What is the chromosomal abnormality associated with Down syndrome?

What is the chromosomal abnormality associated with Down syndrome?
 
  a) an extra Y chromosome
  b) a broken branch on the Y chromosome
  c) three 21 chromosomes instead of two
  d) 24 rather than 23 pairs of chromosomes

Question 2

If only one twin has a certain disease, the twin pair is said to be
 
  a) fraternal.
  b) penetrant.
  c) karyotypic.
  d) discordant.

Question 3

What are the units that make up chromosomes?
 
  a) neurons
  b) genes
  c) loci
  d) karyotypes

Question 4

_________data examines the number of new cases of a condition while _________ data examines the frequency of occurrence of a condition.
 
  a) incidence; raw
  b) incidence; prevalence
  c) survey; incidence
  d) prevalence; incidence