In Morgan's testcross of a gray-bodied, long-winged heterozygous female Drosophila with a homozygous recessive black-bodied, vestigial-winged male, the following offspring were obtained: 965 gray body, long wing; 944 black body, vestigial wing; 206 gray body, vestigial wing; 185 black body, long wing. Focusing only on the recombinant classes (gray body, vestigial wing and black body, long wing), the numbers of offspring of each type are similar (206 and 185). What accounts for the similar number of offspring of each recombinant phenotype?
Answer: Crossing over between chromosomes is reciprocal, so whenever a recombinant chromosome of one type is produced, there's a recombinant of the opposite type that is also produced.
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In 1980, only 1 to 5% of all Staphylococcus aureus isolates were MRSA strains. Now 60 to 70% of S. aureus isolates are MRSA strains. What process is the cause of this situation?
A) stabilizing selection of humans B) directional selection of humans C) directional selection of bacteria D) diversifying selection of bacteria
In E. coli, what is the function of DNA polymerase III?
A) to unwind the DNA helix during replication B) to seal together the broken ends of DNA strands C) to add nucleotides to the end of a growing DNA strand D) to degrade damaged DNA molecules
Cnidarians have what type of skeleton?
A) They don't have a skeleton B) Exoskeleton C) Endoskeleton D) Hydrostatic skeleton
Halophiles grow equally well in the presence or absence of high salt concentrations.
Answer the following statement true (T) or false (F)