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The Human GenomeChapter 14

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I. Human HeredityA. Human chromosomes – There are 23

pairs of chromosomes. Half the chromosomes are from each parent.

1. Autosomal chromosomes – Chromosome numbers 1 thru 22.

2. Sex Chromosomes – chromosome pair #23. There are two options XX for female or XY for male.

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Human Chromosomes Human Karyotype

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Karyotype of Down syndrome (trisomy 21)

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Boy with Down syndrome

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Girl with Cri-du-Chat syndrome

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Nondisjunction

Trisomy

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F. Nondisjunction (not coming apart) – Causes chromosomal disorders

1. Incomplete separation of chromosomes during anaphse (I or II) during meiosis.

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F. Nondisjunction continued

2. Chromosomal Disorders: Down Syndrome – Trisomey (3

copies of a chromosome) on chromosme 21.

Turner;s Syndrome – Females with only 1 X chromosome (females are sterile).

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Nondisjunction

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Human Sex Determination

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B. Males and females are born in a roughly 50 : 50 ratio because of the way sex chromosomes separate during meiosis.

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XX XX

XY XY

X X

X

Y

Male

Female

50:50XX:XY

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C. All human egg cells carry a single X chromosome. Half of the sperm carry and X chromosome & half carry a Y chromosome.

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II. Pedigree Patterns

A pedigree chart shows the relationships within a family.

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Human TraitsA circle representsa female.

A horizontal line connecting a male and a female represents a marriage.

A shaded circle or square indicates that a person expresses the trait.

A square representsa male.

A vertical line and a bracket connect the parents to their children.

A circle or square that is not shaded indicates that a person does not express the trait.

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B. Autosomal chromosomes (#1-22)1. Dominant autosomal disorder

a.Disease is present in EVERY generation.

b.Equal chance for males or females to have the trait.

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C. Autosomal continued2. Recessive autosomal disorder

a.Disease skips generations.b.Equal chance for male or

female.

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D. Sex-linked genes1. Genes located on X & Y

chromosomes are called sex-linked genes.

2. Most sex linked traits are linked to the X chromosome

3. Males have just one X chromosome. So all X-linked alleles are expressed in males, even if they are recessive.

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The Y chromosome is much smaller than the X chromosome contains only a few genes.

Duchenne muscular dystrophy

X Chromosome

Melanoma

X-inactivation center

X-linked severe combined immunodeficiency (SCID)

Colorblindness

Hemophilia

Y Chromosome

Testis-determiningfactor

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3. Colorblindness a. Three human genes associated

with color vision are located on the X chromosome.

b. In males, a defective version of any one of these genes produces colorblindness.

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Possible Inheritance of Colorblindness Allele

Father (normal vision)