Module 5 Lesson 3 - 5

Lesson Summary

Meiosis is the part of our life cycle that gives rise to variety. Through the recombination of chromosomes, random assortment during separation, and random fertilization, no two people can look alike. That is true as long as the production of that organism is a result of meiosis and fertilization.

Sexual reproduction is the important step in the life cycle of most organisms where variation is introduced. Variation is the foundation of evolution as well as of understanding that the fittest will survive. In the next lesson are some examples of situations where organisms may choose to reproduce in other ways.

During this lesson, you were to concentrate on the following focusing questions:

• How does meiosis contribute to genetic variation?
• What differences exist between fraternal and identical twins?

Meiosis is the orderly separation of homologous chromosomes into haploid gametes. Through crossover events in prophase I and through independent assortment in metaphase I, meiosis ensures the production of unique gametes. When fertilization occurs later, the new offspring will have a genetic combination never before seen.

Fraternal twins result from the fertilization of two individual and different egg gametes by two individual sperm cells. Because meiosis ensures that each gamete is unique, each is genetically different.

Identical twins begin from the same sperm and egg. Early in development, the cell mass splits into two, and from there onward, each mass grows by mitosis into a full person. Because mitosis does not produce variation, these twins are genetically the same, or identical.