Chapter 15: Study Guide

Gene Duplication

A gene on a strand of DNA duplicates itself, resulting in one working gene and one that can be modified by mutation and natural selection. This contributes to evolutionary change by allowing one gene to be modified by mutation and natural selection.

Heterozygote Advantage

Both alleles have an advantage. In such situations, a heterozygous individual is likely to outperform an individual who is homozygous for any of the two conditions. This helps preserve polymorphic loci.

Sexual Recombination

During meiosis, homologous chromosomes swap DNA, which produces new combinations of alleles. This contributes to evolutionary change in a population.

Define evolution.

Evolution refers to changes in the genetic makeup of populations over time.

Define fitness. How is fitness determined?

Fitness is the ability to survive to reproductive age, find a mate, and produce offspring. The more offspring an organism produces during its lifetime, the greater its fitness. Fitness gained by reproducing offspring is referred to as individual fitness. Inclusive fitness is the fitness derived from the individual's reproductive success plus the fitness derived through the reproductive success of its relatives.

Define founder's effect.

Founder's effect is when genetic drift changes allele frequencies when a few individuals colonize a new area. (A small subset moves out to a new place.) This is equivalent to a large population reduced by a bottleneck.

Why is genetic drift more apparent in small populations?

Genetic drift is more apparent in smaller populations because in smaller populations, genetic drift can change allele frequencies. Harmful alleles may increase in frequency, or rare advantageous alleles may be lost. Therefore, it is easier to spot in a smaller population.

The basis for evolution by natural selection requires inheritable variation in a population. Explain what this statement means.

Inheritable variation refers to genes or genetic information transferring by parent to offspring. Basically, there are changes in the allele frequency of a single organism. The gene within which these changes are occurring is passed down to the organism's offspring, which is then passed down to the offspring's offspring, and so on. This is how the variation is inherited. These variations occur through mutations, which are random acts.

What is the difference between monomorphic and polymorphic?

Monomorphic means that there is only one allele at a locus with a frequency of one. A monomorphic allele is fixed. Polymorphic means that there is more than one allele at a locus.

Summarize Darwin's theory of evolution by natural selection.

More individuals are produced each generation that can survive. Phenotypic variation exists among individuals and the variation is heritable. Those individuals with heritable traits better suited to the environment will survive.

Explain the statement: 'Natural selection acts on individuals, but populations evolve.'

Mutations occur randomly in an organism. Whether these mutations are harmful or beneficial, these mutations are passed down to offspring. Evolution is defined as the changes of the genetic makeup of populations over time, and does not occur with a single organism during a life cycle. For example, humans evolved from primates over a very long period of time, much longer than the lifespan of one individual primate.

Natural selection occurs through interaction of two factors. What are they?

Natural selection occurs through variation and overproduction.

Neutral Mutations

Neutral mutations have no effect on the cell's functioning. This helps to maintain genetic variation by not effecting any of the cell's (including the DNA's) functioning.

Which mechanism of evolution results in adaptation to the environment?

The mechanism of evolution that results in adaptation to the environment is competition for resources.

What is the net effect of a population bottleneck?

The net effect of a population bottleneck can be genetic drift and changing allele frequencies, and can result in lower genetic variability, as well as a lower ability to adapt to a changing environment.

What is the raw material on which mechanisms of evolution act upon?

The raw material on which mechanisms of evolution act upon is variation in a trait, which is caused by mutation.

If natural selection tends to reduce variation, then how is variation preserved with the population?

Variation is preserved through gene mutations and evolution, as variations are caused by mutations, which are then carried down to the offspring of the organism holding the variation, and so on. This causes an entire population to eventually evolve. Natural selection aims to get rid of bad variations, while good variations usually stay. A beneficial allele previously paired with a deleterious allele tends to get another chance to pair with a non-deleterious allele. Mixed mating strategies also help to preserve alleles.