Describe how natural selection can sometimes lead to persistence of harmful or even lethal allele include exampple

Look below.

Explanation:

This question may have made it seem like natural selection is a harmful process -- be wary of this. To understand this, you have to note something known as heterozygote advantage. All this means is that the heterozygotes, the organism that expresses both the dominant and recessive alleles, rather than the homozygotes, organisms that express both dominant or both recessive alleles, have an advantage. An example is with sickle cell disease. People heterozygous for the sickle cell trait are more resistant to malaria for some reason, whereas the homozygotes are not. Because heterozygotes (which have a harmful allele and normal allele) have the advantage, natural selection selects for this trait and favors it. This leads to the "persistence of harmful or even lethal allele[s]." Again, just because the organism has a lethal allele isn't necessary always a bad thing. :)

answer: tributaries flow into rivers.

wetland is a biome that develops when the water gets accumulated in a land exhibiting a huge depression. these form either seasonally or permanently. the water in the wetland comes from rivers, lakes, ocean, flood, rain or other sources. the wetlands includes mangroves, marshes and peatland.

tributaries flow into the rivers develops a wetland because such water will get deposited in the depression and will restrict the original flow of tributary water. hence, water with low drainage current combines with the river water.

answer : haversian

[explanation: -(compact bone is organized as parallel columns, known as haversian systems, which run lengthwise down the axis of long bones. these columns are composed of lamellae, concentric rings of bone, surrounding a central channel, or haversian canal, that contains the nerves, blood vessels, and lymphatic system of the bone)]