#1 Sex Linked

8/3/2019 #1 Sex Linked

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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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These traits tend to show up in males more

than females. Why?


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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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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.htm


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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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An example of a Y-linked trait is . . . . .

HAIRY EARS!


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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!

#1 Sex Linked

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