No two people are genetically identical, except for identical twins. The main source of genetic variation among humans is
a. New mutations that occurred in the preceding generation.
b. Genetic drift.
c. The reshuffling of alleles in sexual reproduction.
d. Environmental effects.

Verified step by step guidance

1. Understand the concept of genetic variation: Genetic variation refers to the differences in DNA sequences among individuals within a population. This variation is crucial for evolution and adaptation.
2. Consider the role of mutations: Mutations are changes in the DNA sequence that can introduce new genetic variations. They occur randomly and can be passed to the next generation if they occur in germ cells.
3. Explore genetic drift: Genetic drift is a mechanism of evolution that refers to random changes in allele frequencies in a population. It can lead to genetic variation but is more significant in small populations.
4. Examine the reshuffling of alleles in sexual reproduction: During sexual reproduction, alleles are reshuffled through processes like meiosis and fertilization, leading to new combinations of genes in offspring. This is a major source of genetic variation.
5. Consider environmental effects: Environmental factors can influence gene expression and phenotype but do not directly change the genetic code. They can lead to phenotypic variation but are not a primary source of genetic variation.

Key Concepts

Genetic Variation

Genetic variation refers to the differences in DNA sequences among individuals within a population. It is crucial for evolution and adaptation, as it provides the raw material for natural selection. Variation arises from mutations, gene flow, and sexual reproduction, leading to diverse traits that can affect an organism's survival and reproduction.

Mutations

Mutations are changes in the DNA sequence that can occur spontaneously or due to environmental factors. They are a primary source of genetic variation, introducing new alleles into a population. While many mutations are neutral or harmful, some can be beneficial and increase an organism's fitness, contributing to evolutionary change.

Allele Shuffling in Sexual Reproduction

During sexual reproduction, alleles are reshuffled through processes like independent assortment and crossing over during meiosis. This reshuffling creates new combinations of alleles in offspring, contributing significantly to genetic diversity. It ensures that each individual has a unique genetic makeup, except in the case of identical twins.