Autosomal & Chromosomal DisordersAutosomal & Chromosomal Disorders

Human Genetic DisordersHuman Genetic Disorders There are many genetic disorders that There are many genetic disorders that

plague humans. plague humans. Some disorders are caused by a change Some disorders are caused by a change

in just one allele in a gene while others are in just one allele in a gene while others are much more complicated. much more complicated.

It is the hope of many scientists that one It is the hope of many scientists that one day, we will have the advanced technology day, we will have the advanced technology to isolate the defective genes that cause to isolate the defective genes that cause these disorders and completely remove these disorders and completely remove them from the human genome. them from the human genome.

Autosomal DisordersAutosomal Disorders Autosomal disorders involve Autosomal disorders involve

dominant, recessive, or other dominant, recessive, or other types of traits that can produce types of traits that can produce multiple abnormalities.multiple abnormalities.

These traits are found on These traits are found on chromosomes 1-22.chromosomes 1-22.

Cystic Fibrosis, Sickle Cell, and Cystic Fibrosis, Sickle Cell, and Huntington’s disease are just a Huntington’s disease are just a few examples of autosomal few examples of autosomal disorders.disorders.

Cystic Fibrosis (CF)Cystic Fibrosis (CF) Is caused by a Is caused by a recessiverecessive allele in chromosome allele in chromosome

#7.#7. Most cases of CF involve a gene missing 3 Most cases of CF involve a gene missing 3

bases in the middle of a sequence for a protein.bases in the middle of a sequence for a protein. Because of the faulty protein, cells can not Because of the faulty protein, cells can not

transport chloride ions across their membranes.transport chloride ions across their membranes. Children with CF have serious digestive Children with CF have serious digestive

problems as well as producing a thick mucus problems as well as producing a thick mucus that clogs lungs & breathing passageways.that clogs lungs & breathing passageways.

CF Animation

Sickle Cell DiseaseSickle Cell Disease Is caused by an Is caused by an incomplete/co-dominantincomplete/co-dominant gene on gene on

chromosome #11.chromosome #11. The sickle cell gene has just one DNA base different The sickle cell gene has just one DNA base different

from the normal one.from the normal one. As a result, abnormal hemoglobin is formed which can As a result, abnormal hemoglobin is formed which can

“sickle” under low levels of oxygen.“sickle” under low levels of oxygen. These sickled cells are rigid & tend to get stuck in These sickled cells are rigid & tend to get stuck in

capillaries which can damage cells, tissues & organs. capillaries which can damage cells, tissues & organs. In some cases it can be fatal. In some cases it can be fatal.

Individuals with both recessive genes are said to have Individuals with both recessive genes are said to have sickle-cell diseasesickle-cell disease. Those who are heterozygous for . Those who are heterozygous for the trait are said to have the trait are said to have sickle-cell traitsickle-cell trait. .

SCAAnimation

Inheritance of Sickle-cell Disease

Incomplete Dominance

Huntington’s Disease (HD)Huntington’s Disease (HD)

Is caused by a Is caused by a dominantdominant gene on gene on chromosome #4chromosome #4

Individuals with HD have a slightly larger Individuals with HD have a slightly larger huntingtin gene than usual. By middle-huntingtin gene than usual. By middle-age, these abnormal proteins then begin age, these abnormal proteins then begin to attack brain cells.to attack brain cells.

Affected people are irritable, depressed, Affected people are irritable, depressed, lose muscle control & eventually die.lose muscle control & eventually die.

HDAnimation

Huntington’s Disease

Other Autosomal DisordersOther Autosomal Disorders

Recessive:Recessive: Albinism Albinism (lacking skin pigment melanin)(lacking skin pigment melanin)

Phenylketonuria Phenylketonuria (PKU- can’t break done phenylalanine causing (PKU- can’t break done phenylalanine causing problems with brain development)problems with brain development)

Tay-Sachs Tay-Sachs (fatty acids accumulate in the nerve cells of the brain; (fatty acids accumulate in the nerve cells of the brain; usually fatal) usually fatal)

Dominant:Dominant: Achondroplasia Achondroplasia (dwarfism)(dwarfism)

Hypertrichosis Hypertrichosis (werewolf syndrome)(werewolf syndrome)

Chromosomal DisordersChromosomal Disorders Chromosomal disorders Chromosomal disorders

occur when homologous occur when homologous chromosomes fail to chromosomes fail to separate (separate (nondisjunction)nondisjunction) during meiosis.during meiosis.

This creates a genome with This creates a genome with either an EXTRA either an EXTRA chromosome or a MISSING chromosome or a MISSING chromosomechromosome

Nondisjunction can occur Nondisjunction can occur with any chromosome (1-with any chromosome (1-23).23).

Downs, Turner’s, and Downs, Turner’s, and Klinefelter's syndromes are Klinefelter's syndromes are just a few examples of just a few examples of chromosomal disorders.chromosomal disorders.

Downs Syndrome (DS)Downs Syndrome (DS)

Is caused by an extra of chromosome #21.Is caused by an extra of chromosome #21. Most cases of DS are trisomy 21, however there are Most cases of DS are trisomy 21, however there are

other types of DS (Mosaic and Translocation) .other types of DS (Mosaic and Translocation) . Often DS is associated with some impairment of Often DS is associated with some impairment of

cognitive ability and physical growth as well as facial cognitive ability and physical growth as well as facial appearance. appearance.

The incidence of Down syndrome is estimated at 1 per The incidence of Down syndrome is estimated at 1 per 800 to 1,000 births, although these statistics are heavily 800 to 1,000 births, although these statistics are heavily influenced by the age of the mother.influenced by the age of the mother.

Down syndrome is not generally an inherited disorder, Down syndrome is not generally an inherited disorder, (Translocation DS may be an exception). (Translocation DS may be an exception).

DSAnimation

Turner SyndromeTurner Syndrome

Is caused by a missing X chromosome, Is caused by a missing X chromosome, monosomy X, in females (XO).monosomy X, in females (XO).

In rarer cases a second X chromosome is In rarer cases a second X chromosome is present but abnormal, while others with the present but abnormal, while others with the condition have some cells with a second X and condition have some cells with a second X and other cells without it (mosaicism). other cells without it (mosaicism).

In Turner syndrome, female sexual In Turner syndrome, female sexual characteristics are present but generally characteristics are present but generally underdeveloped. underdeveloped.

Klinefelter'sKlinefelter's

Is caused by an extra X chromosome in Is caused by an extra X chromosome in males (XXY).males (XXY).

The principal effects are development of The principal effects are development of small testicles and reduced fertility.small testicles and reduced fertility.

XYY or Super-male SyndromeXYY or Super-male Syndrome

The XYY syndrome is a disorder in which a male infant is The XYY syndrome is a disorder in which a male infant is born with an extra Y chromosome.born with an extra Y chromosome.

Boys with XYY syndrome tend to be tall and have Boys with XYY syndrome tend to be tall and have difficulties with language. The IQ tends to be slightly lower difficulties with language. The IQ tends to be slightly lower than that of other family members. than that of other family members.

Most XYY males have normal testosterone levels, sexual Most XYY males have normal testosterone levels, sexual development and usually have normal fertility.development and usually have normal fertility.

The XYY syndrome was once thought to cause aggressive The XYY syndrome was once thought to cause aggressive or violent criminal behavior, but this theory has been or violent criminal behavior, but this theory has been disproved.disproved.

Some medical geneticists question whether the term Some medical geneticists question whether the term "syndrome" is appropriate for this condition because its "syndrome" is appropriate for this condition because its phenotype is normal and the vast majority of 47,XYY males phenotype is normal and the vast majority of 47,XYY males don’t know their karyotype.don’t know their karyotype.