6 6 Meiosis and Genetic Variation KEY CONCEPT

6. 6 Meiosis and Genetic Variation KEY CONCEPT Independent assortment and crossing over during meiosis result in genetic diversity.

6. 6 Meiosis and Genetic Variation Sexual reproduction creates unique combinations of genes. Sexual reproduction creates unique combination of genes and therefore increases genetic variation. There are 3 main ways sexual reproduction leads to increased genetic variation: – 1. independent assortment of chromosomes in meiosis - Meaning each chromosome lines up on the equator independently of other chromosomes. – 2. random fertilization of gametes example: in humans, a gamete can form with 223 (about 8 million) different combinations. During fertilization the total possible combinations are 223 x 223 , or 70 trillion, different combinations of chromosomes. • Unique traits may give a reproductive advantage to some organisms. Fig. 6. 1 –This image shows only a small sample of the great genetic potential for variety in the human population.

6. 6 Meiosis and Genetic Variation Crossing over during meiosis increases genetic diversity. • 3. Crossing over is the exchange of chromosome segments between homologous chromosomes. – occurs during prophase I of meiosis I – results in new combinations of genes – The farther apart two genes are located on a chromosome, the more likely they are to be separated by crossing over.

6. 6 Meiosis and Genetic Variation Summary of sources of genetic variation in eukaryotes: • 1. Independent assortment of chromosomes during of meiosis. • 2. Random fertilization. • 3. Crossing over of homologous chromosomes during prophase I of meiosis. Calculate: Fruit fly gametes each have 4 chromosomes, representing 24, or 16, possible chromosome combinations. How many chromosome combinations could result from fertilization between a fruit fly egg and a sperm cell?

6. 6 Meiosis and Genetic Variation Ch 5. 4 – Asexual Reproduction • Asexual reproduction is the creation of offspring from a single parent. These offspring are genetically identical to the parent. – Binary fission produces two daughter cells genetically identical to the parent cell. - Binary fission occurs in prokaryotes and is similar to mitosis that occurs in eukaryotes. In order for prokaryotes to increase their genetic diversity, they must undergo a process called conjugation. Fig 4. 1 –this image shows 3 individual bacteria, each at a different stage of binary fission. parent cell DNA duplicates cell begins to divide daughter cells

6. 6 Meiosis and Genetic Variation Ch 5. 4 Asexual Reproduction. • Budding forms a new organism from a small projection growing on the surface of the parent. This is a type of asexual reproduction in simple eukaryotic organisms. Synthesis: How might the asexual reproduction of genetically identical plants be useful to humans? How could it prove harmful to our food supply? Hydra bud Yeast Fig 4. 3 –budding occurs in simple fungi, plants and animals.

6. 6 Meiosis and Genetic Variation Ch 5. 4 Asexual Reproduction • Fragmentation is the splitting of the parent into pieces that each grow into a new organism. Examples: Flat worms and sea stars. • Vegetative reproduction forms a new plant from the modification of a stem or underground structure on the parent plant. Examples: strawberries and potatoes https: //www. elevise. co. uk/uploads/9/8/0/2/980215 60/screen-shot-2018 -03 -24 -at-11 -27 -40_orig. png

6. 6 Meiosis and Genetic Variation Ch 5. 4 –Advantages and Disadvantages of Asexual Reproduction • Environment determines what form of reproduction is most advantageous. – 1. Asexual reproduction is an advantage in consistently favorable conditions. If conditions change, it could become a disadvantage to reproduce asexually. – 2. Asexual reproduction does not involve attracting a mate. – 3. Asexual reproduction is a disadvantage when it comes to genetic variation. – 4. Asexual reproduction allows for rapid growth under ideal conditions. Fig 4. 2 –one bacterium can result in a total of 1024 cells after only 10 rounds of binary fission.