A) pleiotropy
B) epistatis
C) continuous variation
D) crossing over
Correct Answer: D
Solution :
The reciprocal exchange of chromosomal material between homologous chromosomes is known as crossing over. It changes the gene type in all chromosomes, thereby resulting in a genetic variability among the resulting gametes. Pleiotropy is the phenomenon, in which one gene influences more than one trait. This type of genes often show more evident effect on one trait called major effect and less evident effects on other trait called minor effect. Epistasis discovered by Bateson (1907) is the phenomenon of suppression of phenotypic expression of a gene by a non allelic gene, which shows its own effect. The gene which masks the effect is called epistatic gene while the gene, which is suppressed is called hypostatic gene. Continuous variations are produced by segregation of chromosomes at the time of gametes or spore formation, crossing over of chromosomes during meiosis and chance combination of chromosome during fertilization. This type of variations are most common. They are neither new nor acquired variations but are already present in different organisms or races of a species.
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