1. CHAPTER 13 MEIOSIS AND SEXUAL LIFE CYCLES __________ is the study of heredity (transmission of traits from one generation) and variation. Genes are segments of _____. program cells to synthesize specific enzymes and other proteins that produce an organism’s inherited traits Consist of four __________________ program specific traits that emerge as we develop from fertilized eggs into adults.

2. The transmission of hereditary traits has its molecular basis in the precise __________ of DNA Most DNA in a eukaryotic cell is subdivided into _________________ in the nucleus. Some DNA exists in ___________ and ____________. Every living species has a characteristic number of chromosomes. Humans have 46 in almost all of their cells. Chromosomes consist of a single ____ molecule in association with various ________. Each chromosome has hundreds or thousands of genes, each at a specific location, it’s _____.

3. ________________- occurs mostly in single-cell eukaryotes, by mitotic cell division to produce two identical daughter cells _________________- results in greater variation among offspring than does _________reproduction. Offspring of sexual reproduction vary _____________ from their siblings and from both parents. Figure not in text

4. Humans contain 46 chromosomes in each _____________ (all cells except germ cells) and 23 in the ________ (sperm or ovum). 1. Fertilization and ___________ We have ____________ ________________ pairs that carry genes that control the same inherited characters. An exception - the _____ ___________ (X and Y). Females are XX and males are XY Know these terms! Fig. 13.3

5. _____________ - an ordered displays of an individual’s chromosomes - used to detect large abnormalities Fig. 13.3

6. ________ - Germ cells with one set of chromosomes (22 __________ and an X or a Y in humans). ________ - Somatic cells with two sets of chromosomes (46 total in humans) _______ - The fertilized egg with two haploid sets of chromosomes- one from mom, one from dad Fig. 13.5 Gametes develop by _________ instead of mitosis in which the chromosome number is halved.

7. In meiosis, there are two consecutive cell divisions, __________ and ___________ which results in four haploid daughter cells. 2. Meiosis reduces chromosome number from diploid to haploid Fig. 13.7 How??- By copying chromosomes once, but dividing twice. Meiosis I – separates ____________________ Meiosis II-separates ______________________

8. 4 phases: prophase, metaphase, anaphase, and telophase. ___________ - Previously replicated chromosomes join together at many locations to exchange DNA Meiosis I These exchange points are called _________ Spindles form from ___________ Metaphase, anaphase and telophase are similar to those in __________ MetaphaseAnaphase End result- 2 ________ cells Fig. 13.8

9. Meiosis II is very similar to mitosis BUT- DNA is not ___________ first. Meiosis II Prophase, metaphase, anaphase or telophase occur End result- 4 _____ cells Fig. 13.8

10. Comparison of mitosis and meiosis End result ___ ____ Daughter cells ________ Chiasmata? MeiosisMitosis _________ ____________ are the physical manifestation of crossing over, a form of genetic rearrangement. # of divisions __ Purpose_________________

11. Mitosis produces two _________ daughter cells, but meiosis produces 4 very different cells. Fig. 13.8

12. Four mechanisms contribute to genetic variation: 3. Sexual life cycles produce genetic variation among offspring A fifty-fifty chance that a particular daughter cell of _______ will get the maternal chromosome of a certain homologous pair Gametes 1. _____________________ For humans with n = 23, there are about 8 ________ possible combinations of chromosomes. Fig. 13.9

13. 2. ___________________- Four mechanisms.. (Cont.) Fig. 13.11 -homologous portions of two nonsister chromatids trade placesin meiosis I. produces ____________ ____________ which combine genes inherited from each parent. For humans, this occurs ______ ________ per chromosome pair.

14. 3. _____________________ Any sperm can fuse with any egg. A zygote produced by mating of a woman and man has a unique genetic identity. A given ovum and sperm each have 2 23 (8 million) ________________________ A zygote is composed of 1 in 70 trillion (2 23 x 2 23 ) possible combinations of chromosomes. __________________ adds even more variation to this. Four mechanisms.. (Cont.)

15. This results in adaptation, the accumulation of favorable genetic variations. 4. _ __________________ New genetic _________________ that work best in the new conditions will produce more offspring and these genes will increase. Four mechanisms.. (Cont.)