1. GENETICS AND MEIOSIS UNIT 4 REVIEW Tiffany Crouch Remal Patel Jessenya Borrego 5/6/16 Period.2 Pre IB Biology Honors

2. What is Meiosis? ◦ Meiosis is a form of nuclear division that creates four haploid cells from one diploid cell. This process involves two rounds of cell division (Meiosis I and Meiosis II). Each round of cell division has four phases, which are similar to those in mitosis.

3. Reduction Division Meiosis occurs in germ cells to produce gametes. This process is sometimes called a “reduction division” because it reduces chromosomes number by half. In cells undergoing meiosis, DNA is copied once and but divided twice. Meiosis makes genetically unique haploid cells from a diploid cell. These haploid cells undergo more processing in the ovaries or testes, finally forming mature gametes.

4. Meiosis Results in Genetic Variation Crossing over, occurs during meiosis and helps create even greater variation. Crossing over is exchange of chromosome segments between homologous chromosomes during chromosomes during prophase I of meiosis I.

5. Continued … The farther apart two genes are located, the more likely they are to be separated when crossing over happens. Thus, genes located close together tend to be inherited together, which is called genetic linkage. Linked genes will be inherited in the same predicted ratios as would a single gene.

6. Mendel’s Laws Law of Segregation: ◦ Organisms inherit two copies of each gene, one from each parent. ◦ Organisms donate only one copy of each gene in their gametes. Thus, the two copies of each gene segregate, or separate, during gamete formation.

7. Mendel’s Laws Law of Independent Assortment: ◦ States that allele pairs separate independently of each other during gamete formation, or meiosis

8. Vocabulary Codominance: ◦ Which is when both traits are fully and separately expressed. Incomplete Dominance: ◦ Which a heterozygous phenotype is somewhere between the two homozygous phenotypes.

9. Continued… Polygenic Inheritance: ◦ Traits that are produced by two or more genes. Sex-Linked Genes: ◦ Genes that are located on the sex chromosomes.

10. Continued… Multiple Alleles: ◦ Is any of the alternative forms of a gene that may occur at a specific locus.

11. Importance of Mitosis Mitosis: ◦ Is the division of the cell nucleus and its contents. ◦ Mitosis is important for the growth of an organism and the repair of worn out parts of the body and in asexual reproduction.

12. What is Meiosis Meiosis: ◦ Is a form of a nuclear division that creates four haploid cell from one diploid cells

13. Stages of Mitosis Prophase ◦ The first and longest stage of mitosis. In this stage the chromosomes become visible and the centrioles separate and move to opposite poles of the cell.

14. Continued… Metaphase ◦ The second stage of mitosis. In this stage the chromosomes line up across the center of the cell and become connected to the spindle fiber at their centromere.

15. Continued… Anaphase ◦ The third stage of mitosis. In this stage the sister chromatids separate into individual chromosomes and are pulled apart.

16. Continued… Telophase ◦ The fourth and last stage of mitosis. During this stage the chromosomes gather at opposite ends of the cell and lose their distinct rod-like shapes. Two new nuclear membranes then form around each of the two regions of DNA and the spindle fibers disappear.

17. Stages of Mitosis Prophase I ◦ The nuclear membrane breaks done. The centrosomes and centrioles begin to move, and spindle fibers start to assemble. The duplicated chromosomes condense, and homologous chromosomes begin to pair up.

18. Continued… Metaphase I ◦ Spindle fibers align the homologous chromosomes along the cell equator. Each side of the equator has chromosomes from both parents.

19. Continued… Anaphase I ◦ The paired homologous chromosomes separate from each other and move toward opposite sides of the cell. Sister chromatid remain attached.

20. Continued… Telophase I ◦ The spindle fibers disassemble and the cell undergoes cytokinesis.

21. Continued Prophase II ◦ The centrosomes and centrioles move to opposite sides of the cell, and spindle fibers start to assemble.

22. Continued… Metaphase II ◦ Spindle fibers align the chromosomes along the cell equator.

23. Continued… Anaphase II ◦ The sister chromatids are pulled apart from each other and move to opposite sides of the cell

24. Continued… Telophase II ◦ The nuclear membranes form again around the chromosomes, the spindle fibers break apart, and the cell undergoes cytokinesis.

25. Review What are the advantages and disadvantages of sexual and asexual reproduction?

26. Review How does meiosis ensure genetic diversity?

27. Review When does independent assortment and crossing over occur during the process of meiosis?

28. Review How are mitosis and meiosis similar and different?

29. Review What do Mendel’s Laws tell us about the patterns of inheritance?

30. Review What are the results for the different patterns of inheritance?

31. Review In a certain species of plant, the color purple (P) is dominant to the color white (p). According to the Punnett Square, what is the probability of an offspring being purple? A)25% B)0% C)100% D)75%

32. Review In a certain species of plant, the color purple (P) is dominant to the color white (p). According to the Punnett Square, what is the probability of an offspring being purple? A)75% B)25% C)50% D)100%