JOURNAL If a disorder follows an autosomal inheritance pattern, which type of chromosome is it carried on?

AUTOSOMAL & X-LINKED DISORDERS

AUTOSOMAL DISORDER

Genetic mutation is on an autosome

AUTOSOMAL DOMINANT DISEASE

A person only needs to get the abnormal gene from one parent in order to inherit the disease

AUTOSOMAL RECESSIVE DISORDER

2 copies of an abnormal gene must be present in order for the disease or trait to develop

X-LINKED DISORDERS

Affect males & females differently

Female –XX Male--XY

Females with mild or no disease symptoms that have one mutated gene on an X chromosome and a normal version of the gene on the other X chromosome are called carriers.

Carriers are always heterozygous.

X-LINKED DOMINANT DISORDER

Passed on the dominant gene through sex chromosomes

A female only needs to have one dominant allele for the disorder to be expressed

X-LINKED RECESSIVE

Passed on the recessive gene though the sex chromosomes

A female needs to have both recessive alleles for the disorder to be expressed

The most common error in meiosis occurs when homologous chromosomes fail to separate. This mistake is known as nondisjunction, which means “not coming apart.”

Nondisjunction may result in gametes with an abnormal number of chromosomes, which can lead to a disorder of chromosome numbers.

NONDISJUNCTION The failure of a chromosome to

split correctly during meiosis

Results in the production of gametes which have either more or less than the usual amount of genetic material

Monosomy—one copy of a chromosome

Trisomy—three copies of a chromosome

If two copies of an autosomal chromosome fail to separate during meiosis, an individual may be born with three copies of that chromosome.

This condition is known as a trisomy, meaning “three bodies.”

The most common form of trisomy, involving three copies of chromosome 21, is Down syndrome, which is often characterized by mild to severe mental retardation and a high frequency of certain birth defects.

Common mechanism for trisomy or monosomy

DEFECTIVE Y-CHROMOSOME Results in the person presenting a female phenotype even though they possess an XY karyotype

Lack of the second X chromosome results in infertility

SOME TYPES OF DISORDERS

1. TURNER SYNDROME

Nondisjunction of the X chromosomes can lead to a disorder known as Turner’s syndrome.

A female with Turner’s syndrome usually inherits only one X chromosome.

Women with Turner’s syndrome are sterile, which means that they are unable to reproduce. Their sex organs do not develop properly at puberty.

TURNER SYNDROME Female in appearance

Sex organs don’t develop at puberty

Person is sterile Second sex chromosome is missing

45X or 45XO ; instead of 46XX like a normal female

Most cases are not inherited; can result from an error in cell division (nondisjunction)

2.KLINEFELTER SYNDROME

In males, nondisjunction may cause Klinefelter’s syndrome, resulting from the inheritance of an extra X chromosome, which interferes with meiosis and usually prevents these individuals from reproducing.

There have been no reported instances of babies being born without an X chromosome, indicating that this chromosome contains genes that are vital for the survival and development of the embryo.

KLINEFELTER SYNDROME 47XXY Person will appear male, but is sterile

Normal male 46XY Most cases are not inherited; result from nondisjunction

3. TRISOMY 21 Aka Down Syndrome There is an extra copy of chromosome 21; there are 3 copies of chromosome 21 instead of 2

Extra chromosome only occurs on the 21st autosomal pair

Most cases are not inherited; nondisjunction

4.MUSCULAR DYSTROPHY

Genetic disorders characterized by progressive muscle wasting & weakness that begin with microscopic changes in the muscle

The person’s muscle strength declines

One Type: Usually occurs in late 30’s or 40’s

X-linked recessive pattern

5.COLORBLINDNESS Most times the person has a

different mixture of cones from the normal

People with normal color perception have three different cones: blue, red, green

Complete loss of one cone type is dichromacy

X-linked recessive pattern

6.HEMOPHILIA X-linked recessive disorder Characterized by the inability to properly form blood clots

X-linked recessive inheritance pattern

7.TAY-SACHS Manifests itself in infancy & is fatal before the age of 5

Less severe juvenile & adult forms—developmental retardation, paralysis, dementia, blindness, retinal “cherry-red” spot, Startle reaction to sound

Mapped to chromosome 15

Autosomal recessive Fatal genetic disorder that is common among Jewish & French Canadian ancestry.

8. CYSTIC FIBROSIS Autosomal recessive condition

Affects mucus & sweat glands

Mostly—lungs, pancreas, liver, intestines, sinuses, sex organs

Mucus is usually watery; keeps the linings of certain organs moist and prevents them from drying out or getting infected

In CF the abnormal gene causes mucus to become thick & sticky

Mucus builds up in the lungs & blocks the airways

Most common fatal genetic disease in the U.S.

9.HUNTINGTON’S DISEASE

Huntington’s disease is caused by a dominant allele for a protein found in brain cells.

HUNTINGTON’S DISEASE A progressive brain disorder

that causes uncontrolled movements, emotional problems, and loss of thinking ability (cognition)

Most common form—adult-onset usually appears in the 30s or 40s

Autosomal dominant An affected person usually

inherits the altered gene from one affected parent

In rare cases, an individual with Huntington’s disease does not have a parent with the disorder

10.ALBINISM Affected people have little or no pigment in their eyes, skin, or hair

Inherited altered genes that do not make the usual amounts of pigment—melanin

Autosomal Recessive When both parents carry the gene & neither of them have albinism; 25% the child will

Disease is still a mystery

Vision ProblemsPeople with albinism always have problems with vision (not correctable with eyeglasses) and many have low vision. Vision problems in albinism result from abnormal development of the retina and abnormal patterns of nerve connections between the eye and the brain. It is the presence of these eye problems that defines the diagnosis of albinism.

While most people with albinism are fair in complexion, skin or hair color is not diagnostic of albinism. People with many types of albinism need to take precautions to avoid damage to the skin caused by the sun such as wearing sunscreen lotions, hats and sun-protective clothing.

11.NEUROFIBROMATOSIS

NF A condition that causes tumors

to grow on nerve tissue, producing skin and bone abnormalities

Autosomal dominant genetic disorders

12.FRAGILE-X Most common causes of

inherited mental impairment Can range from learning

disabilities to more severe cognitive or intellectual disabilities

X-linked Dominant Pattern

13.DWARFISM A person of short stature as an adult—dwarf

Achondroplasia Causes 70% of all dwarfism Autosomal dominant Makes legs & arms short in comparison to head & trunk

14.PKU Phenylketnuria Tested for at birth Characterized by an inability

of the body to utilize the essential amino acid—phenylalanine

Autosomal recessive A person with this disorder must limit the protein in their diet

Left untreated can cause problems with brain development, leading to progressive mental retardation & seizures