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(2.5 points) A graduate student attempted to generate a knockout mouse line carr

ID: 276059 • Letter: #

Question

(2.5 points) A graduate student attempted to generate a knockout mouse line carrying two null alleles of a gene named Bronco. He started out by deleting one allele of the gene in mouse embryonic stem cells (mESCs) through gene targeting technique, and then he injected the correctly manipulated mESCs with Bronco genotype (confirmed by experiments) into some blastocyst embryos, which are then implanted back into a surrogated mother. The embryos were born as healthy chimeras. However, wher he tried extensively to breed those chimeras with other healthy mice, he was not able to get a FI mouse progeny that has the Bronco +/-genotype. What can you conclude from this observation?

Explanation / Answer

From the given data, it is clear that the F1 with Branco +/- genotype could not be obtained.
This suggests that gametes with Branco- alleles are not viable. So, they cannot fuse with the Branco+ egg cell. It appears that Branco+ gene is required for proper development of gametes or gamete maturation or fertilization.