Official Biology Project4-1.

8/9/2019 Official Biology Project4-1.

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Prophase I. The chromosomes condense, and the nuclear envelope breaks down. Homologous

chromosomes pair along their length. Crossing-over occur when portions of a chromatid on one

homologous chromosome are broken and exchanged with the corresponding chromatid portions of the

other homologous chromosome.


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Metaphase I. The pairs of homologous chromosomes are moved by the spindle to the equator of the

cell. The homologous chromosomes remain together.


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Anaphase I. the homologous chromosomes separate. As in mitosis, the chromosomes of each pair are

pulled to opposite poles of the cell by the spindle fibers. But the chromatids do not separate at their

centromeres each chromosome is still composed of two chromatids, the gentic material, however, has

recombined.


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Telophase I and cytokinesis. Individual chromosomes gather at each of the poles. In most organisms, the

cytoplasm divides, forming two new cells. Both cells or poles contain one chromosome from each pair of

homologous chromosomes.


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Prophase II. A new spindle forms around the chromosomes.


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Metaphase II. The chromosomes line up along the equator and are attached to their centromeres to

spindle fibers.


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Anaphase II. The centromeres divide, and the chromatids move to opposite poles of the cell.


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Telophase II and cytokinesis. A nuclear envelope forms around each set of chromosomes. The spindle

breaks down, and the cell undergoes cytokinesis. The result of meiosis if four haploid cells.


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Meiosis a process in cell division during which the number of chromosomes decreases to half the

original number by two divisions of the nucleus, which results in the production of sex cells.

Sexual reproduction reproduction in which gametes from two parents unite.

Crossing-over the exchange of genetic material between homologous chromosomes during

meiosis; can result in genetic recombination.

Genetic recombination is the process by which a strand of genetic material is broken and then joined

to a different DNA molecule.

Homologous chromosomes chromosomes that have the same sequence of genes, have the same

structure, and that pair during meiosis.

Gamete a haploid reproductive cell that unites with another haploid reproductive cell to form a

zygote.

2. In what organs in the human body do cells undergo meiosis?

The reproductive organs.

3. During interphase of the cell cycle, how does a cell prepare for dividing?

In the G2 phase, preparations are made for the nucleus to divide. Hollow protein fibers called

microtubules are rearranged during G2 in preparation for mitosis.

4. Based on the objective for this lab, write a question you would like to explore about meiosis.

I would like to know if you could take a deformed organisms cell and use meiosis to repair it.

Part A: design a model.

I used pencil for the outline of the cell and the nucleus. I used pipe cleaners for the chromosomes and

beads for the homologous chromosomes.

Part B: test hypothesis.


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5. In humans, gametes result from meiosis. Will all gametes produced by one parent be identical?In human beings, gametes produced by one parent will not be identical. Crossing-over and

independent assortment provides a great number of possibilities for each gamete produced.

6. When an egg and a sperm fuse during sexual reproduction, the resulting cell is called a zygote.How many copies of each chromosome and each gene will be found in a zygote?

In a zygote, 2 copies of each chromosome and gene will be found. One coming from the sperm

and one coming from the egg.

7. Crossing-over frequently occurs between the chromatids of homologous chromosomes duringmeiosis. Under what circumstances does crossing-over result in new combination of genes in

gametes?

The circumstance in which crossing-over results in new combinations of genes in gametes is

called independent assortment. Independent assortment is the random distribution of

homologous chromosomes during meiosis. In humans, for example, each of the 23 pairs of

chromosomes segregate independently. Thus, 223

gametes with different gene combinations can

be produced from one original cell by this mechanism.

8. Synapsis must occur before crossing-over can take place. How would the outcome of meiosis bedifferent if synapsis did not occur?

The outcome would be that the offspring would look exactly like one of the parents. Since

crossing-over didnt occur, there would only be chromosomes from one parent, not homologous

pairs of chromosomes (one chromosome coming from each parent to make a pair). The

offspring would be identical to one parent because it didnt have any genes from the other

parent.

1. Analyzing Results. How do the nuclei you made by modeling meiosis compare with the nucleusof the cell you started with? Explain your results.

In the beginning, the nucleus of the model cell had 46 chromosomes inside. In the end, after the

process o f meiosis, there were 2 haploid offspring cells that each contained 23 chromosomes.


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2. Recognizing Relationships. How are homologous chromosomes different from chromatids?Homologous chromosomes are similar to each other in size, shape and genetic content. But

each part of the pair comes from a different gamete. Homologous chromosomes are in action

during sexual reproduction.

Chormatids, on the other hand, are two exact copies of DNA that make up each chromosome.

Chromatids are in action during cell division.

3. Forming Reasoned Opinions. How is synapsis important to the outcome of meiosis? Explain.Synapsis is the pairing of homologous chromosomes. Synapsis is important to the outcome of

meiosis because if the pairing did not happen then the proper genes would not get to the

proper places and the offspring would be a clone to one of the parents. If synapsis does not

occur, than the genes would not be aliened in a way that would allow them to transmit

information regarding the trait. In my opinion, the result would be: cloning, deformity, or failure

to continue cell growth.

4. Evaluating Methods. How could you modify your model to better illustrate the process ofmeiosis.

I would make the inside of the cells and the cytoplasm more visible and use more distinct colors

to better see the poles and outlines.

5. Drawing conclusions. How is the process of meiosis similar to those of mitosis? How are theydifferent?

Meiosis is a form of cell division that halves the number of chromosomes when forming

specialized reproductive cells. Meiosis involves two divisions of the nucleus meiosis I and

meiosis II. Before meiosis begins, the DNA in the original cell is replicated.

Mitosis is the process during cell division in which the nucleus of a cell is divided into two nuclei.

Each nucleus ends up with the same number and kinds of chromosomes as the original cell.

6. Predicting outcomes. What would happen to the chromosome number of an organismsoffspring if the gametes for sexual reproduction were made by mitosis instead of by meiosis?

The offspring would have the same amount of chromosomes as the original cell started out

with. Also, I think the offspring would look exactly like one of the two organisms. Since the

chromosomes dont have a piece of the other chromosome.


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7. Further inquiry. Write a new question about meiosis or sexual reproduction that could beexplored with your model.

How many different combinations of chromatids are there before crossing over?

Official Biology Project4-1.

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