sex-linked traits. karyotype: a picture of chromosomes

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SEX-LINKED TRAITS

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Page 1: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

SEX-LINKED TRAITS

Page 2: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

Karyotype:

a picture of chromosomes.

Page 3: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

Autosomes:

the first 22 homologous pairs of chromosomes.

• Autosomes are the same for both males and females.

Page 4: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes
Page 5: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

Sex chromosomes:

determines the sex of the individual.

• The sex chromosomes are the 23rd pair of chromosomes.

Page 6: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes
Page 8: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

XY = male

Page 9: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

Which parent determines the sex of an offspring?

DAD

Page 10: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

Why? • All moms have the genotype XX.

When egg cells are made, they will all carry a single X chromosome.

Page 11: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

• All dads have the genotype XY. When sperm cells are made, 50% will have an X chromosome and 50% will have a Y chromosome.

• Therefore, males and females are born in roughly a 50:50 ratio.

Page 12: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

SEX-LINKED TRAITS:

those traits that are controlled by genes on the X or Y chromosomes.

Page 13: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

• NOTE: The Y chromosome is much smaller than the X chromosome and only contains a few genes. Most sex-linked traits are on the X chromosome.

Page 14: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

Examples of X-linked traits:

1. Hemophilia

2. Color Blindness

3. Muscular Dystrophy

4. Icthyosis simplex (scaly skin)

Page 15: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

Hemophilia

Hemophilia- Lacking in the ability to clot blood– There is a gene on

the “X” chromosome that control blood clotting

– People who have hemophilia are missing the protein to clot blood

– They can bleed to death by minor cut.

Page 16: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

In humans, hemophilia is a sex-linked trait. Having hemophilia is recessive (Xh) to being normal (XH). The heterozygous female is called a carrier. Cross a carrier female with a normal male.

XHXh X _____

Page 17: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

In humans, hemophilia is a sex-linked trait. Having hemophilia is recessive (Xh) to being normal (XH). The heterozygous female is called a carrier. Cross a carrier female with a normal male.

XHXh X XHY

Page 18: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

XH Xh

XH

Y

Page 19: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

XH Xh

XH XHXH

Y

Page 20: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

XH Xh

XH XHXH XHXh

Y

Page 21: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

XH Xh

XH XHXH XHXh

Y XHY

Page 22: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

XH Xh

XH XHXH XHXh

Y XHY XhY

Page 23: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

Genotypic ratio:

1 XHXH :1XHXh :1XHY :1XhY

Phenotypic ratio:

2 normal females: 1normal male: 1 male with hemophilia

Page 24: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

Cross a carrier female with a male with hemophilia.

XHXh X _____

Page 25: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

Cross a carrier female with a male with hemophilia.

XHXh X XhY

Page 26: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

XH Xh

Xh

Y

Page 27: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

XH Xh

Xh XHXh

Y

Page 28: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

XH Xh

Xh XHXh XhXh

Y

Page 29: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

XH Xh

Xh XHXh XhXh

Y XHY

Page 30: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

XH Xh

Xh XHXh XhXh

Y XHY XhY

Page 31: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

Genotypic ratio:

1 XHXh :1XhXh :1XHY :1XhY

Phenotypic ratio:

1 normal female: 1 female with hemophilia:1 normal male: 1 male with hemophilia

Page 32: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

Colorblindness

• A person with normal color vision sees a number seven in the circle above.

• Those who are color blind usually do not see any number at all.

Page 33: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

Colorblindness• RED-GREEN

COLORBLINDNESS:

• People with red-green color blindness see either a three or nothing at all.

• Those with normal color vision see an 8.

Page 34: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

In humans, red-green colorblindness is a sex-linked trait. People with red-green colorblindness can not tell the difference between red and green. Colorblindness is the result of a recessive allele. Cross a female with colorblindness with a male with normal vision.

XnXn X _____

Page 35: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

In humans, red-green colorblindness is a sex-linked trait. People with red-green colorblindness can not tell the difference between red and green. Colorblindness is the result of a recessive allele. Cross a female with colorblindness with a male with normal vision.

XnXn X XNY

Page 36: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

Xn Xn

XN

Y

Page 37: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

Xn Xn

XN XNXn

Y

Page 38: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

Xn Xn

XN XNXn XNXn

Y

Page 39: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

Xn Xn

XN XNXn XNXn

Y XnY

Page 40: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

Xn Xn

XN XNXn XNXn

Y XnY XnY

Page 41: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

Genotypic ratio:

2 XNXn : 2 XnY

Phenotypic ratio:

2 normal females: 2 males with colorblindness

Page 42: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

Muscular Dystrophy

- Results in weakening/loss of muscles

- Caused by defective version of gene that codes for muscle

Page 43: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

Why are sex-linked traits more common in males than in females?

• Because a male only has to inherit ONE recessive allele in order to get a sex-linked trait and a female has to inherit TWO recessive alleles in order to acquire the sex-linked trait.

Page 44: SEX-LINKED TRAITS. Karyotype: a picture of chromosomes

It is easier to inherit one recessive allele than two.

If the female only inherits one recessive allele, then they are a carrier but have the normal phenotype.