BIO 130 Cell divisions

Explain 4 different ways chromosome structure can be changed.

-Deletion: a part of a chromosome or a sequence of DNA is missing -Duplication: chromosome is duplicated or replicated, resulting in multiple copies of that region. -Inversion: A defect in the chromosome in which a segment of the chromosome breaks off and reinserted in the same place but in the reverse direction relative to the rest of the chromosome. -Reciprocal translocation: chromosome abnormality caused by rearrangement of parts between nonhomologous chromosomes.

If you start mitosis with 126 chromosomes, how many should you have in the resulting daughter cells?

126, exact copies

How are deletions and duplication related?

A chromosomal deletion takes place when information that is swapped between homologous chromosomes is not equal. Normally, homologous chromosomes cross-over and exchange genes for the same traits. Sometimes one of the chromosomes accepts the gene from its partner, but does not transfer its gene. This leaves one chromosome with a duplication of a gene and the other with a deletion.

Centrosomes (centrioles) are not found in plants. Explain.

A plant cell does not have centrioles that form the centrosome organizational centers. They use the MTOC's or microtubule organizational centers instead. These are found at different places in the cytoplasm of the cell.

What happens when the myeloid blood cell line is compromised in this condition (above)?

A result of this Philadelphia chromosome is myelogenous leukemia. The banding pattern shows that parts of chromosomes #9 and #22 have been exchanged. Myeloid blood cells are the line of stem cells that give rise to red blood cells, platelets and some white blood cells. When this line of cells is affected it can result in a wide range of problems. White blood cells fight infection. Almost half of newly diagnosed patients will have no symptoms, and the disease will be detected by an elevated white blood cell count on a routine blood test. Later an increased numbers of white blood cells may be abnormal in shape and function leading to a compromised immune system. The most common symptoms are a result of a low red blood cell count (anemia) and an enlarged spleen (splenomegaly). Anemia leads to fatigue, shortness of breath with activity because there are not enough normal red blood cells to carry oxygen to body cells. Splenomegaly causes abdominal fullness or discomfort, feeling full early when eating (the spleen is pressing on the stomach) and weight loss. Bone pain, fever, sweats and fatigue are other symptoms that may appear early on.

What is cytokinesis? What is karyokinesis? When do each take place in the life of a cell?

After mitosis, an event called cytokinesis takes place, where the cell divides. Cytokinesis is the actual cell division. Mitosis can also be given the name karyokinesis. The term 'kinesis' found in both terms refers to dividing. However, if you remember karyo refers to the nucleus or at least the DNA inside the nucleus. So karyokinesis is dividing up the DNA (chromosomes) and cytokinesis is dividing up the cytoplasm of the cell which includes all the organelles and other stuff in the cell - this is where the cell is actually split.

How could non-disjunction lead to Down syndrome?

An example of a trisomy is seen in the karyotype of an individual with Down syndrome. The karyotype has pairs of homologous chromosomes, except when you look at #21. It has 3 chromosomes instead - this is where it gets the name trisomy #21. Some of these mutations might lead to machinery for cell division malfunction. Some of these malfunctions lead to non-disjunction and thus the aneuploidy conditions that result, such as Down syndrome.

When does independent assortment take place during meiosis? Explain it.

Another event that produces variations is called independent assortment. This event actually take place in meiosis I. When the homologous pairs are attached to the spindle there is no particular way that pairs are "grabbed" by the spindle fibers. At metaphase I, the alignment is random. The maternal and paternal chromosomes do not have to be lined up on one side or the other. They will be aligned randomly.

Describe how the animal cell accomplishes cytokinesis.

Beneath the membrane there is a contractile ring made of microfilaments. They're like the cytoskeleton components used to contract muscle. Here they are used to contract the center of the cell and pinch it into two cells. This happens toward the end of mitosis after the DNA (chromosomes) has been separated. This way, each cell gets the instruction before the cell divides. The resulting cells are called daughter cells.

What is binary fission? Is this asexual or sexual? Who uses this process for cell reproduction?

Binary fission is the only way that prokaryotic cells can reproduce. Prokaryotes do not do sexual reproduction. This process begins with making a copy of the DNA of the cell. After a copy of the DNA has been made the cell elongates and separates the copies - each copy of DNA is anchored such that as the cell gets longer the DNA is separated. Finally, the cell makes a new cell wall in the middle of the elongating cell to separate the cell into two. Sometimes the two new cells will stay attached to each other, other times they will separate and go their own way.

Distinguish asexual and sexual reproduction. Give an example of each.

Cells reproduce by asexual or sexual reproduction. Asexual reproduction is where new cells or offspring are produced by a single parent. In this case one parent cell duplicates to produce a clone (offspring). Sexual reproduction involves producing offspring by two parents where the parent cells (called gametes) fuse to form one fertilized cell or zygote (offspring). This is different from asexual reproduction, the resulting cells are unique and do not look exactly like the parent cell.

What are centrioles or centrosomes and what are they used for during cell division in animal cells?

Centrioles migrate to the opposite poles of the cell. The pairs of centrioles become organizational centers called centrosomes. They're use for splitting the sister chromatids.

What two events within meiosis give us variation? What process outside of cell division increases the potential of variation?

Crossing over and independent assortment give us variation. Our environment can increase the potential of variation.

Where are the instructions for our characteristics found in the cell?

DNA

Who crosses over and what is exchanged? What is a chiasma?

During crossing-over, the paternal and maternal non-sisters will cross over at different points called chiasma. These points of crossing over are where genetic information can be swapped. When pairs are later separated they each take with them a piece of their homologous. This is normally an even swap. They would never swap an eye color gene for a coat color gene - the swap would not be even and both chromatids would be lacking genes as a result.

When you look at a diploid karyotype you can see that chromosomes come in pairs. What are these pairs of chromosomes called?

Each piece of DNA must make a copy or sister chromatid. The copies are then separated to different ends of the cell before the cell splits. This ensures that each cell has a copy.

In alteration in chromosome structure, why could it be dangerous to move a gene to a different location?

Genes can get swapped and in the process place genes in the wrong location. This is called an inversion. This can be a serious result because most genes are under some kind of control. Some genes may be used often to make a protein in the cell, other may be used infrequently. How often a gene is transcribed into a protein is control by other regulatory genes. If a gene is moved, it may come under different controls which change how often it gets transcribed and translated into a protein. Too much or too little of a particular protein may be detrimental to a cell.

What events in meiosis I are not part of meiosis II?

Homologous pairing and crossing over

Define homologous chromosomes. How are these different from sister chromatids?

Homologous pairs are non-sister chromosome pairing. They are the same size, have the same centromere position and may have similar banding patterns. Homologous pairs of chromosomes have one maternal pair and one paternal pair. When we see these pairs we know that they came from a diploid cell - one set from maternal and one from paternal. -Sister chromatids may be identical, but not homologous pairs. They're lined together by a centromere. They are similar because they carry genes for the same traits.

Which sex chromosome is necessary for the survival of the developing zygote (fertilized egg)?

However, a trisomic condition that results in XYY produces a normal male. This is probably because the Y chromosome is very small and carries genes that have nothing to do with development. However, notice that if there is an abnormal number, if the Y is present the child will be male. If a trisomic condition results in XXX, the female is normal. This is because in a female, X chromosomes that are not needed can be inactivated.

Why do we make copies of our DNA?

If a cell divides before its DNA is duplicated, then only one cell gets all the DNA. Each piece of DNA must make a copy or sister chromatid. The copies are then separated to different ends of the cell before the cell splits. This ensures that each cell has a copy. Humans must make copies of all 46 pieces of DNA before a cell can divide.

Why is variation in a population important?

If everyone is the same then a deadly plague can kill us all, because out immune system is exactly alike.

What happens to a diploid karyotype when you remove one member of each pair?

If one set of the chromosomes is removed. The cell becomes a haploid.

Distinguish polyploidy from aneuploidy. Diploid is the normal condition in animals. What is triploidy and tetraploidy referring to?

If the change results in different numbers of sets it is referred to as polploidy. For example, some plants have 3 sets of chromosome - triploidy. The commercial banana plant and other plants have this condition resulting in the seedless varieties seen in our grocery. This means they are 3n instead of the normal 2n (diploid). Other organisms can have even more sets of chromosomes. For example, 4n is a tetraploidy condition.

What happens during non-disjunction of Meiosis I? Meiosis II?

In meiosis I of this example, one of the pairs of chromosomes is not separated and both members of the pair go to the same side of the cell. This results in a daughter cell with too many chromosomes and one with too few. After meiosis II, the resulting gametes all have either too many or too few chromosomes. Meiosis I took place as normal, but there was a non-disjunction in meiosis II. The sister chromatids of one chromosome did not separate leading to one daughter cell with an extra chromosome and one with too few. The other cell divided normally to give the correct number.

What is synapsis and how does it lead to crossing-over?

Instead of single chromosomes like mitosis in prophase, the chromosomes pair up with their homologous. Homologous pairs come together in an event called synapsis. Then, when they are very close, the non-sister homologous appear to entwine with each other in an event called crossing over.

Summarize each phase of meiosis I:

Interphase: G1, S, G2 Prophase: chromosome condensed into chromatins, nuclear envelope disassemble, spindle apparatus created, chromosomes pair with their homologous pairs (synapsis), non-sister homologues entwine with each other (crossing over), each centrioles move to opposite poles Metaphase: chromosome lined up in the middle as homologous pairs Anaphase: homologues pairs are pulled apart by the spindle apparatus to opposite poles Telophase: chromosomes de-condensed, nuclear envelope forms around each set of chromosomes, spindle apparatus disappear, 2 new haploid cells created

Is mitosis or meiosis responsible for the tremendous variation among humans? Explain.

Meiosis is responsible for variation among humans.

Compare the cells that result from mitosis and meiosis. How are they different? Why don't we all produce gametes by mitosis?

Mitosis are exact copies of the mother cell and diploid. Mitosis must be exact copies to function properly and replace the old ones. Meiosis are variation cells of the maternal cell and paternal cell. They are are haploid. Gametes are for fertilization, therefore they only need one set of chromosomes.

What is the purpose or "goals" of mitosis?

Mitosis is important for the growth of all organs systems include the lengthening of bones and muscle to gain height. At some point this vertical growth stops and the human body just maintains. This means making repairs or replacing old worn out cells with new ones. Some cells continue to do this throughout our lifetime. For example, skin cells are constantly shed and replaced.

What kind of chromosomal abnormalities can lead to spontaneous abortions or developmental defects?

Physical and chemical changes in the cell can damage chromosomes structurally or alter their number in the cell. Chemical exposure can lead to errors in meiosis leading to changes in chromosome number. When serious alterations are made in the cells of a developing embryo it can lead to spontaneous abortions. It may happen so early in development that a mother never realized that they were pregnant. There are other times that individuals develop full-term and are born with these chromosomal abnormalities exhibiting various developmental defects.

Describe how the plant cell accomplishes cytokinesis.

Plants do not use contractile rings to divide their cells. This is because they have a rigid cell wall. Instead they form a cell plate on which new walls. It begins with the appearance of large vesicles along the equator of the cell. These vesicles converge to form a cell plate. The cell plate is a structure on which new cell wall can be laid down. After the wall is assembled, cytokinesis is complete. These cells stick to each other as seen in plant tissues that are growing.

When does mitosis take place in a cell cycle? Name its phases.

Prophase, Metaphase, Anaphase, Telophase

Which one of these two processes gives variation to populations of organisms?

Sexual reproduction

What is a chromosome? What are sister chromatids and how are they attached?

Sister chromatids are the copies of a piece of DNA. They are held together by another structure in the middle called a centromere.

Relate each of the following terms: mitosis, meiosis, zygote, adult, diploid, haploid, gamete, fertilization. Use all of the terms to describe a human life cycle.

Starting with the first cell produced at fertilization, called the zygote. The zygote will grow. This kind of growth is due to the addition of new cells by a process called mitosis. Mitosis is asexual reproduction because it need to make the same kind of cells. The new zygote will divide by mitosis to produce more cells until it has become a multicellular structure. At some point the cells begin to differentiate from each other - some destined to be skin or nerve cells, muscle, bone, and etc. This part of the process is called development and allows the multicellular structure to take on shape, create organs and organ systems. After birth, an infant will continue to grow by mitosis into an adult. At adolescence, germ cells called sex cells are produced. This takes place in the gonads. For a female it takes place in the ovaries and for males it is in the testes.To make our sex cells or gametes we do a process called meiosis. It is different because the new gametes must all be different from each other. Meiosis is part of sexual reproduction. They must also have half the number of chromosomes. This can only be accomplished by the process of meiosis. Gametes for a female are the eggs and for the male they are the sperm. At fertilization, a sperm and egg fused their DNA (chromosomes) together and produce a zygote.

What are genes? Where are they located?

The DNA contains segments of information called genes that code for different proteins that carry out tasks and give us our characteristics such as eye color or height.

Women are advised to have babies before the age of 35, if possible, but no such advice is usually offered to men. Why the difference?

The age of female eggs is said to be as old as the individual herself. Females have all the eggs they will ever have at birth. So if a woman is 35 years old, her eggs are said to be the same age. As a female ages, more mutations can accumulate in various cells, including egg cells. Some of these mutations might lead to machinery for cell division malfunction. Some of these malfunctions lead to non-disjunction and the aneuploidy conditions that result, such as Down syndrome.

What is a cell cycle? What are the major phases of a cell cycle?

The cell cycle, or cell-division cycle, is the series of events that take place in a cell leading to its division and duplication that produces two daughter cells. - The major phases of a cell cycle: Interphase, Prophase, Metaphase, Anaphase, Telophase

What creates the Philadelphia chromosome? What condition does this result in?

The fourth type of alteration to chromosomes is called a translocation. These kinds of structural alterations take place between non-homologous chromosomes. Sometimes during crossing-over two non-homologous chromosomes swap genes. This leads to the placement of genes in often distant locations. This translocation takes place between chromosome #9 and #22. It results in a short chromosome called the Philadelphia chromosome. Chromosome #22 has been severely reduced in size. It also places a cell division gene from #9 onto the end of #22. This gene becomes overactive because it is under different controls. This lack of control activates it as a cancer-causing gene.

What are kinetochores and how are they different from centromeres?

The kinetochore is the protein structure on chromatids where the spindle fibers attach during cell division to pull sister chromatids apart. The centromere is the part of a chromosome that links sister chromatids. During mitosis, spindle fibers attach to the centromere via the kinetochore.

Describe interphase. Name its periods and what happens in each.

The longest phase is called interphase. It's the period the cell is not dividing. It is doing normal cellular activities. This phase can be subdivided into periods: G1, S and G2. The first period, G1, is a growth phase. Although the G stands for gap we can use it to remember that the cell is growing in size or enlarging. The S (synthesis) period is when the DNA of the cell is being synthesized. This means that the cell is busy making a duplicate or copy of all 46 pieces of DNA. These copies are held together and referred to as sister chromatids. The G2 period is another growth period, but this time activities involve preparing for cell division. During G2, the cell duplicates the centrioles because it will need two pairs to help divide up chromosomes.

Characterize Turner syndrome. Is this a monosomic or trisomic condition? Are these males or females?

The monosomic condition XO results in a female with Turner syndrome. The O means that there is no other chromosome.

Some cells stop their cell cycle and specialize. For example nerve cells no longer replicate after development. Why is this important?

The nervous system stops making new cells when it has enough. It would not be good to continue making nerve cells in the brain, as there would not be enough room to accommodate all the new cells. These cells are not readily dying during development.

What is the purpose of meiosis?

The purpose of meiosis is for making gamete cell. They must be haploid and have variation, because the other set of chromosomes will be present when it is fertilized.

Characterize Klinefelter syndrome. Is this a monosomic or trisomic condition? Are these males or females?

The trisomic condition that results in XXY produces a male with Klinefelter syndrome.

What does "2n" mean? Explain. What does "n" mean? Explain.

The zygote has 2 sets of chromosomes for a total number of 46 (2n=46). 2 sets is referred to as a diploid cell. One set (n) is called a haploid cell. Gametes are the only cells that are referred to as haploid. The human haploid number is 23 (n=23). So this means that all human cells are diploid except for the gametes that are produced by meiosis.

What is an aneuploidy individual? Distinguish a monosomic from a trisomic condition. Which one is found in Down's syndrome?

There are different conditions that result from an abnormal chromosome number called aneuploidy. Some different types include zygotes having on extra chromosome indicated as 2n + 1. This results in a trisomic condition. If the zygote has one less chromosome indicated as 2n - 1, the result is a monosomic condition.

Describe the formation of the spindle apparatus. What exactly are spindles and what are they used for?

There are microtubules that are extending from these centrosomes. They build and organize a spindle apparatus. Each extending microtubule will pierce a chromosome. This is close to the center of the chromosome where sister chromatids are attached at the centromere. However, the microtubule fibers do not pierce the centromere. They attach to a structure along the outside called the kinetochore. The spindle fibers are attached to the chromosomes from opposite poles of the cell, the fibers can then arrange the chromosomes by moving them around. They pull the sister chromatids apart during mitosis.

What are the autosomal chromosomes? What are the sex chromosomes?

There is a total of 46 chromosomes in the human cells. The chromosomes have been arranged in pairs. The first 22 pairs are called autosomal chromosomes. The last or 23rd pair is the sex chromosomes.

Summarize Interkinesis:

This is a very short interphase where the cell gets prepped for the next division. This does not involve the DNA duplicating because we are still in the middle of trying to separate the DNA from the last cycle. G1 and G2

What kinds of abnormalities are brought about by non-disjunction?

When damage occurs to the machinery of a cell that controls cell division, it results in changes in chromosome number. This leads to a non-disjunction or non-separation of chromosomes.

How is DNA packaged when the cell is at rest (i.e., not actively dividing)?

When the cell is not dividing, the DNA is wound up around proteins called histones into unit called nucleosomes. These units are then loosely wound into thin fibers that we call chromatin. This is how it sits in the nucleus of the cell. Chromatin is simply an organized strand of DNA. The cell can get to the information by unwinding a segment of information or gene, transcribing the instruction and winding it back up. It does not need to unwind all the DNA to get to one gene.

How is DNA packaged when the cell is actively dividing?

When the cell makes a copy of its DNA and moves it into a new cell it will "package" the DNA into a more compact form. The chromatin fibers are coiled up very tight into a structure called a chromosome. This requires the help of other proteins to help wind and stabilize the chromosome. So we say that chromatin is condensed into a chromosome. The chromosome (DNA copy) can easily and efficiently moved into a new cell.

If we all start out as a single cell that is replicated millions of times, why don't all cells look alike?

each type of cells have their own function

What does independent assortment lead to?

incredible variations that are possible in our gametes

What is the origin of each member of a pair of chromosomes? (i.e., where did each come from?)

maternal and paternal parents

Which division, meiosis I or II is most like mitosis?

meiosis II

Do we ever refer to homologous chromosomes in the process of mitosis? Explain.

no, the chromosomes don't need to be pairs with their homologous chromosomes during mitosis

Summarize each phase of meiosis II:

same as mitosis, end products are 4 haploid cells

Are homologous chromosomes present during mitosis? Explain.

yes, homologous chromosomes are present during mitosis