Post on 06-Apr-2018
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Biology 122
Genetics
Objectives:
a) Sex linked traits
b) Sex Influenced traits
c) Polygenics
d) Epistasis
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Sex-linked Traits
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Definition
Sex-linked traits are traits that arecontrolled by genes on the sex
chromosomes
The X and Y chromosomes
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Are they controlled by both sex
chromosomes?
Most sex-linked traits are controlled by genes on
the X chromosome.
This is because an X chromosome is much larger
than a Y chromosome.
A few traits are controlled by genes on the Y
chromosome.
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Different Forms of Sex-linked Inheritance
There are three different forms of sex-
linked inheritance that we will beexamining:
X-linked recessiveinheritance
X-linked dominant inheritance Y-linked inheritance
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X-linked Recessive Inheritance
X-linked recessive traits are traits resulting from
a recessive allele on the X chromosome.
X-linked recessive alleles are represented by a X ,
superscript lower case letter or a plus/minus
(+/-)
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X-linked Recessive Inheritance
These traits tend to show up in males more
than females. Why?
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X-linked Recessive Inheritance
Example #1: Colorblindness
The allele that controls colorblindness isfound on the X chromosome and is
recessive .
What genotype must a female have to be
diagnosed as colorblind?
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Are you colorblind?
Normal Color Vision:
A: 29, B: 45, C: --, D: 26Red-Green Color-Blind:
A: 70, B: --, C: 5, D: --3.
Red Color-blind:
A: 70, B: --, C: 5, D: 64.
Green Color-Blind:
A: 70, B: --, C: 5, D: 2
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X-linked Recessive Inheritance
Example #2: Hemophilia Hemophilia
Hemophilia is a serious ailment in which theblood lacks a clotting factor, and therefore whenan individual is injured, they cannot stopbleeding.
Hemophilia is also controlled by recessive alleleson the X chromosome.
http://www.ygyh.org/hemo/whatisit.htmhttp://www.ygyh.org/hemo/whatisit.htm8/3/2019 #1 Sex Linked
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X-linked Dominant Inheritance
X-linked dominant traits are traits that result fromthe presence of a dominant allele on the Xchromosome.
Unlike X-linked recessive traits, females andmales both require only ONE dominant allele inorder to express the trait.
X-linked dominant traits are represented by an X,superscript capital letter or a (+)
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X-linked Dominant Inheritance
Example: Faulty Tooth Enamel and Dental
Discoloration
Individuals who have an X chromosome
that carries a dominant allele for this traitwill have dental discoloration.
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Y-linked Inheritance
Y-linked traits are controlled by alleles on
the Y chromosome
Another word for Y-linked traits is
holandric traits as they are wholly male.
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Y-linked Inheritance
An example of a Y-linked trait is . . . . .
HAIRY EARS!
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Y-linked Inheritance
All of the sons of an affected male will
display this Y-linked trait.
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A final example of Sex-linked
Traits
Eye color in fruit flies
( Drosophilia melanogaster ) Eye color is controlled by the X chromosome.
Red eyes are dominant to white.
White eyes are most common in males.
Females only display white eyes if they are homozygous
recessive for the trait.
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Fruit Flies Continued
What type of X-linked inheritance is this?
X-linked recessive Inheritance because the malesshow the trait more often that the females. Also,
the females must have two X chromosomes, both of
which carry the recessive alleles for white eye color
in order to have white eyes!