STANDARD: DESCRIBE TECHNIQUES OF SUCH AS CHROMOSOMAL ANALYSIS TO STUDY GENOMES

OF ORGANISMS (B.6H)

ESSENTIAL QUESTION: HOW CAN A KARYOTYPE BENEFIT PARENTS EXPECTING AN OFFSPRING.

WHAT EACH OF THE HUMAN CHROMOSOMES LOOK LIKE

KARYOTYPE: A PHOTOMICROGRAPH OF CHROMOSOMES ARRANGED ACCORDING TO A STANDARD CLASSIFICATION

IN OTHER WORDS… Chromosomes are digitally arranged so that they are matched with their homologue or “partner” chromosome.

Homologue chromosomes are the same size, shape, and carry the same genes, and one is inherited from each parent.

They are numbered according to size.

SEX DETERMINATION WITH KARYOTYPE This karyotype has

23 exact pairs, which means the person is female.

Note that #23 chromosomes are both X.

NORMAL HUMAN MALE

Note that #23 chromosomes are X and Y.

IS THIS PERSON FEMALE OR MALE?

TRISOMY 21

Abnormality shown in karyotype

Note that there are three copies of #21 chromosome.

This person has Down Syndrome.

PHOTOS OF DOWN SYNDROME PATIENTS FROM THE NATIONAL DOWN SYNDROME SOCIETY

CORRELATION BETWEEN MOTHER’S AGE AND TRISOMY 21 INCIDENCE

MONOSOMY X

Abnormality shown in karyotype

Note this person only has 1 copy of the X chromosome.

This female has Turner’s syndrome.

XXY MALE (EXTRA X)

CRI-DU-CHAT Babies with the cry of the cat syndrome have a cry

which sounds like that of a cat in distress because the infant’s larynx is improperly developed. Cri-du0chat babies are severely mentally retarded and have a small cranium. The incidences of this syndrome is 1 in 100,000 live births.

Caused by a partial deletion of chromosome 5

TRISOMY 21, ONE OF THE MOST COMMON CAUSES OF MENTAL RETARDATION IS DUE TO AN EXTRA CHROMOSOME 2`. THIS RESULTS IN A NUMBER OF CHARACTERISTIC FEATURES, SUCH AS SHORT STATURE, BROAD HANDS, STUBBY FINGERS AND TOES, AND A WIDE ROUNDED FACE. INDIVIDUALS WITH THIS SYNDROME HAVE A HIGH INCIDENCE OF HEART DEFECTS AND LUKEMIA. THE AVERAGE RISK OF HAVING A CHILD WITH DOWN’S SYNDROME IS 1 IN 750 LIVE BIRTHS. MOTHERS IN THEIR EARLY TWENTIES HAVE A RISK OF 1 IN 1,500, WOMEN OVER 35 HAVE A RISK FACTOR OF 1 IN 70.

Down’s Syndrome

EDWARD’S SYNDROME Trisomy 18 produces

severe mental retardation and a highly characteristic pattern of malformations such as elongated skull, a narrow pelvis, rocker bottom feet. Nearly all babies born with this syndrome die in early infancy. The frequency of this syndrome is 1 in 5,000 live births.

PATAU SYNDROME

This syndrome (trisomy 13) causes severely abnormal cerebral functions and virtually always leads to death in early infancy. This baby has very pronounced clefts of the lip and palate, broad nose, small cranium and nonfunctional eyes. Heart defects and severe mental retardation are also part of the clinical picture. The frequency is 1 in 15,000 live births.

TURNER SYNDROME (XO)

This is a result of nondisjunction in meiosis. These girls appear normal before puberty, but as they grow secondary sex characteristics do not develop and no ova are produced. The frequency of this syndrome is 1 in 2,500 live births.

KLINEFELTER SYNDROME (XXY)

This is a result of nondisjunction in meiosis. The frequency of this condition is 1 in 1,000 live male births. Characteristics include a tall stature and sterility. Men appear normal in other ways.

JACOBS (XYY)

A chromosome aberration which is caused by nondisjunction of the Y chromosome during the second phase of meiosis. Occurrence is 1 in 1,000 live male births. Men with this abnormality are tall and have low mental ability.

TRIPLE X

Occurs at a frequency of 1 in 1,000 female live births. No specific abnormalities are associated with this condition. The vast majority of women with this condition are normal mentally and physically and are fertile.