Question

natural selection pressures favor certain physical traits / adaptations that allow an organism to survive and reproduce. the physical manifestation of a trait is called the _ and are determined by a combinations of genes called the _.

genotype; phenotype
phenotype; genotype
mutations; genetic recombination / sexual reproduction
genetic recombination / sexual reproduction; mutations

what are the two main sources of genetic variation in organisms?

genotype; phenotype
genetic recombination / sexual reproduction; mutations

Explanation:

First Question (Natural Selection Traits)

To solve this, recall the definitions: Phenotype is the physical manifestation of a trait (like appearance, behavior), and genotype is the genetic makeup (combination of genes) that determines it. So the first blank is phenotype (physical trait), second is genotype (gene combination). The option with "phenotype; genotype" matches.

Genetic variation in organisms mainly comes from mutations (changes in DNA) and genetic recombination (from sexual reproduction, shuffling genes). The option "genetic recombination / sexual reproduction; mutations" lists these two sources.

Answer:

B. phenotype; genotype

Second Question (Genetic Variation Sources)