BIOLOGY REVIEWER (CHROMOSOMAL ABNORMALITIES)

Chromosomal Abnormalities

• may be due to chromosomal genetic, or environmental factors, or combination of these

• chromosomes may fail to separate properly during cell division

Karyotype

individuals complete set of chromosome

Aneuploidy

• addition or loss of one or more chromosomes

• Trisomy (2N+1), Monosomy (2N-1)

Polyploidy

• addition of chromosome sets

• Triploidy (3N), Tetraploidy (4N)

Aneuploidy

• Disjunction

• Nondisjunction

• Changes in chromosomes structure

Disjunction

normal separation of chromosomes in Meiosis I or sister chromatids in Meiosis II

Nondisjunction

• chromosomes don’t separate properly during meiosis

• problems with meiotic spindle cause errors in daughter cells

• zygote has wrong chromosome number

Changes in chromosomes structure

• Deletion

• Duplication

• Inversion

• Translocation

Deletion

removes a chromosomal segment

Duplication

repeats a segment

Inversion

reverses a segment within a chromosome

Translocation

moves a segment from one chromosome to another, non-homologous one.

Human Chromosome Disorders

• High frequency in humans

• Certain conditions are tolerated

Trisomy 21 (Down Syndrome)

• decreased muscle tone at birth

• excess skin at the nape of the neck

• flattened nose

• upward slanting eyes

• small ears and mouth

• wide, short hands with short fingers

Trisomy 18 (Edward’s Syndrome)

• mouth and jaw are small

• ears are malformed and lowset

• severe psychomotor and growth retardation are invariably present for those who survive beyond infancy

Trisomy 13 (Patau Syndrome)

• More than half of the children with this syndrome don’t survive past the first month if birth.

• Small head size

• Either small or no eyes

• 60% have cleft palate

• Extra toes or fingers

• 80% have heart disease

Trisomy 16 (Mosaic T16)

• The most common chromosomal cause of miscarriage.

• Most patients will die within the first year of life.

  Characteristics of Mosaic T16:

• Heart defects and other vascular issues

• Delayed growth

• Delayed speech and physical development

• Reproductive disorders

• Kidney problems

MONOSOMY X (45, XO): Turner Syndrome

Also known as “Gonadal dysgenesis”, it is a female chromosomal abnormality in which all or part of one of the sex chromosomes is absent (missing the Barr body, mostly 45X karyotype).
Characteristics abnormalities include:
- Gonadal dysfunction(sterility)
- Short stature
- Webbed neck
- Immature sex organs
- “Shield”- type chest (Broad and flat)

Klinefelter Syndrome: 47,XXY

• XXY male

• One in every 2000 live births

• Have male sex organs, but are sterile

• Feminine characteristics (enlarged breast, minimal facial and body hair)

• Tall

• Normal intelligence

Jacob/ XYY Syndrome (47, XYY)

• 1/1000 births

• Affected individuals are usually very tall and thin

• Many experience severe acne during adolescence

• Additional symptoms may include antisocial or behavioral problems and learning disabilities.

• Intelligence is usually normal, although IQ, on average , is 10 to 15 points lower than siblings

Metafemale/ XXX Syndrome

• A metafemale is a woman who has an extra X chromosome.

• In most cases, there will be no unusual physical features or medical problems resulting from Triple X Syndrome.

• This is because in all female cells, there is only one active X chromosome at any one time.

Cri-du-chat Syndrome

Affects on the body:

• Physical features and medical problems vary widely from child to child

• Monotone, weak, cat-like cry

• Small head(microcephally) with a round face

• High palate

• Small receding chin(micrognathia)

• Widely spaced eyes (hypertelorism)

• Folds of skin over the upper eyelid (epicanthic folds)

• Distinctive palmar creases (creases on the palms of the hands)