Chapter 7 Meiosis

1. Chapter 7 Meiosis Meiosis Forms Haploid Cells

2. The Basics of Meiosis Animals and plants practice s______ reproduction, with parents passing chromosomes to their offspring. Because each child receives unique combinations of chromosomes from the p______, each child differs from the parents.

3. The Basics of Meiosis (cont.) The chromosomes of each parent exist in pairs called homologues, or h_________ chromosomes. The pairs are identical in size, shape, construction, and the g_____ they contain. However the homologues within an organism may contain different versions, or alleles, of those genes.

4. The Basics of Meiosis (cont.)

5. The Basics of Meiosis (cont.) In humans, there are __ pairs of homologous chromosomes. There are __ pairs of autosomes. The sex chromosomes comprise the last pair. Males have an _ and a smaller _ chromosome. Females have two equal _ chromosomes.

6. The Basics of Meiosis (cont.) With 23 pairs of chromosomes, humans have a total of __ chromosomes. This total number of chromosomes is called the d______ number.

7. The Human Life Cycle The human life cycle involves two types of cell division. � M______ � M______

8. The Human Life Cycle (cont.) Mitosis is involved in the g______ of a child and repair of tissues. Meiosis is a special form of cell division associated with s______ reproduction. Meiosis produces special reproductive cells called g_______ (eggs and sperm in humans). Gametes have only ___ chromosome of each chromosome pair (e.g., 23 instead of 46).

9. The Human Life Cycle (cont.) In males, meiosis is part of s______ production (spermatogenesis). In females, meiosis is part of e___ production (oogenesis). During fertilization, an egg and sperm unite to form a z_____, restoring the chromosomes to 46 total.

10. The Human Life Cycle (cont.)

11. Overview of Meiosis Meiosis involves t__ cellular divisions. � Meiosis I � Meiosis II These two cellular divisions produce f____ daughter cells, each with one chromosome of each pair.

12. Overview of Meiosis (cont.) During meiosis I, the h_________ chromosomes pair up to form sister chromatids of two homologous chromosomes. Later in meiosis I, the homologous pairs s_______ to provide one member of each homologous pair to each daughter cell. After meiosis I, the daughter cells have half the number of c____________, but each chromosome consists of two sister chromatids.

13. Overview of Meiosis (cont.) During meiosis II, the sister chromatids are s__________. The two divisions of meiosis insure that the g________ produced by an individual have unique combinations of homologous chromosomes.

14. Overview of Meiosis (cont.)

15. Crossing-Over While a homologous chromosomes pair up during meiosis I, the homologues may exchange g_______ material by crossing-over. Crossing-over recombines the alleles of the h___________ chromosomes, creating new combinations and increasing the genetic variability of the gametes.

16. Crossing-Over (cont.)

17. The Importance of Meiosis One reason meiosis is important is that it maintains the same number of chromosomes in each new g__________. Another reason meiosis is important is that it contributes new c__________ of alleles to each new generation.

18. The Importance of Meiosis Meiosis produces gametes with many different combinations of h__________ chromosomes.

19. The Phases of Meiosis The same four stages of mitosis occur during meiosis. � P________ � Metaphase � Anaphase � Telophase The four stages occur t____, once during meiosis I and again during meiosis II.

20. The First Division � Meiosis I Significant events occur during prophase I of meiosis. The spindle appears between the separating centromeres. The h_________ chromosomes pair up as they condense. C______-over between homologous chromosomes may occur. At metaphase I, the pairs of homologous chromosomes are attached to the spindle and are aligned at the spindle e________.

21. The First Division � Meiosis I (cont.) The homologous chromosomes are separated during a________ I. Anaphase I is the point at which the diploid cell becomes h_______. During telophase I, the nuclear m________ reforms around the now haploid nuclei.

22. The First Division � Meiosis I (cont.)

23. The Second Division � Meiosis II The events that occur during m______ II are essentially the same as those that occur during mitosis. As prophase II begins, a s_______ appears and the nuclear membrane and nucleolus disappear. During metaphase II the chromosomes made up of two chromatids line up at the spindle e_____.

24. The Second Division � Meiosis II (cont.) The sister chromatids of the chromosomes s_______ during anaphase II and begin migrating towards the poles. The spindle d_________ and the nuclear envelope reforms in telophase II. Cytokinesis occurs to complete the meiosis. In summary, a single diploid cell undergoes meiosis to produce ____ haploid gametes.

25. The Second Division � Meiosis II (cont.)

26. Meiosis Compared to Mitosis Meiosis requires ___ nuclear divisions while mitosis requires only one. Meiosis produces ____ daughter nuclei while mitosis produces only two. Both meiosis and mitosis are typically followed by c_________.

27. Meiosis Compared to Mitosis (cont.) After meiosis, the daughter nuclei are haploid and contain h___ the chromosome number of the parent cell. Following mitosis, the daughter cells have the s____ chromosome number as the parent cell.

28. Meiosis Compared to Mitosis (cont.) The daughter cells of meiosis are g_________ dissimilar from the parent cell. The daughter cells of mitosis are genetically i_______ to the parent cell.

29. Meiosis Compared to Mitosis (cont.)

30. Occurrence Meiosis occurs only at specific times during the life cycle of sexually reproducing organisms. Meiosis in humans occurs only in the t_____ and o______. Mitosis is common and occurs throughout the b____.

31. Process There are several events that distinguish meiosis I from mitosis. Homologous chromosomes pair up during m_______ and crossing-over can occur during prophase I. This does not occur during mitosis.

32. Process The homologous p____ of chromosomes align at the spindle equator during metaphase I of meiosis. In mitosis, the chromosomes align during metaphase. During anaphase I, the homologous chromosomes s________ while in anaphase of mitosis, the sister chromatids separate.

33. Process (cont.)

34. Process (cont.) The events of meiosis II are the same as mitosis.

35. Process (cont.)