Sciara (gnat)

Sciara is a genus of fungus gnats that feed on decaying organic matter and fungi, and are often found in greenhouses. Their larvae are up to 6 mm long, white, slender and legless, with a black head and smooth semi-transparent skin which reveals the contents of the digestive tract.

The adult fly is small, up to 3 mm, has a dark brown body, small head and its legs and wings are comparatively long, looking like a mosquito.

Sex determination in sciara is a different mechanism. Sciara basically has 4 pairs of chromosomes 3 pairs of autosomes and one pair of allosomes. Some special chromosomes called limited chromosomes are present in certain stages.

The zygote has 3 pairs of autosomes a one or more limited chromosomes and 3 X chromosome (2 fathers’, 1 mother's).

There are 2 stages in Sciara

1) GERM LINE

Is also the gametic line where the gamete formation takes place. The no. of chromosomesduring this line is different in males and females.

i) MALES

In the formation sperms the 1st spermatocystic division is monocentric mitosis, the maternaland paternal homologous chromosomes are separated. Then few limited chromosomes are eliminatednot all of them. After this one paternal X chromosome is also eliminated. Hence male germ line(spermatogonia) cells have 3 pairs of autosomes, 2 (one maternal and one paternal) Xchromosomes and a few limited chromosomes.

ii) FEMALES

In the formation ova the 1st ovarian division is monocentric mitosis, the maternal andpaternal homologous...
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