Females had much larger sample size, a & c are the largest numbers on both male and female. Exam question answer: b) there has been a great deal of movement of mussels into this river from nearby lakes. What is a gene: a molecular unit of heredity in a living organism. It s made up of stretches of dna and rna that may code for a type of protein or have a function in the organism. : is a form of a gene group of genes. Different alleles may result in different traits, such as eye or flower petal color. Different alleles may gibe rise to the same trait resulting in genetic variation in alleles with little or o variation in traits. The primary source are errors in dna replication. Mutations do not occur in order to benefit the organism. Founder effects: loss of genetic variation that occurs when a new, smaller populations is established.