Answer;
Heterozygote advantage occurs when heterozygotes have a higher fitness than do both homozygotes. In frequency-dependant selection, the fitness of a phenotype declines it it becomes too common in the population.
Explanation;
The heterozygotes have both alleles, which is needed for genetic variation. Heterozygotes are essential for there to be genetic variation in a population. In other words it is when When a single copy of a disease allele doesn't result in a disease but instead is good for the person or organism that carries it, we say that allele has a heterozygote advantage. For example a sickle cell trait, which protects against malaria in heterozygotes, but causes a deadly disease in homozygotes.
-Frequency-dependent selection occurs when the fitness of a genotype depends on its frequency. It is possible for the fitness of a genotype to increase (positively frequency-dependent) or decrease (negatively frequency-dependent) as the genotype frequency in the population increases.
Chemical building blocks of life
palentology
Answer:The answer is the second option from the top: Anoxic waters create a harsh environment that does not support marine life.
Explanation: Looking at the table, the amount of dissolved oxygen water (which enables marine species to breathe underwater) at station 138 is 0.02mg/liter compared to 1.5mg/liter, much lower than at station 137. Anoxic means "lacking oxygen", which sharks need to survive. So a lack of oxygen in a particular region will limit the number of sharks able to survive or live in that region.