Genetic Disorders

Overview• 6 billion base pairs of DNA

~ 3 meters of DNA

• Approximately 30,000 – 70,000 genes

* Approximately 80-100,000 proteins

• These genes are spread across 24 different chromosomes

**One chromosome each from each parent, for a total of 23 pairs, or 46 chromosomes per cell**

• All normal human cells (except sex cells) have 46 chromosomes, half of which are from mom, and the other half are from dad. (23 pairs of homologous chromosomes)

• 2 sets (46) of homologous chromosomes =DIPLOID

• Pictures of chromosomes grouped in order and in pairs = Karyotype

Chromosome Number

Homologous chromosomes

Autosomal chromosomes

= non sex determining chromosomes, same shaped homologous

Sex chromosomes

Karyotype Normal male

Dark bands = Genes

Diploid!

Sex chromosomes:

X = female, Y = male

X/Y = male

X/X = female

…still sex determination

• Probability of having a boy or a girl.

X Y

X

X

Dad

Mom

X Y

X Girl Boy

X Girl Boy

XX

XX

XY

XY

50% chance for boy

50% chance for girl

Chromosomal disorders

• What if you have extra chromosome?

• What if you are missing a chromosome?

Chromosomal disorders usually:

Increase chance of having disorders, such as mental retardation, sterility, and decrease life expectancy.

Is anything wrong?

Chromosome 21 trisomy Down syndrome

Male

Trisomy 21( extra on the 21st)- Down Syndrome

• Redundant neck fold/flat occipital (back of the head)• Low set ears• Protruding/large tongue* Wide space between 1st & 2nd toes

Trisomy 13 (47,XY,+13) – Cleft Lip

Cleft Lip- a split or indentation in the lip of a newborn baby.

Sex Chromosome Abnormalities

• Turner syndrome

• Klinefelter syndrome (XXY)

• Triple X

• XYY

Is anything wrong?

X

Turner’s syndrome

Turner Syndrome• 45 Chromosomes , only one sex chromosome• The incidence is about 1 in 5000 female births

but this is only the tip of the iceberg because 99% of Turner syndrome embryos are spontaneously aborted.

• Individuals are very short, they are usually infertile.

• Characteristic body shape changes include a broad chest with widely spaced nipples and may include a webbed neck.

• IQ and lifespan are unaffected.

Is anything wrong?

XXY

Klinefelter’s syndrome

• Klinefelter Syndrome 47,XXY*The incidence at birth is about 1 in 1000 males. *Testes are small and fail to produce normal levels of testosterone which leads to breast growth in about 40% of cases and to poorly developed secondary sexual characteristics.

*Males are sterile.

*These males are taller and thinner than average and generally have a slight reduction in IQ (10-15 points below sibs). Many Kleinfelter males lead a normal life.

*Very rarely more extreme forms of Kleinfelter's syndrome occurwhere the patient has 48, XXXY or even 49, XXXXY karyotype.These individuals are generally severely handicap.

XXX Syndrome

Triple X syndrome is not inherited, but usually occurs as a random event during the formation of the reproductive cells.

*There may be a growth spurt until the age of approximately eight years of age, resulting in a taller than average final height

*They often have a increased risk of learning disabilities and delayed speech and language skills.

*They have a slightly lower intelligence level than their siblings (the IQ may be ten to fifteen points lower than their siblings).

*Females with this condition are not at any increased risk for medical problems.

XXX Syndrome

XYY Syndrome

Men who have XYY's syndrome are substantially taller, tend to be wiry-built, and tend to have severe acne.

Minor birth defects -- like pectus, crooked eye, and minor outturning of the elbows, are supposed to be common in XYY's.

Color Blindness

Colorblindness• 3 human genes

associated with color vision are located on the X chromosome.

• Because males have

one X chromosome, all the genes will be expressed, even if they are recessive.