With the severe changes to natural environments, many species are coming into contact with other species from which they were once separated, and sometimes members of the different species mate and produce hybrid offspring. One example of this is the pizzly bear, a cross between a polar bear and a grizzly bear. One concern from such hybridizations is that the hybrids tend to not survive long enough to reach reproductive age, many not even completing development. What isolating mechanism is being described here?

Postzygotic isolating mechanism

Explanation:

Reproductive isolation can occur due to prezygotic or postzygotic isolating mechanism. Prezygotic mechanism prevents fertilization of gametes and can occur due to different mating behavior, different mating time period etc. Postzygotic mechanism occurs after the formation of zygote i.e. the organisms are able to mate and fertilization also occurs. However the resultant zygote may not survive. It might not survive immediately or might die before reaching the reproductive maturity. Such a situation would still come under reproductive isolation because the resultant offspring is not viable and not able to pass on the genes to the next generation.

step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.

b tumor cells have a cell wall instead of a membrane

explanation:

tumor cells different from normal cells because tumor cells have a cell wall instead of a membrane.