Correlation between Sperm “Redundancy” and Chiasma Frequency

Abstract

MOST male animals produce a large number of spermatozoa, whereas their females produce a relatively small number of eggs. Classically, this has been related to dilution problems in the external fertilizing medium of the female genital tract, and to synergic effects of super-numerary sperm in dissolving egg membranes or stimulating the female tract. The wide range of sperm redundancy (from 2.0 to 2 × 10¹⁰), however, suggested that another more immediate cause may be responsible. If a multiple process during spermiogenesis regularly fails in a proportion of attempts, then the number of “perfect” sperm may only be a small proportion of the total, the total produced being related logarithmically to the number of such faulty multiple processes in the production of each sperm. For example, if half such processes are faulty, then it is to be expected that where P is the number of processes in the production of one sperm, r is the sperm redundancy, R is the sperm number divided by the zygote number for one copulation, and n is the (small) number of “perfect” sperm still required for each egg to meet the exigencies of random collision paths. It was found (Fig. 1) that for those few organisms for which both chiasma frequency and sperm redundancy have been investigated, a logarithmic correlation of the form fits the points well. This may be taken to imply that about one in three chiasmata has a result which renders the resultant sperm less than “perfect”.