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Key Questions:
1. What are the steps of the cell cycle? (this will be answered by everyone as part of an assignment)
2. How is the genetic material handled during mitosis so that identical offspring are produced? DONE
The strands of chromatin are copied during the S phase of interphase so there are two identical copies of each chromosome. They remain connected in the middle for organizational purposes. During prophase they coil up into duplicated chromosomes made up of two identical sister chromatids. These duplicated chromosomes are lined up in the middle of the cell and the sister chromatids split apart into daughter chromosomes and travel to opposite ends of the cell so each cell has an identical copy of chromosomes when the cell splits during cytokinesis. From this, two identical cells are created with 46 chromosomes each.
3. How is the same genetic material handled during meiosis so that variable offspring are produced? (this would include a thorough discussion of independent assortment and crossing-over) PLEASE ILLUSTRATE / EXPLAIN INDEPENDENT ASSORTMENT AND CROSSING-OVER MORE THOROUGHLY BY INCLUDING AN EXAMPLE. TO HELP YOU GET STARTED HOW ABOUT EXPLAINING HOW AN INDIVIDUAL WITH THE GENOTYPE AaBb COULD PRODUCE AB, Ab, aB, and ab gametes through indpendent assortment if the two genes were on separate chromosomes, and then explain how the organism could also produce these same four gametes if the two genes were on the same chromosome.
During meiosis genetic variability is produced partially due to chance and partially due to a process called crossing over. In the first step of meiosis, Prophase I, crossing over takes place, where the homologous pairs embrace during synapsis and exchange genetic material. This does not cause the duplicated chromosomes to be missing any genes but just exchanges alleles between it and its homologous pair that also codes for the same genes (that will eventually become genotype traits, and possibly phenotype traits). The other factor that allows for variable offspring is simply chance, or independent assortment. During Metaphase I in meiosis the duplicated chromosomes and its homologous partner lineup along the diploid cell's equator in no specific left/right order. The different possible genetic variations per offspring cell are 2n, so if a cell has 23 homologous pairs there are 8,388,608 different options for the offspring haploid cell.
4. What are the advantages and disadvantages of asexual and sexual reproduction? DONE
Asexual reproduction seems to be the better of both sexual and asexual reproduction, but there are numerous disadvantages to this way of reproduction. First, the advantages are the high speed and the small amount of energy needed to create a direct copy of the parent. Second, asexual reproduction seems to be the smarter choice. Why try to recreate another being when you have one that is perfectly healthy? It would be smart to copy something that works well. But, with these advantages come disadvantages. If we were to of made direct copies of our self, our ancestors could of gone extinct with environmental changes. Our ancestors would have eventually died about because of the constant changes. It is not about to future, but rather the past and how we adapted to change. Sexual reproduction also has its advantages and disadvantages. Sexual reproduction involves more energy, puts new beings at risk of having different mutations, and could take a healthy being and create a sick off spring. There are many more variables involved with sexual reproduction. Advantages would be the fact that we have such a diverse community. Direct copies of our ancestors duplicated over and over would give us no diversity, and sexual reproduction allows you to have more than 2^46 possibilities.
5. What types of mutations involve whole chromosomes and chromosome segments?
Explain the difference between:
6. asexual and sexual reproduction DONE
Asexual reproduction is a form of reproduction by which cells or individuals inherit ALL genetic material from ONE parent and happens for one of three reasons: Growth, repair, or reproduction of an organism. Asexual reproduction occurs constantly throughout your body for these reasons. Sexual reproduction, however, is the division of a cell in eukaryotic organisms by meiosis and produces sex cells that have half the chromosome number (haploid) compared to the cell they descended from.
7. chromatin and chromosomes DONE
During prophase the long, thin fibers of chromatin coil up forming distinct chromosomes.
8.cytokinesis and telophase DONE
Telophase is the process is in which the diploid or haploid nucleus begins to elongate and prepares to be split during mitosis or meiosis. The daughter chromosomes move to the poles of the cell while a nuclear envelope builds around the chromosomes at each of the cell. Cytokinesis is different from Telophase in that it is the actual division of the diploid or haploid cell into two new daughter cells. A cleavage furrow is created and this is where the division will occur.
9. animal cytokinesis and plant cytokinesis DONE
Cytokinesis is the split of cytoplasm during mitosis or meiosis. In animal cytokinesis, a cleavage furrow is formed between the forming daughter cells, whereas in a plant, a cell plate forms, dividing the original cell's wall into two new cell walls to enclose each of the two new daughter cells.
10. somatic cells and gametes DONE
Somatic cells, which are cells that make up the body, always have the diploid number of chromosomes as a result of them dividing through mitosis. Gametes, also known as sex cells (sperm and eggs), always have a haploid number due to their formation through meiosis.
11. haploid and diploid DONE
In eukaryotic organisms, the haploid number, or 1n, refers to one set of genes that is given to the gametes (either eggs or sperm) through the process of meiosis. For example, the haploid number for humans is 23.
The diploid number, or 2n, refers to the two sets of genes (23 from your mom and 23 from your dad) to create two sets with a total of 46 for humans. All somatic cells, or body cells, have the diploid number of chromosomes.
12. sister chromatids and homologous chromosomes DONE
When chromatin begins to coil into chromosomes in prophase of mitosis, the duplicated chromosomes are composed of two genetically identical sister chromatids, so that when the 46 duplicated chromosomes of a human cell separate during anaphase into 2 groups of daughter chromosomes, 2 identical groups of genetic material result and can then produce two identical cells. However, when a cell is preparing to create haploid gametes for sexual reproduction, the goal is not 2 identical, 46-chromosome sets, but half that- 23 chromosomes. The chromosomes in prophase I of meiosis are constructed the same way, each chromosome consisting of 2 sister chromatids, but each chromosome is arranged with its allele, the alternate version of say, the gene for ear lobes, which the cell received from its mother and father. Each human cell contains 2 sets of genes, one from a mother and one from a father. Homologous pairing is just the matching of corresponding genes from the mother and father, which can vary in trait ("A" v. "a"). So, to wrap this all up, sister chromatids are genetically identical pairs of coiled chromatin which make up chromosomes. Homologous chromosomes are a pair of chromosomes, each consisting of sister chromatids, but can differ from its allele chromosome in terms of genetic material.
13. prophase I and prophase DONE
Both Prophase I and prophase occur in a diploid cell, not a gamete. However, during meiosis when Prophase I occurs synapsis and crossing over take place. During synapsis the homologous pairs of duplicated chromosomes attach to each other and cross over, exchanging alleles between the chromatids of the two members of the pair, allowing for genetic variation in the eventual cells that are produced.
14. crossing-over and independent assortment NOT METAPHASE (LINE 2) (METAPHASE IS PART OF MITOSIS, NOT MEIOSIS), IT'S NOT "THE RANDOM DECISOIN OF WHICH CHROMATID….IS ON THE RIGHT SIDE VS ON THE LEFT SIDE - USE A DIFFERENT VOCABULARY TERM IN PLACE OF CHROMATID, NOT PROPHASE (LINE 4)
Both processes offer methods of providing genetic variability within gametes, but in their own ways. Independent assortment occurs as the cell undergoes metaphase, and is the random decision of which chromatid of a pair of sister chromatids is on the right side vs on the left. Crossing over takes place in prophase, and is the switching of alleles within the same gene of a pair of homologous chromosomes. With both of these methods of providing genetic variability, it is almost impossible to produce two identical gametes.
15. nondisjunction and Down syndrome
Show a relationship between the following sets of terms:
16. meiosis / haploid / fertilization DONE
Meiosis is a process of cell division that produces haploid gametes. During fertilization, one gamete from the father, a haploid sperm cell, reaches and fuses with another gamete from the mother, a haploid egg cell.
17. homologous chromosomes / gene / allele DONE, BUT I'D RATHER SEE YOU DESCRIBE HOMOLOGOUS CHROMOSOMES AS A PAIR OF DUPLICATED CHROMOSOMES, ONE INHERITED FROM THE MOTHER AND ONE FROM THE FATHER, WITH THE SAME GENES, BUT DIFFERENT ALLELES
During crossing over, alleles of the same gene within a pair of homologous chromosomes switch places in order to increase the variety of genetic possibilities.
18. diploid / somatic cells / mitosis DONE
Mitosis is a process in which the nucleus divides in somatic, or body, cells, each cell having a diploid number of chromosomes.
19. haploid / gametes / meiosis DONE
Gametes, the collective term for egg and sperm cells, are haploid cells, meaning that they have a single chromosome set with a haploid number (n) of 23 chromosomes. The chromosome number is cut in half to form these haploid cells through the process of cell division known as meiosis.
20. anaphase I / homologous pairs / spindle fibers DONE
In anaphase I, the two rows of homologous pairs move apart (each haploid set of duplicated chromosomes moves to opposite poles) because the spindle fibers, which are connected to the duplicated chromosomes via the kinetochore, shorten, meaning that they pull the duplicated chromosomes to opposite poles.
