Chromosomal Aberrations

• Can be caused either by

– non-disjunction (failure of whole chromosomes to separate during meiosis)

– translocation (bits of chromosomes that are re-attached to other chromosomes).

• Individuals end up either with extra whole or bits of chromosomes or with missing whole or bits of chromosomes.

• These errors in meiosis increase in frequency with increasing maternal age (age 40 plus).

Super Female or Triple X Syndrome•Genotype is XXX (47 chromosomes, extra X, trisomy)•Females only (1 in a 1000) •Often no distinguishing phenotype (physically or mentally), especially in 1st year of life •May have: slight neuro-motor developmental delay, slight delay in speech and language, lack of co-ordination, immature or introverted behaviour, •Height usually taller than average, head may be smaller•Normal sexual development but increased chance of infertility •Academic performance varies from learning disabilities to above average

Turner’s Syndrome• Genotype is X (45 chromosomes, missing X,

monosomy)• Females only (1 in 2500) - many die before birth• Most have short stature & infertile - lack sexual

development (no ovarian development) • May have a webbed neck, arms that turn out slightly at

the elbow, and a low hairline in the back of the head, heart defects, kidney abnormalities

• May be prone to cardiovascular problems, kidney and thyroid problems, skeletal disorders such as scoliosis or dislocated hips, and hearing and ear disturbances.

• Kylie is 17 years old and has Turner's syndrome. She has competed in gymnastics for several international and national games. She began taking Hormone Replacement Therapy at the age of 14 and she is now 5' 1 1/2".

Klinefelter’s Syndrome

• Genotype is XXY (47 chromosomes, extra X, trisomy)

• Males only (1 in 700)• Testes do not grow (stay small) – infertile• Usually taller than average• Sparse body hair and small muscle mass due

to low levels of testosterone• May have delays in motor function, speech and

maturation and may have more feminine traits• Intellect can be normal or slightly below normal

• Tony was diagnosed with Klinefelter's syndrome when he was 36. It was discovered during investigations into why he was infertile. He is married and works as a purchasing manager for a health and fitness company.

Super Male or XXY Syndrome

• Genotype is XYY (47 chromosomes, extra Y, trisomy) • Males only (1 in a 1000)• Usually tall (above 6 feet), slender and generally

appear and act normal. • Produce high levels of testosterone.  During

adolescence they usually have severe facial acne and are poorly coordinated.  They are usually fertile.

• May be: antisocial and/or aggressive and may have below average intelligence/learning difficulties.

Down Syndrome• Have 1 extra copy of chromosome 21 (47 chromosomes –

trisomy 21)• Either gender equally affected (ranges from 1 in 1000 to 1 in 12

births as mother increases in age)• Have extra copies of genes genes - leads to over-expression of

the involved genes, leading to an incorrect expression of the traits

• Most have some mental retardation (degree varies widely) • Physical features include low muscle tone, flat facial features,

with a small nose, upward slant to the eyes, small skin folds on the inner corner of the eyes, small, abnormally shaped ears, single deep crease across the center of the palm, hyperflexibility, extra space between the big toe and the second toe, enlarged tongue that tends to stick out.

• Have a higher risk of having heart defects, gastroesophageal reflux disease, recurrent ear infections, obstructive sleep apnea, epilepsy, hypothyroidism or celiac disease

http://www.sciencemuseum.org.uk/exhibitions/genes/187.asp

We’ve highlighted just a few of the more common Chromosomal

Disorders….but there are many more…

Note – in the following video, “p” and “q” refer to the 2 arms of

chromosomes (chromatids)

• http://www.youtube.com/watch?v=ftEgxxd5VII