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Lecture 2

AN SC 431W Lecture 2: Lecture 2, 3

4 Pages

Animal Science
Course Code
AN SC 431W
Ott Troy

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ASEXUAL vs. SEXUAL REPRODUCTION A. Sexual Reproduction 1. Also known as “amphimixis” 2. Advantages a. Restore altered DNA to ensure high quality offspring b. Take advantage of changes over time, variable population b.i. Recombine and repair genes to adapt to environment b.ii. Select for good genes, then increase frequency in population c. Accumulate favorable traits in one offspring and eliminate mutation load c.i. Example: Syncytin accidentally produced by viral gene, now used to form placenta in mammals 3. Disadvantages a. Not fast or efficient, uses resources b. 2 fold cost of males b.i. ½ population (males) cannot reproduce b.ii. Only ½ of total male DNA passed down to offspring b.iii. Maladaptive traits: show female quality of male genes, but may cause danger of predators or competing males b.iii.1. Example: Male peacock’s colorful tail c. Internal vs. External fertilization c.i. Internal: less babies, more resources involved c.ii. External: laying eggs, males compete to fertilize d. Sexually transmitted diseases 4. Types of Sexual Reproduction a. Oviparity: egg laying (birds, turtles) b. Viviparity: live birth (humans, horses, dogs) c. Ovoviparity: carries internal eggs, hatch internally and born live (sharks, snakes) 5. Anisogamy: asymmetrical parental investment a. Egg: large, few in number, energetically expensive b. Sperm: small, many in number, energetically cheap c. Dissimilar gametes fuse to create zygote B. Asexual Reproduction 1. Also known as “apomixis” 2. Advantages a. Faster, more efficient using less resources b. Requires only one party c. No mating competition or maladaptive traits 3. Disadvantages a. Cannot combine favorable traits into one offspring—must be in lineage b. Not adaptable to environment, low variability c. No DNA recombination, offspring identical to parent d. Muller’s Ratchet d.i. In asexual population, likely no individual is free of harmful mutations d.ii. Each offspring has 1 mutation, next has 2, then 3, etc. d.iii. Keep adding mutation “chain” population goes downhill e. Red Queen Hypothesis e.i. Having to keep up with ever-changing environment e.ii. “Running at full speed to stay in same place” C. Reproduction in Humans 1. “Sex” vs. “Gender” a. Sex=male/female OR act of copulation b. Gender=male/female c. Cannot always be used interchangeably 2. Human male produces 10,000 sperm per heartbeat 3. Human female produces 1 ovum egg per estrous cycle 4. Human genome a. 25,000 genes in human genome (23 chromosome pairs) b.
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