Write short notes on any two of the following:
Down.s syndrome 

Explanation

Down.s syndrome was described by J Langdon Down in 1866. It occurs due to chromosomal aberration known as aneuploidy (trisomy) where individuals possess an extrachromosome number 21. Both the chromosomes of 21 position passes into a single egg due to primary non-disjunction occurring during meiosis-I or II in maturation phase of gametogenesis. Thus, the eggs have 24 chromosomes and the offspring has 47 chromosomes (45+XY in males, 45 + XX in females).
Symptoms
Individuals are short statured with small, round head and furrowed tongue and partially open mouth.
Palm is broad with chracteristic simian palm crease, hyperflexible joints.
Slow mental, physical and psychomotor development