Chapter 13 RQ What are hereditary units of information called? All chromosomes besides the X and Ys are known as _____________. What keeps sister chromatids together until anaphase? What is the purpose of meiosis? What is the term for a fertilized egg?

1. Explain why organisms only reproduce their own kind, and why offspring more closely resemble their parents than unrelated individuals of the same species. It is a consequence of heredity, which results from the transmission of genes from parents to offspring Because they share similar genes, offspring more closely resemble their parents or close relatives than others 

2. Explain what makes heredity possible. DNA is precisely replicated producing copies of genes that can be passed along from parents to offspring Sperm and ova carrying each parents’ genes are combined in the nucleus of the fertilized egg 

3. Distinguish between asexual and sexual reproduction. Single parent  passes on all of its genes Offspring are genetically identical to parent Results in a clone Genetic differences may occur as a result of mutation (change in DNA) Sexual 2 parents  each parent passes on ½ of its genes Offspring have a unique combination of genes inherited from both parents Results in greater genetic variation – offspring vary genetically from their siblings & parents 

Mitosis  somatic cells, diploid (46 chromosomes); growth 4. Diagram the human life cycle and indicate where in the human body that mitosis and meiosis occur; which cells are the result of meiosis and mitosis; and which cells are haploid. Mitosis  somatic cells, diploid (46 chromosomes); growth Meiosis  gametes, haploid (23 chromosomes); sperm cells and ova 

5. Distinguish among the life cycle patterns of animals, fungi, and plants. Gametes are the only haploid (n) cells Meiosis halves the cells (2n  n + n) Fertilization makes the 2n organism 

Fungi Only diploid (2n) stage is the zygote Resulting haploid (n) cells divide by mitosis to make the “n” organism Gametes produced by mitosis 

Life cycles… Plants Alternate generations 2n stage – sporophyte (makes spores by meiosis) Haploid spores divide mitotically to produce a multicellular haploid gametophyte (haploid gametes produced by mitosis) Fertilization produces a diploid zygote – sporophyte 

6. List the phases of meiosis I and meiosis II and describe the events characteristic of each phase. Meiosis I  cell division that segregates the two chromosomes of each homologous pair and reduces the chromosome number by one-half; includes four phases: 1. Prophase I 2. Metaphase I 3. Anaphase I 4. Telophase I and Cytokinesis 

Meiosis I… Prophase I  long and complex; 90% of time for meiosis - synapsis occurs (homologous chromosomes come together to form a tetrad; four chromatids) - crossing over occurs Metaphase I  tetrads align at metaphase plate Anaphase I  homologues separate and are moved toward the poles by the spindle apparatus Telophase I & cytokinesis  the spindle apparatus continues to separate homologous chromosome pairs until the chromosomes reach the poles 

Meiosis II… Meiosis II  this division separates sister chromatids of each chromosome; includes four phases: 1. Prophase II 2. Metaphase II 3. Anaphase II 4. Telophase II and Cytokinesis 

Meiosis II… Prophase II  spindle apparatus forms and chromosomes move toward the metaphase II plate Metaphase II  chromosomes align singly on the metaphase plate Anaphase II  centromeres of sister chromatids separate, sister chromatids of each pair move towards opposite poles of the cell Telophase II and cytokinesis  nuclei form at opposite poles of the cell - cytokinesis occurs producing four haploid daughter cells 

7. Describe the process of synapsis during prophase I, and explain how genetic recombination occurs. Synapsis  homologous chromosomes come together as pairs Crossing over can happen where the nonsister chromatids are linked 

8. Describe key differences between mitosis and meiosis; explain how the end result of meiosis differs from that of mitosis. Meiosis 1. Is a reduction division 2. Creates genetic variation 3. Is 2 successive nuclear divisions - produces gametes in animals Mitosis - crossing over doesn’t occur - occurs in somatic cells (body cells) - copies the cells 

9. Explain how independent assortment, crossing over, and random fertilization contribute to genetic variation in sexually reproducing organisms. Independent assortment – orientation of the chromosome pairs is random at the poles (meiosis I) - each homologous pair orients independently of the others at metaphase I Crossing over – exchange of genetic material between homologues (prophase I) - occurs when homologous portions of 2 nonsister chromatids trade places Random fertilization – an egg is representative of 1 in 8 million possible chromosome combinations (same with sperm) - resulting zygote can have 1 in 64 trillion possible diploid combinations (not including crossovers) 

It is the basis for natural selection 10. Explain why inheritable variation was crucial to Darwin’s theory of evolution. It is the basis for natural selection - variations selected that increase reproductive success - adaptation (the accumulation of heritable variations) 

11. List the sources of genetic variation. Sexual reproduction  independent assortment, crossing over, random gamete fusion Mutation  random and rare structural changes made during DNA replication in a gene that could result from mistakes 