True breeding is when nature had to do with the breeding and Mendel didn't interfere with the breeding of the plants to get a certain offspring
Answer:
Explanation:
Organisms have different forms of circulatory systems. Humans have a closed circulatory system, while many mollusks and other invertebrates have an open system. In a closed circulatory system, blood is enclosed within blood vessels.
No, the sickle-cell anemia allele won't be eliminated by natural selection.
Sickle-cell anemia trait is controlled by a single gene and the allele (S) for sickle-cell anemia is a harmful autosomal recessive.
It is caused by a mutation in the normal allele (A) for hemoglobin (a protein on red blood cells).
Heterozygotes (AS) with the sickle-cell allele are resistant to malaria, a deadly tropical disease. It is common in many African populations.
In these areas, (S) carriers have been naturally selected, because their red blood cells, containing some abnormal hemoglobin, tend to be in sickle shape when they are infected by the malarial parasite.
Therefore, they are more likely to survive and reproduce. This keeps the S allele in the gene pool.
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