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Station 5 Nondisjunction is the failure of two members of a homologous pair of chromosomes to separate during meiosis. It gives rise to gametes with a chromosomal content that is different from the norm. The consequences of this are usually quite severe, and a number of clinical conditions are the result of this type of chromosome mutation. 1. Define Nondisjunction. 2. Use the diagram to describe what happens during meiosis that results in Klinefelter’s male. 3. Use the diagram to describe the process that occurs in meiosis that results in an XYY male. Station 6 In the diagrams below, label each stage of meiosis on your answer sheet using the following terms: Prophase I, Prophase II, Metaphase I, Metaphase II, Anaphase I, Anaphase II, Telophase/Cytokinesis I, Telophase/Cytokinesis II Station 7 In the table below, label each stage of meiosis on your answer sheet using the following terms: Prophase I, Prophase II, Metaphase I, Metaphase II, Anaphase I, Anaphase II, Telophase/Cytokinesis I, Telophase/Cytokinesis II **terms may be used more than once or not all all** Name of Phase Description 1. Homologous chromosomes pair up and form tetrad 2. Spindle fibers move homologous chromosomes to opposite sides 3. Nuclear membrane reforms, cytoplasm divides, 4 daughter cells formed 4. Chromosomes line up along equator, not in homologous pairs 5. Crossing-over occurs 6. Chromatids separate 7. Homologous line up alone equator 8. Cytoplasm divides, 2 daughter cells are formed Station 8 On the lines provided on your answer sheet, order the different stages of meiosis I THROUGH meiosis II, including interphase in the proper sequence. 1. _____________ 2.______________ 3. _____________ 4. _____________ 5.______________ 6. _____________ 7.______________ 8. _____________ 9.______________ homologous chromosome line up in the center of the cell spindle fibers pull homologous pairs to ends of the cell 4 haploid (N) daughter cells form cells undergo a round of DNA replication sister chromatids separate from each other 2 haploid (N) daughter cells form spindle fibers attach to the homologous chromosome pairs individual chromatids move to each end of the cell crossing-over (if any) occurs Station 9 Haploid & Diploid Background Information All animal cells have a fixed number of chromosomes in their body cells which exist in homologous pairs (2n). Each pair of chromosomes consists of one chromosome from the mother and the second from the father. During the process of meiosis, the sex cells divide to produce "gametes" which then contain only one set of the chromosomes (n). When the male gamete (sperm) and the female gamete (egg) fuse during fertilization and zygote formation, the chromosome number is restored to 2n again. Thus, diploid cells are those which contain a complete set (or 2n number) of chromosomes whereas haploid cells are those that have half the number of chromosomes (or n) in the nucleus. Gametes (sperm and egg) are haploid cells and somatic cells are diploid. The number of chromosomes (n) differs in different organisms. In humans a complete set (2n) comprises of 46 chromosomes. Haploid cells are a result of the process of meiosis, a type of reduction cell division in which diploid cells divide to give rise to haploid cells. During meiosis, a diploid cell divides to give rise to four haploid cells in two rounds of cell division. 1. What is the difference between a haploid and diploid cell? 2. For each of the following state if the cell is haploid or diploid. Sperm cell = Liver cell = Egg cell = Stomach cell = 3. If the diploid number in a liver cell is 52, how many chromosomes are there in the egg of this organism? 4. The combination of a _______ and an ______ produces a zygote with 46 chromosomes. 5. Meiosis produces haploid reproductive cells called ___________________. 6. Name the 2 human gametes & tell their chromosome number. Station 10 What’s the difference between sister chromatids and homologous chromosomes? Sister chromatids are (mostly) identical! It’s basically a copy (“replicate”) of the original chromatid. Homologous chromosomes only share the same size and shape – they may contain the same genes, but they may or may not be the same version in each chromosome of the pair. One comes from the father and one from the mother. Crossing over occurs between these (NOT between sister chromatids). 1. Draw a picture that shows the difference between a chromosome, sister chromatids, and homologous chromosomes. Station 11 Use the DNA Fingerprints below to answer the questions in the boxes. dad 1 baby dad 2 mom Lt. Russ is investigating a murder scene. The felon was scratched by his victim & some of his skin cells were found under the victim’s fingernails. A DNA test was performed. Which of the suspects is the murderer? felon Mrs. Smith has a baby named Jessica. She believes one of two men can be the father of her child. A paternity test is done and the results are shown above. Which of the 2 men are Jessica’s father? S1 S2 S3 Station 12 Gel Electrophoresis Before DNA can be analyzed with gel electrophoresis, restriction enzymes must be applied. Restriction enzymes work like “molecular scissors” cutting the long DNA molecules at different locations. Where they cut depends on the code within the DNA molecule and the code within the enzymes. For example, one type of enzyme cuts DNA wherever it encounters a sequence AGCTT. The length of these fragments will vary from person to person because the code for every person’s DNA is different. Some fragments will be long, others short. After DNA is cut using restriction enzymes, it is micropipetted into a well within an agarose gel. Agarose gel is a thick, porous, Jell-O like substance. It will act as a molecular strainer, allowing smaller pieces of DNA to move through it more easily than larger pieces. The agarose gel containing the DNA samples is placed in an electrophoresis chamber. The DNA fragments have a slight negative charge so they move toward the tray’s positive end. Smaller DNA fragments travel further toward the tray’s opposite end than do larger DNA fragments. When electrophoresis is complete, the fragments are distributed in the gel according to their lengths. 1. What do restriction enzymes do to the DNA? 2. What is agarose gel and how does it work? 3. Where is the DNA placed in the gel electrophoresis apparatus? 4. How does electrophoresis work? Station 13 DIHYBRID CROSSES STEP 1: Determine what kind of problem you are trying to solve. STEP 2: Determine letters you will use to specify traits. STEP 3: Determine parent’s genotypes. STEP 4: Make your punnett square and make gametes STEP 5: Complete cross and determine possible offspring. STEP 6: Determine genotypic and phenotypic ratios. EXAMPLE A tall green pea plant (TTGG) is crossed with a short white pea plant (ttgg). TT or Tt = tall GG or Gg = green tt = short gg = white tg tg tg tg TG TtGg TtGg TtGg TtGg TG TtGg TtGg TtGg TtGg TG TtGg TtGg TtGg TtGg TG TtGg TtGg TtGg TtGg A tall green pea plant is crossed with a tall white pea plant ___________ X ___________ ____ Tall/Green : ____ Tall/White : ____ Short/Green : ____ Short/ White Station 14 DIHYBRID CROSSES In mice, the ability to run normally is a dominant trait. Mice with this trait are called running mice (R). The recessive trait causes mice to run in circles only. Mice with this trait are called waltzing mice (r). Hair color is also inherited in mice. Black hair (B) is dominant over brown hair (b). A heterozygous running, heterozygous black mouse is mated with a homozygous running, homozygous black mouse. What are the possible genotypes and phenotypic ratios? ____________ X ____________ Station 15 SEX-LINKED TRAITS BACKGROUND INFORMATION: Sex-linked traits are those whose genes are found on the X chromosome but not on the Y chromosome. For each of the genes that are exclusively on the X chromosomes, females, who are XX, would obviously have two alleles. Males, who are XY, would have only one allele. Thus females with one recessive allele and one dominant allele, for a gene that is unique to the X chromosome, will always display the dominant phenotype. However, a male with a recessive allele for a gene unique to the X chromosome will always exhibit that recessive trait because there is no other corresponding allele on the Y chromosome. Use the information below to answer the following questions. XH- X chromosome with normal dominant allele (no hemophilia) Xh - X chromosome with recessive hemophilia allele Y - Y chromosome (does not contain comparable gene) XB - X chromosome with normal dominant allele (not colorblind) Xb - X chromosome with recessive colorblind allele Y -Y chromosome (does not contain comparable gene) PROBLEM 1. A normal-sighted woman, who has a colorblind father, marries a colorblind man. What is the probability that they will have a son who is colorblind? What is the probability that they will have a colorblind daughter? Complete the Punnett square. 2. What is the probability that a colorblind woman who marries a man with normal vision will have a colorblind child? Complete the Punnett square. Station 16 KARYOTYPE 1. How many pairs of autosomes does this karyotype have? 2. How many pairs of sex chromosomes does this karyotype have? 3. What do you notice about the X and Y chromosomes? 4. What is the sex of this organism? 5. Looking at all of the pairs, do you see any different circumstances? What is the special circumstance that you find? 6. What kind of effect do you think this abnormality on chromosome pair #21 will have on the organism? Station 17 KARYOTYPE 1. What is the sex of this organism? 2. Are there any trisomy’s in this karyotype? If so, which chromosome pair is a trisomy? 3. What would you expect to see in the number of genes on chromosome 18? Station 18 Diabetes and Genetics In Type 1 diabetes, the body does not produce insulin. The body breaks down the sugars and starches you eat into a simple sugar called glucose, which it uses for energy. Insulin is a hormone that the body needs to get glucose from the bloodstream into the cells of the body. Type 1 and Type 2 diabetes have different causes. Yet two factors are important in both. You inherit a predisposition to the disease then something in your environment triggers it. Genes alone are not enough. One proof of this is identical twins. Identical twins have identical genes, yet when one twin has type 1 diabetes, the other gets the disease at most only half the time. In most cases of type 1 diabetes, people need to inherit risk factors from both parents. It seems that these factors must be more common in Caucasians because they have the highest rate of type 1 diabetes. Because most people who are at risk do not get diabetes, researchers want to find out what the environmental triggers are. Some are believed to be cold weather and viruses. Type 1 diabetes is generally considered to be an autoimmune disorder. Autoimmune disorders occur when the immune system attacks the body's own tissues and organs. For unknown reasons, in people with type 1 diabetes the immune system damages the insulinproducing beta cells in the pancreas. Damage to these cells impairs insulin production and leads to the signs and symptoms of type 1 diabetes. Type 2 diabetes is non-insulin–dependent diabetes, and usually is caused by genetic predisposition to insulin receptors malfunctioning when other risk factors are present like obesity, lack of exercise and poor diet. Feedback Loops Homeostasis in the body is maintained by internal feedback mechanisms called negative feedback. Negative feedback returns a system to a set point once it deviates sufficiently from that set point. This is how blood glucose levels are controlled. The pancreas has a crucial role in the production of the hormones insulin and glucagon which work together to maintain homeostasis. When blood glucose levels are high, the pancreas releases insulin. Insulin signals body cells to accelerate the conversion of glucose to glycogen, which is stored in the liver. When blood glucose levels are low, glucagon is released from the pancreas. Glucagon binds to liver cells, signaling them to convert glycogen to glucose and release the glucose into the blood. Glucose Regulation In the following illustration use the phrases found in the word bank to show the feedback loop described on the previous page. *Glucagon secreted from pancreas *Blood glucose decreases; insulin secretion inhibited *Glycogen forms from glucose *Blood glucose increases; glucagon secretion inhibited *Insulin secreted from pancreas *Glucose forms from glycogen