
• John is homozygous dominant for the T
allele decides to have children with a Jane
who is homozygous recessive. First what is
John and Jane’s genotypes?
John
TT
Jane
tt
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Practice Problem 2
• What will their children be like? Again,
include the children's genotypes and
phenotypes.
John
TT
X
Jane
tt
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Practice Problem 2
John and Jane’s Children
Both are tall
John Junior
Tt
Jane Junior
Tt
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Discussion Question 2.3
• A woman is affected with a
trait due to a dominant gene
that shows 50% penetrance.
What is the probability that , if
she has a child, it will be
affected?
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Incomplete
Dominance
• Incomplete dominance = the
phenotype of the
heterozygous genotype is
intermediate between the
phenotypes of the
homozygous genotypes
• Incomplete dominance is
often observed when the
phenotype is quantitative
rather than discrete
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Discussion Question 2.5
• With independent assortment,
how many different types of
gametes are possible from the
genotype K/k; L/l; M/m; P/p and in
what proportions are they
expected?
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Discussion Question 2.5
• With independent assortment, how many different
types of gametes are possible from the genotype
K/k; L/l; M/m; P/p and in what proportions are they
expected?
• Gametes – egg or sperm.
• Each gene has two possible alleles; K or k.
• Therefore, the number of possible types of
gametes are 2 X 2 X 2 X 2 = 16
• The occur at an equal frequency.
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Discussion Question 3.1
• A somatic cell has 32
chromosomes aligned at
metaphase. How many
chromosomes are present at
anaphase immediately after the
centromeres have splits?
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Fig. 3.3 Mitosis
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Questions?
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