An analysis of chromosomal polymorphism in two species ofChironomus
Two populations ofChironomus dorsalis from two English localities and two ofC. riparius, one from England (my collection) and one from northern Germany (Bauer’s collection), were analysed for the incidence of inversions.
The chromosomes of different sequences are combined in individuals at random.
The two homozygotes of chromosome IV could be distinguished from the heterozygote by means of the position of the nucleolus. Analysis of the frequency of the three types showed that mating in the population was at random and that no single type was favoured at the expense of the other.
The difference in the frequency of some of the sequences found is probably accidental, due to the limited size of the populations.
No acentric or dicentric fragments were found in the meiosis of males known to have inversions. It was therefore concluded that they were situated outside the chiasma-forming regions and had in consequence no deleterious effect on fertility.
Volume 100, 2021
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