- Which of the following cannot be detected in a
developing foetus by amniocentesis?
(a) Down’s syndrome
(b) Jaundice
(c) Klinefelter’s syndrome
(d) Sex of the foetus. - Euploidy is best explained by
(a) one chromosome more than the haploid set of
chromosomes
(b) exact multiples of a haploid set of chromosomes
(c) one chromosome more than the diploid set of
chromosomes
(d) one chromosome less than the haploid set of
chromosomes. - Which is correct for Turner’s syndrome?
(a) It is a case of monosomy.
(b) It causes sterility in females.
(c) Absence of Barr body.
(d) All of the above. - Respective haploid and monoploid numbers of
chromosomes of hexaploid wheat are
(a) 21 and 42
(b) 7 and 21
(c) 21 and 7
(d) 42 and 21.
5. Due to nondisjunction of chromosomes during
spermatogenesis, sperms carry both sex chromosomes
(22A + XY) and some sperms do not carry any sex
chromosome (22A + O). If these sperms fertilize normal
eggs (22A + X), what types of genetic disorders appear
among the offsprings?
(a) Turner’s syndrome and Klinefelter’s syndrome
(b) Down’s syndrome and Klinefelter’s syndrome
(c) Down’s syndrome and Turner’s syndrome
(d) Down’s syndrome and Cri-du-chat syndrome.
6. From a diploid condition of 2n, which condition can
arise due to nondisjunction of chromosomes?
(a) 3 n (b) 5 n
(c) 2 n+1 (d) n
7. Edward’s, Patau’s, Down’s syndromes are due to
(a) change in autosomes
(b) change in sex chromosomes
(c) mutation due to malnutrition
(d) both change in sex chromosome and autosomes.
8. Addition or deletion of one or few chromosomes from
diploid set of chromosomes results in
(a) polyploidy
(b) aneuploidy
(c) euploidy
(d) none of these.
• Two opposing changes in the number and configuration
of chromosomes are of particular importance in
evolution. In centric fusion, a process, that leads to
a decrease in chromosome number, two acrocentric
chromosomes join together to produce a metacentric
chromosome.
• In dissociation, or fission, a process that leads to
an increase in chromosome number, a metacentric
(commonly large) and a small supernumerary
metacentric fragment become translocated, so that
two acrocentric or submetacentric chromosomes are
produced.
• Fusion and dissociation are the main mechanisms by
which the chromosome number can be decreased and
increased, during evolution of the majority of animals,
and in some groups of plants.
• The evolution of chromosomes in primates consists
of modifications in morphology, in the form of fusion,
fission, inversion, and reciprocal translocation.
• At present, pericentric inversion appears to be the main
structural difference between individual chromosomes
of the great apes and humans.
• It has been postulated that evolution of the human
karyotype has occurred by a series of pericentric
inversions, which permitted genetic isolation of small
breeding groups and selection of favourable gene
combinations that gave rise to Homo sapiens.
• Evolution, however, is very complex and should be
considered from the different biochemical, cytological,
genetic, ecological, and experimental aspects.
• All these methods and approaches should be used
to analyze the intricate relationships between groups
of organisms, particularly those that show marked
variations.