1 Two copies of each autosomal gene affect phenotype Mendel studied autosomal gene traits (these...

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Sex-Linked Inheritance 1

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Transcript of 1 Two copies of each autosomal gene affect phenotype Mendel studied autosomal gene traits (these...

Page 1: 1 Two copies of each autosomal gene affect phenotype Mendel studied autosomal gene traits (these genes are on autosomes), like hair texture. The “either-or”

Sex-Linked Inheritance

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Page 2: 1 Two copies of each autosomal gene affect phenotype Mendel studied autosomal gene traits (these genes are on autosomes), like hair texture. The “either-or”

Two copies of each autosomal gene affect phenotype

• Mendel studied autosomal gene traits (these genes are on autosomes), like hair texture.• The “either-or” traits that

were seen in your tutorial.• Genes found on autosomes (1-

22 for humans) = autosomal traits

• Genes found on sex chromosomes (pair 23 for humans) = sex-linked traits 2

Page 3: 1 Two copies of each autosomal gene affect phenotype Mendel studied autosomal gene traits (these genes are on autosomes), like hair texture. The “either-or”

Sex Determination• Sex determined by genes

found on the X and Y chromosome– Females: egg produced

with an X chromosome– X chromosome genes in

mammals affect many traits.

• Males: ½ sperm cells contain X; and the other ½ contain Y– Chromosome genes in

mammals are responsible for male characteristics. 3

There is a 50/50 chance of child being a boy/girl

Page 4: 1 Two copies of each autosomal gene affect phenotype Mendel studied autosomal gene traits (these genes are on autosomes), like hair texture. The “either-or”

Males & Females have Different Inheritance Patterns

– ALL of a male’s sex-linked genes are expressed.

– Males have no second copies of sex-linked genes.

– Because of this, males can NEVER be “carriers” of sex-linked traits or disorders.

– Ex: Colorblindness, Hemophilia, Muscular dystrophy

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Page 5: 1 Two copies of each autosomal gene affect phenotype Mendel studied autosomal gene traits (these genes are on autosomes), like hair texture. The “either-or”

Sex-Linked Disorders• Defined: Inherited conditions found on X

chromosome• Usually recessive• Females: XX chromosomes

XH XH = healthyXH Xh = healthy carrierXh Xh = disease

• Males: XY chromosomes

XHY = healthyXhY = disease

• Rare in women (back-up X chromosome)• Ex: Colorblindness, Hemophilia, Muscular

dystrophy

Page 6: 1 Two copies of each autosomal gene affect phenotype Mendel studied autosomal gene traits (these genes are on autosomes), like hair texture. The “either-or”

4 Sex-Linked Traits:

1. Normal Color Vision: A: 29, B: 45, C: --, D: 26

2. Red-Green Color-Blind: A: 70, B: --, C: 5, D: --

3. Red Color-blind: A: 70, B: --, C: 5, D: 6

4. Green Color-Blind: A: 70, B: --, C: 5, D: 2

Sample Colorblind Tests

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Page 7: 1 Two copies of each autosomal gene affect phenotype Mendel studied autosomal gene traits (these genes are on autosomes), like hair texture. The “either-or”

Let’s take a look at…

Sex-LinkedPunnett Squares

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Page 8: 1 Two copies of each autosomal gene affect phenotype Mendel studied autosomal gene traits (these genes are on autosomes), like hair texture. The “either-or”

Jen is a healthy carrier (XH Xh) of hemophilia and Adam has no history in his family (XH Y).

What is the probability ofgetting:

Daughter with hemophilia?0%

Carrier child?25%

Child with hemophilia?25%

Two healthy children?¾ x ¾ = 9/16 (56%)

Healthy girl Healthy boy

Healthy girl (carrier)

Disease boy

Page 9: 1 Two copies of each autosomal gene affect phenotype Mendel studied autosomal gene traits (these genes are on autosomes), like hair texture. The “either-or”

Kelly is a healthy carrier of hemophilia, but Jim suffers from the disease.

What is the probability of getting a:

Healthy son?25%

Healthy daughter?25%

Child with hemophilia?50%

Carrier child?25%

Healthy girl (carrier)

Healthy boy

Disease girl Disease boy

Page 10: 1 Two copies of each autosomal gene affect phenotype Mendel studied autosomal gene traits (these genes are on autosomes), like hair texture. The “either-or”

• If the phenotype is more common in males, the gene is likely sex-linked.

Page 11: 1 Two copies of each autosomal gene affect phenotype Mendel studied autosomal gene traits (these genes are on autosomes), like hair texture. The “either-or”

Let’s try a sex-linked problem:A man and a woman marry.

The woman is a carrier of colorblindness, an X-linked disorder.

They have 4 children, 3 boys and one girl.

Two of the boys are colorblind, and the girl is a carrier.

The carrier daughter marries a healthy man.

a)What is the probability they will have a carrier?

b)What is the probability they will have a child that is colorblind?

?

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XD Xd

XD Xd

XD Y

XD Y XD YXd YXd Y

25%

25%

XD Xd

XD

Y

XD XD XD Xd

XD Y Xd Y

Page 12: 1 Two copies of each autosomal gene affect phenotype Mendel studied autosomal gene traits (these genes are on autosomes), like hair texture. The “either-or”

REVIEW1) How are sex-linked disorders different from

autosome disorders?2) Why are sex-linked disorders more common in

males?3) Write the genotype of a heterozygous dominant

female.4) Write the genotype of a carrier female.5) Examine Kelly and Jim’s Punnett square. What are

the chances they would have three children, all of whom are healthy?


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autosomal trisomies

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