Every cell of the organism has the same DNA sequence and same genes. However, not all genes are expressed in every single cell at the same time. Only those genes necessary for a specialised function of a specialised cell are expressed in the specialised cell. For example, skin cells have some different proteins than nerve cells. Genes responsible for those "skin proteins" are activated in skin cells and are turned off in nerve cells.
<span>Random fertilization adds to the genetic variation thanks to B)Fusion of sperm and ovum, each having a unique combination of chromosomes, introduces further variation. Fertilization is a process of fusion of sperm and ovum. In a random fertilization, it is expected that sperm and ovum each have a unique combination of chromosomes. Thus, the created zygote will have a unique combination of chromosomes which introduces variation.</span>
Answer;
D. The birds have different mating seasons.
Explanation;
-Different species of birds have different mating or breeding seasons. Evolution has played a role in adjusting the timing of avian(birds) breeding seasons to maximize the number of young produced. The breeding season depends on a number of factors, for example In the temperate, subarctic, and arctic zones, the overriding factor is the availability of food. This varies across all different species of birds, irrespective of other similarities they may have.
The important thing to identify the degrees of lightness to darkness in each level.
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