le Blog de Jeremy

Learning about the crossing over of DNA in Prophase 1 of Meiosis was hard. Thining back on it, I wish I learned earlier that the crossing over happens between haploid pairs. Haploid pairs are the pairs of chromosomes, one form your father and one from your mother. There are 23 haploid pairs in a human body. The haploid pairs form what is known as a tetrad. I had believed that crossing over could happen between any two chromosomes. This would not work because then some people would be missing important genetic info like how to make protiens. The discussion about Sandra, Mike, and Chris Serbert helped me learn the idea. It showed how no matter what, every sperm, egg, or pollen cell made in Meosis is different.

Jeremy's Blog

I was only in class 3 days this week. One of the two days was spent taking a quiz so we only had two good working days. We finished up with cell reproduction and started on multi cellular reproducrion. We learned that there are 46 chromosomes in a human body. When we reproduce, we give 23 of the 46. By getting half the chromosomes from each parent it makes every person look and act different. If every person got the full DNA from their parents, every person would have double the DNA and would explode from having too much info in their bodies. There are two sex chromosomes out of the 46. X and Y or X and X. If a person has two x's they will be a girl. If a person is a boy they will have an x and y. The other 44 chromosomes are autosomes which control all other things. Anything that differs between boys and girls if found in x and y. The others determine things that doesn't matter between boys and girls like hair and eye color.

Now we started getting into meosis. We started to look at a simulation of meosis. The first things we noticed was that it is almost idntical to mitosis. The biggest difference is meosis makes four cells by dividing twice. The DNA is not replicated inbetween the two divisions so you end up with 4 cells with 23 chromosomes. Before the proccess starts tetrads, or groups of four chromosomes form. In the tetrad some of the genes go the the other side of the tetrad.

In my own reaserch I learned that in meosis sperm and egg cells are formed. The proccess only happens in animals because of this. All of the phases of mitosis are present in meosis. The same things happen in each phase in meosis as in mitosis except Prophase. The difference is each phase happens twice.

It was a bad week in science this week. We had a sub twice in the week and I was absent one of the days the sub was there. We continued with mitosis this week. We talked about how chromosomes change during mitosis and a cell's life. They start as chromatin, and unwoung mess of DNA in the nucleus. Then it condences into a chromosome. Then the chromosome is copied and conected to the copy at a kinetacore. The two chromosomes individualy are now called chromatids, while together they are a chromosome. Then when the two chromatids separate during anaphase of Mitosis, they are each chromosomes again. And in telophase when two nuclei are formed they unwind into chromatin again.

We then learned about the cell cycle. It has four stages. Gap 1, Syntesis, Gap 2, and Mitosis. In Gap 1 the cell does regular things like making protiens and growing. At the end of Gap 1, the cell checks if all the conditions are right to reproduce. If not, it repeats Gap 1, if the conditions are right it moves to synthesis. In synthesis the cell copies all the DNA in it's nucleus. Then it moves to Gap 2 where it grows more in preporation to Mitosis, and it makes any protiens it will need in Mitosis. Now the cell moves to Mitosis where it splits apart to form two daughter cells. Then the cell cycle starts over with Gap 1 in both cells. The lenth of the full cycle varies for different types of cells. A skin cell might take 8 hours to go through the cycle, but a heart cell could take 45 years.

We learned about how much time a cell spends in each phase, Interphase, Prophase, Metaphase, Anaphase, and Telophase. 56% of it's time is in Interphase, 28% in Prophase, 8% in Metaphase, 6% in Anaphase, and 3% in Telophase. So if it takes a cell 24 hours to go through all these, 13.44 hours are spent in Interphase, 6.72 hours in Prophase, 1.92 hours in Metaphase, 1.44 hours in Anaphase, and 0.72 hours in Telophase.

Science First week after Christmas 1/9

This week was kind of awkward because we were discossing reproduction and its difference from sex. The first thing we wanted to do was clarrify the difference between the two things. We only want to learn about reproduction. Reproduction is the sperm meeting with the egg cell. We knew how mammals and some other animals reproduced, but we did not know how cell reproduce. A living thing grows because cells are reproducing. Cells reproducing is the basic part of human reproduction.

We had two theories on how cells reproduce.One theory we had was that cells reproduced with a sperm cell and egg cell. But this didn't make sence because a single cell would not produce a sperm cell and an egg cell just to make one cell. Also, we knew cells reprodused as one not as two, unlike humans. Our other theory was that cells split themselves in half from one mother cells into two daughter cells.

Wecame up with certain things that must happen in cell reproduction.DNA must be copied because otherwise the cells would not look the same and they would each only have half the DNA the original cell had. Another problem was having each cell have all of the organelles such as mitochondria and ribosomes. We thought that that the cell may create double the amount of each organelle it has. The last problem we saw was if a cell splits in half, it makes two cells half the size the origonal. This would cause the organism not to grow. We decided that the cells must grow at some point in their life.

We learned that the Cell does copy its DNA and reproduce in a prosses called mitosis. The steps of mitosis are Prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis. In prophase DNA is copied and the nucleus begins to fade. In Prometaphase the nucleus is gone and there is only chromosomes. Metaphase is when the chromosomes align in the center of the cell. Anaphase is when spindle fibers connect to the kinetochores and start to pull the chromosomes apart from their copies to the poles of the cell. In telophase the chromosomes form two nuclei at the poles of the cell. In the last step cyokinesis, the cell separates into two separate cells.