Genetic Diversity: Independent Assortment and Crossing Over in Meiosis

1. KEY CONCEPT Independent assortment and crossing over during meiosis result in genetic diversity.

2. Sexual reproduction creates unique combinations of genes. • Sexual reproduction creates unique combination of genes. • independent assortment of chromosomes in meiosis • random fertilization of gametes • Unique phenotypes may give a reproductive advantage to some organisms.

3. Crossing over during meiosis increases genetic diversity. • Crossing over is the exchange of chromosome segments between homologous chromosomes. • occurs during prophase I of meiosis I • results in new combinations of genes

4. Chromosomes contain many genes. • The farther apart two genes are located on a chromosome, the more likely they are to be separated by crossing over. • Genes located close together on a chromosome tend to be inherited together, which is called genetic linkage. • Genetic linkage allows the distance between two genes to be calculated.

5. KEY CONCEPT DNA replication copies the genetic information of a cell.

6. Replication copies the genetic information. • A single strand of DNA serves as a template for a new strand. • The rules of base pairing directreplication. • DNA is replicated during theS (synthesis) stage of thecell cycle. • Each body cell gets acomplete set ofidentical DNA.

7. nucleotide The DNA molecule unzips in both directions. Proteins carry out the process of replication. • DNA serves only as a template. • Enzymes and other proteins do the actual work of replication. • Enzymes unzip the double helix. • Free-floating nucleotides form hydrogen bonds with the template strand.

8. nucleotide new strand DNA polymerase • DNA polymerase enzymes bond the nucleotides together to form the double helix. • Polymerase enzymes form covalent bonds between nucleotides in the new strand.

9. new strand original strand Two molecules of DNA • Two new molecules of DNA are formed, each with an original strand and a newly formed strand. • DNA replication is semiconservative.

10. There are many origins of replication in eukaryotic chromosomes. Replication is fast and accurate. • DNA replication starts at many points in eukaryotic chromosomes. • DNA polymerases can find and correct errors.

11. KEY CONCEPT Mutations are changes in DNA that may or may not affect phenotype.

12. mutated base Some mutations affect a single gene, while others affect an entire chromosome. • A mutation is a change in an organism’s DNA. • Many kinds of mutations can occur, especially during replication. • A point mutation substitutes one nucleotide for another.

13. Many kinds of mutations can occur, especially during replication. • A frameshift mutation inserts or deletes a nucleotide in the DNA sequence.

14. Chromosomal mutations affect many genes. • Chromosomal mutations may occur during crossing over • Chromosomal mutations affect many genes. • Gene duplication results from unequal crossing over.

15. Translocation results from the exchange of DNA segments between nonhomologous chromosomes.

16. blockage no blockage Mutations may or may not affect phenotype. • Chromosomal mutations tend to have a big effect. • Some gene mutations change phenotype. • A mutation may cause a premature stop codon. • A mutation may change protein shape or the active site. • A mutation may change gene regulation.

17. Some gene mutations do not affect phenotype. • A mutation may be silent. • A mutation may occur in a noncoding region. • A mutation may not affect protein folding or the active site.

18. Mutations in body cells do not affect offspring. • Mutations in sex cells can be harmful or beneficial to offspring. • Natural selection often removes mutant alleles from a population when they are less adaptive.

19. Mutations can be caused by several factors. • Replication errors can cause mutations. • Mutagens, such as UV ray and chemicals, can cause mutations. • Some cancer drugs use mutagenic properties to kill cancer cells.

20. KEY CONCEPT A population shares a common gene pool.

21. Genetic variation in a population increases the chance that some individuals will survive. • Genetic variation leads to phenotypic variation. • Phenotypic variation is necessary for natural selection. • Genetic variation is stored in a population’s gene pool. • made up of all alleles in a population • allele combinations form when organisms have offspring

22. measures how common allele is in population • can be calculated for each allele in gene pool • Allele frequencies measure genetic variation.

23. Genetic variation comes from several sources. • Mutation is a random change in the DNA of a gene. • can form new allele • can be passed on to offspring if in reproductive cells • Recombination forms new combinations of alleles. • usually occurs during meiosis • parents’ alleles arranged in new ways in gametes

24. Genetic variation comes from several sources. • Hybridization is the crossing of two different species. • occurs when individuals can’t find mate of own species • topic of current scientific research