Chromosomes

by Janine Elijah Hermoso 

What are Chromosomes?

• These are thread-like structures in the nucleus that carry genetic information.

Parts of the Chromosome:

Types of Chromosome:

Variations of Chromosome Number:

1.  POLYPLOIDY - An increase in the number of chromosome sets in a cell. 

• Triploidy - having three copies of all autosomes and three sex chromosomes.

• Tetraploidy- having four copies of all autosomes and four sex chromosomes.
  

2. ANEUPLOIDY is the gain or loss of a single chromosome

• MONOSOMY is the loss of a single chromosome
• TRISOMY is the addition one chromosome to a diploid set.

AUTOSOMAL TRISOMY DISORDERS

1.   TRISOMY 13: PATAU SYNDROME

• Involves facial malformations, eye defects, extra fingers or toes, and feet with large protruding heels.
• Parental age is the only factor related to this trisomy.
• 1 in 15,000 chance

Typical features of an infant with Trisomy 13.  A.  Midline defect with cleft lip & palate.  B.  Clenched hand with overlapping fingers.  C. Postaxial polydactyly.  D. Equinovarus deformity.  E. Punched out aplasia cutis scalp lesions.  From http://health-7.com

2.   TRISOMY 18: EDWARDS SYNDROME

• Small at birth, grow very slowly, and are mentally retarded
• Have clenched fists
• Parental age is a factor
• 1 in 11,000 births chance

Trisomy 18

3.    TRISOMY 21: DOWN SYNDROME

• Described by John Langdon Down.
• Affected individuals have a wide, flat skull, folds in the corner of the eyelids.
• They have furrowed, large tongues that cause the mouth to remain partially open.
• Physical growth, behavior, and mental development are retarded.
• 1 in 800 live births chance.

Facial features of a baby with down syndrome

ANEUPLOIDY OF SEX CHROMOSOMES

 1.    TURNER SYNDROME (FRAGILE X)

• Affected individuals are short and wide-chested.
• There is no mental retardation.
• 1 in 10,000 female birth frequency

2.     KLINEFELTER SYNDROME (XXY)

• Affected males have very low fertility and have learning disabilities or subnormal intelligence
• 1 in 1,000 male births frequency

3.     XYY SYNDROME

• Affected males are above average in height and have personality disorders like violent criminal behavior
• 1 in 1,000 male births frequency