Presentation on theme: "Meiosis: Georgia Performance Standards: Using Mendel’s laws, explain the role of meiosis in reproductive variability. Essential Questions: How does meiosis."— Presentation transcript:
Meiosis: Georgia Performance Standards: Using Mendel’s laws, explain the role of meiosis in reproductive variability. Essential Questions: How does meiosis generate variation in offspring?
Forever Linked? Some genes appear to be inherited together, or “linked.” If two genes are found on the same chromosome, does it mean they are linked forever? Study the diagram, which shows four genes labeled A–E and a–e, and then answer the questions on the next slide. Section 11-5 Go to Section:
Linked Genes Warm-up 1. In how many places can crossing over result in genes A and b being on the same chromosome? 2. In how many places can crossing over result in genes A and c being on the same chromosome? Genes A and e? 3. How does the distance between two genes on a chromosome affect the chances that crossing over will recombine those genes?
Linked Genes: It’s easy to see how genes located on different chromosomes assort independently, but what about genes located on the same chromosome? Wouldn’t they generally be inherited together?
Linked Genes First, each chromosome is actually a group of linked genes. Second, Mendel’s principle of independent assortment still holds true. It is the chromosomes, however, that assort independently, not individual genes.
Genes and Linkage: If two genes are found on the same chromosome, does this mean that they are linked forever? Not at all. Crossing-over separates genes that had been on the same chromosome onto homologous chromosomes. Crossover events –separate and exchange linked genes –produce new combinations of alleles –it helps to generate genetic diversity.
Gene Maps A gene map shows the relative locations of each known gene on a chromosomes Recombination rates –measure the frequencies of crossing-over between genes –used to construct genetic maps Ex: human genome map
Earth Country State City People Cell Chromosome Chromosome fragment Gene Nucleotide base pairs Section 11-5 Comparative Scale of a Gene Map Go to Section: Mapping of Earth’s Features Mapping of Cells, Chromosomes, and Genes
Exact location on chromosomesChromosome 2 Section 11-5 Figure Gene of the Fruit Fly Go to Section:
Checkpoint Questions: 1. How does the principle of independent assortment apply to chromosomes? 2. What are gene maps, and how are they produced? 3. How does crossing-over make gene mapping possible? 4. If two genes are on the same chromosome but usually assort independently, what does that tell you about how close together they are?