Stuck Sperm Cells lining the epididymis secrete a glycoprotein (beta-defensin) that coats sperm and facilitates their passage through cervical mucus. There are two common alleles for human beta-defensin: a wild-type allele (wt) and an allele with a deletion (del). To find out if this genetic variation could affect fertility, Gary Cherr and his colleagues tested the ability of sperm from men with different genotypes to pass through a gel barrier. The barrier was designed to simulate cenrical mucus. The researchers placed sperm on one side of the gel, then used a video camera to record how many passed into the gel over time. FIGURE 41.12 illustrates their results.

FIGURE 41.12 Effect of beta defensin genotype on the ability of sperm to penetrate a gel that simulates cervical mucus. Sperm from 16 men was tested: 4wt/wt, 6wt/del, and 6 del/del.

Fresh sperm were placed on one side of the gel, and a video camera was focused on a region 2.75 mm into the gel. The number of sperm in this region was recorded at one-minute intervals for six minutes. Sperm numbers shown are averages. Bars indicate range.

After four minutes, how many sperm from men with a wild-type allele were in the camera's view an average?

To determine: The number of sperms from men with a wild-type allele were in the camera’s view on average.

Introduction: The epididymis is a part of the male reproductive system. Through the epididymis, the sperms travel from the testis to the vas deferens.

An experiment was performed by researcher GC and colleagues about the effect of beta-defensin genotype on the ability of sperm to penetrate a gel that can stimulate cervical mucus. The cells of the epididymis secrete a beta-defensin protein that aids the sperms to pass through the cervical mucus of the female. The research team conducted an experiment to check whether the beta-defensin has any role in fertility. One allele of the gene coding for the beta-defensin was wild-type and the other allele was a mutated one. A barrier similar to cervical mucus was created in the form of a gel. The sperms were placed at one end of the gel and a video was recorded to check how many sperms with wild-type and mutated gene passed into the gel in the course of time.

A graph was plotted for time (minutes) on the X-axis and the number of sperms on the Y-axis for both the alleles of the beta-defensin gene.

Based on the values in the graph in Fig. 41.12, post four minutes, the men who have sperms with wild-type allele for beta defensin protein had six sperms within the camera view on average.

On average, six sperms were within the camera view after 4 minutes.