Question

a) What problems can result from each of these types of chromosome rearrangements? (SHOW WORK & EXPLAIN)

b) Give examples of human aneuploidies including which chromosome has an extra copy, the name of the resulting syndrome, symptoms, incidence and life expectancy. (SHOW WORK & EXPLAIN)

c) Define continuous characteristic, polygenic characteristic, pleiotropy and multifactorial characteristic.

Answer 1

a.

• Chromosomal rearrangements like pericentric and paracentric inversion causes evolution of new species.
• In duplication , unequal crossing over occurs which is seen in colorblindness individuals.
• Cat-eye syndrome is caused due to a duplication of chromosomes.
• Chromosome rearrangement causes congenital abnormalities.
• Cri-du-chat is a deletion of 5 p ,Wolf-Hirschhorn syndrome is deletion of 4 p. Patients with these syndromes often have parents with balanced translocations involving the chromosomes in which the child has the deletion or duplication.

2.

Trisomy 21 - extra chromosome in the 21st chromosome causing downs syndrome.

• It is the most frequently occurring chromosomal abnormality.
• Non - disjunction of chromosomes occurs.
• Symptoms include , flat facial profile, up-slanting palpebral fissures, epicanthal folds, low-set ears with a squared-off upper helix , protruding tongue, nuchal skin, single transverse palmar creases, widened gap between the 1^st and 2^nd toes.
• Other symptoms include developmental delay, hypothyroidism, congentital heart diseases.
• Life expectency is usually 50 - 60 years.

Trisomy 18- extra chromosome in 18 th chromosome. Known as Edwards syndrome.

• It is second most common disorder next to Downs syndrome.
• Infants born with Trisomy 18 are usually small at birth.
• Symptoms include , palpebral fissures , external ear variations, cleft lip or palate, and small mouth and jaw .clenched fist with index finger overlapping the third finger and 5^th finger overlapping the 4^th, small fingernails, radial defects with underdeveloped or altered thumbs, clubfeet, and rocker-bottom feet.
• Congenital heart defects - 90%
• Short sternum, open neural tube defects, kidney defects.
• Life expectancy is low, usually die short after birth.

Trisomy 13 - Patau syndrome

• It is caused by non - disjunction and translocation.
• Symptoms - holoprosencephaly, scalp defects,microphthalmia or anophthalmia
• Congenital heart defect (80%)
• Abdomenal defects include ,Omphalocele (10%), kidney defects (30%) ,
• Polydactyly.
• Life expectancy low, 6 months or less.

Turners syndrome.

• It is caused by complete absence or partial absence of sex chromosomes.
• females with Turner syndrome are short stature and gonadal dysgenesis. The majority of affected individuals are identified at birth or before puberty due to the distinctive clinical features.
• They include webbed neck, wide-spaced nipples, lymphedema of the hands and feet, nail dysplasia, short fourth metacarpal,coarctation of the aorta, renal abnormalities, and gonadal dysgenesis.
• Girls with TS typically present with short stature or delayed puberty. Intelligence is normal.Women with TS typically present with infertility.

Klinefelters syndrome.

• It is caused by 2 x and one Y chromosome.
• Females at birt have extra chromosome of Y are born as males and develop secondary female characteristics at the time of adolescence.
• They are infertile.
• Tall stature, female body shape, underdeveloped sexual characteristics.