question_answer

Why are beads on string - like structures seen in the nucleus of an eukaryptic cell under electron microscope?

Or

Answer the following questions based on sex - determination

(i) Which type of sex - determination does occur in some butterflies and moths?

(ii) Why is it exactly opposite from that of cockroaches and grasshoppers?

Answer:

In eukaryotes, the nucleosome is present as the genetic content in the cells. It constitutes chromatin (thread-like structure) as repeating unit in nucleus.

Under microscopic observation, the nucleosomes in chromatin are seen as beads on string when present in its extended form.

Or

(i) ZZ-ZW type of sex-determination occurs in moths and butterflies. The females are heterogametic (ZW) and males are homogametic (ZZ).

(ii) In insects like cockroach and grasshoppers XX-XO type of sex-determination occurs.

In them, males are heterogametic (XO), i.e. one X-chromosome producing two types of sperms XX (50 %) and XO, (without X). While the 50% females are homogametic (XX).

Opposite to this in butterflies and moths females are heterogametic and males are homogametic.

Thus, it is exactly opposite from that of cockroaches and grasshoppers.