Chapter 13 RQ 1. What are hereditary units of information called? 2. All chromosomes besides the X and Ys are known as _____________. 3. What keeps sister.

Chapter 13 RQ

1. What are hereditary units of information called?

2. All chromosomes besides the X and Ys are known as _____________.

3. What keeps sister chromatids together until anaphase?

4. What is the purpose of meiosis?5. 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 offspringBecause 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 offspringSperm and ova carrying each parents’ genes are combined in the nucleus of the fertilized egg

3. Distinguish between asexual and sexual reproduction.

AsexualSingle parent passes on all of its genesOffspring are genetically identical to parentResults in a cloneGenetic differences may occur as a result of mutation (change in DNA)

Sexual2 parents each parent passes on ½ of its genesOffspring have a unique combination of genes inherited from both parentsResults in greater genetic variation – offspring vary genetically from their siblings & parents

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); growthMeiosis gametes, haploid (23 chromosomes); sperm cells and ova

5. Distinguish among the life cycle patterns of animals, fungi, and plants.

AnimalsGametes are the only haploid (n) cellsMeiosis halves the cells (2n n + n)Fertilization makes the 2n organism

FungiOnly diploid (2n) stage is the zygoteResulting haploid (n) cells divide by mitosis to make the “n” organismGametes produced by mitosis

Life cycles…Plants

Alternate generations2n 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 I2. Metaphase I3. Anaphase I4. 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 occursMetaphase I tetrads align at metaphase plateAnaphase I homologues separate and are moved toward the poles by the spindle apparatusTelophase 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 II2. Metaphase II3. Anaphase II4. Telophase II and Cytokinesis

Meiosis II…

Prophase II spindle apparatus forms and chromosomes move toward the metaphase II plateMetaphase II chromosomes align singly on the metaphase plateAnaphase II centromeres of sister chromatids separate, sister chromatids of each pair move towards opposite poles of the cellTelophase 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 pairsCrossing 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.

Meiosis1. Is a reduction division2. Creates genetic variation3. Is 2 successive nuclear divisions- produces gametes in animalsMitosis- 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 ICrossing over – exchange of genetic material between homologues (prophase I)- occurs when homologous portions of 2 nonsister chromatids trade placesRandom 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)

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.

1. Sexual reproduction independent assortment, crossing over, random gamete fusion

2. Mutation random and rare structural changes made during DNA replication in a gene that could result from mistakes