The Study of Heredity and Variation in Organisms

1. __________is the study of heredity (transmission of traits from one generation) and variation. CHAPTER 13 MEIOSIS AND SEXUAL LIFE CYCLES • 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 ___________ Know these terms! • 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 Fig. 13.3

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

6. _______ - The fertilized egg with two haploid sets of chromosomes- one from mom, one from dad ________ - 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) Gametes develop by _________ instead of mitosis in which the chromosome number is halved. Fig. 13.5

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 How??- By copying chromosomes once, but dividing twice. Meiosis I – separates ____________________ Meiosis II-separates ______________________ Fig. 13.7

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

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 Meiosis Mitosis ___ End result ____ ________ ________ Daughter cells _____ ____ Chiasmata? __ __ # of divisions Purpose ________ _________ ____________are the physical manifestation of crossing over, a form of genetic rearrangement.

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 1. _____________________ • A fifty-fifty chance that a particular daughter cell of _______ will get the maternal chromosome of a certain homologous pair • For humans with n = 23, there are about 8 ________ possible combinations of chromosomes. Gametes Fig. 13.9

13. Four mechanisms.. (Cont.) 2. ___________________- • -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. Fig. 13.11

14. 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 223 (8 million) ________________________ A zygote is composed of 1 in 70 trillion (223 x 223) possible combinations of chromosomes. __________________ adds even more variation to this. • Four mechanisms.. (Cont.) 3. _____________________

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