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Major Events Of The Cell Cycle

Describe how major events of cell division that enable the genome of one cell to be passed on to two daughter cells. List the phases of cell cycle and describe the sequence of events that occurs during each phase. There are two main stages of the cell cycle, with multiple subdivisions within each. Interphase is the first stage, and it’s composed of G1 (contents of the cell are duplicated sans the chromosomes), S (chromosomal duplication), and G2 (checkpoints) phase.

After interphase, there is the mitotic phase. The mitotic phase is composed of mitosis (division) and then cytokinesis (division of cytoplasm=2 daughter cells). The cell cycle ultimately produces two daughter cells. These processes allow the (complete) genetic material present in a cell/organism to be passed on to the daughter cells of cell division. The phases of Interphase ensure this for example. During the S phase, DNA is duplicated, aka 46 chromosomes.

This allows the cells to split so they can have equal amounts of genetic material which are passed on to the daughter cells. The phase of G2 has cell checkpoints to ensure not errors occurred in the duplication process. After the volume is doubled, the cell undergoes the mitotic phases. Under these processes the cell will divide which will result in the genome of one cell being the same for the daughter cells. Explain how the abnormal cell division of cancerous cells differs from normal cell division.

Cancer cells can divide without any regulation for various reasons, for example they can pass checkpoints (which monitor errors made in cell cycle processes) which allow the mutation to occur and for abnormal cell division to follow. A normal cell will undergo these checkpoints to ensure the cell material was copied correctly. Even when they are not growth factors present any longer, cancer cells will not stop dividing, opposed to normal cell division. List the phases of meiosis I and meiosis II and describe the events characteristic of each phase.

Describe the process of synapsis during prophase I and explain how genetic recombination occurs. In meiosis I, there is prophase I (this is where synapsis occurs, crossing over is also possible between pairs during this phase, the centrosomes will move to the poles of the cell, the nuclear membrane will dissolve as well, the chromosomes will condense, spindle formed) , metaphase I (the homologous pairs of chromosomes line up at the center of the cell), anaphase I (the chromosomal pairs are separated, move to opp. poles), and telophase I (division finished, nuclear membrane reappearance).

Meiosis II, there is prophase II (similar to prophase I, except no crossing over and synapsis), metaphase II (the chromosomes line up at the center as well), anaphase II (the chromosomes separate into chromatids), and telophase II (nuclei formed for 4 daughter cells, haploid chromosome # in each daughter cell). Meiosis I results in 2 haploid cells while meiosis II results in 4 haploid cells. Synapsis is when chromosomal pairs, at the start of meiosis in prophase I, fuse/pair so that the genetical material in each is rearranged, crossing over.

So that leads to genetic recombination since the genetical material is spread amongst the chromosome pairs which leads to a greater chance of offspring with different traits than their parents. Describe the key differences between mitosis and meiosis. Explain how the end result of meiosis differs from that of mitosis. Mitosis results in 2 diploid cells, while meiosis results in 4 haploid cells. Mitosis is asexual reproduction; ex. Produced body cells). While Meiosis is sexual reproduction that results in gametes. There is only one division in mitosis, while in meiosis there are 2 divisions.

Synapsis occurs during meiosis (prophase I), but not in mitosis. Crossing over rarely occurs in mitosis but happens frequently in meiosis (to ensure genetic recombination). Explain how independent assortment, crossing over, and random fertilization contribute to genetic variation in sexually reproducing organisms. All these processes contribute to genetic variation. Crossing over occurs during prophase I of meiosis I. Genetic material is rearranged between homologous chromosome pairs. This leads to genetic recombination because genetic information from both parents can be contained in one chromosome.

Independent assortment also contributes to genetic variation because chromosome pairs can arrange in any way during metaphase (of meiosis), allowing for genetic variation to occur because any two chromosomes can rearrange genetic information. Random fertilization refers to the fact that any sperm can fertilize any random egg, ensuring genetic variation. Mendelian and Basic Genetics List several features of Mendel’s methods that contributed to his success including a large sample size. What is Mendel’s law of segregation and law of independent assortment? Mendel chose the peas because of their variety for many different characteristics; ex.

Pod shape, pod color, etc. Peas also produced plentiful offspring which lead to a larger sample size. The characteristics that had larger sample sizes tend to adhere to his predicted ratio (3:1) of dominant and recessive phenotypes being expressed. Mendel’s law of segregation was that two alleles for the same gene are distinct from another during their (gamete) formation. These end up in different cells. The law of independent assortment submits that pairs of alleles segregate during their formation, independent of other alleles’ segregation. Give an example of complete dominance, incomplete dominance, and codominance.

Explain each. For their genotypes, they will always possess a dominant allele, but how they are expressed for their phenotype is different. If the dominant trait for a dog breed’s coat color was Black (B) and brown was recessive (b), complete dominance would be a dog having a BB genotype while having their phenotype being black. Incomplete dominance is when no allele is dominant over the other one, which means they are both expressed for the phenotype. Snapdragon flowers are an example. Breeding a white (rr) and red (RR) flower would result in a pink (Rr) flower. Codominance is when both alleles are present for the phenotype.

An example of codominance is AB blood, because the person has both the A and B allele (being expressed). Define and compare linked genes and sex-linked genes. Explain why the inheritance of linked genes is different from independent assortment (in other words, why do linked genes not assort independently). Explain why the fruit fly is a good experimental organism. A locus is the location of a gene on a chromosome. The closer genes are, there is a lower chance for genetic recombination. Linked genes have their locus close together on a chromosome, so they can be inherited together, instead of assorting independently.

Sex-linked genes are the genes that are on either the X or Y chromosome. An example would be hemophilia. The fruits flies breed quickly and produce a lot of offspring. They only have 8 chromosomes as well, and their traits are easy to distinguish. Distinguish between parental and recombinant phenotypes. Explain how crossing over can unlink genes. Define a map unit. Parental phenotypes is when their traits are observed in their offspring (they express the same traits/phenotype), while recombinant phenotypes are the opposite. It means that the traits of a parent are not observed in the offspring’s phenotype.

A map unit can measure the genetic linkage of certain traits because it measures the distance of genes on one chromosome. Describe the inheritance patterns and symptoms of color blindness and hemophilia. Explain why sex-linked genes are more common in human males. Sex-linked genes are more common in human males because they only inherit one X chromosome from their mother (since they inherit the Y from their father). Hemophilia is a sex-linked recessive gene. The genotypes of a male and female would be: XhXh or XhY (assuming h represents the recessive allele for hemophilia).

Females can be carries, but men cannot (they’re either afflicted or not, since they only have one X chromosome). Hemophiliacs lack certain proteins that are required in order for blood to clot. Color blindness is also a sex-linked disorder. It is also a recessive trait. One of the more common forms of color blindness is red-green colorblindness. This means they have difficulty recognizing these colors from another. The genotype would be similar to hemophilia, except substitute the allele for color-blindness. Human Genetics

Distinguish among nondisjunction, aneuploidy, trisomy, triploidy, monosomy, and polyploidy. Explain how these major chromosomal changes occur and describe these consequences. Nondisjunction is when homologous chromosomes do not separate during the division process, which means their is an abnormal distribution of chromosomes in the daughter cells. Aneuploidy can be caused by nondisjunction, along with the other conditions, which means their is an abnormal number of chromosomes in a daughter cell; aka there is an extra or missing chromosome in the cell.

Trisomy instead of 2 copies of a chromosome, there are three; this can lead to many different defects. Triploidy is very rare, but it is when there is an additional set of chromosomes (instead of 46, =69). Monosomy is when there is a missing chromosome. Polyploidy is when there are more than two sets of chromosome in a cell (numerical change in whole set). Distinguish among deletions, duplications, inversions, and translocations. Define a point mutation. Distinguish between base-pair substitution and base-pair insertions.

A point mutation refers to mutation in which a single base pair (nucleotide) has been changed in DNA. A base pair substitution is when one nucleotide has been replaced by another nucleotide, while base pair insertion is when a nucleotide is added in addition (more in the sequence). Deletions are the when sections of chromosomes are lost, duplications are when certain sections are duplicated, translocations are when chromosomes (non-homologous) rearrange information from certain sections of the chromosome, and inversions are are when sections are inverted (flip/backward).

Describe the type of chromosomal alterations implicated in the following human disorders : Down syndrome, Klinefelter’s syndrome, triple-X syndrome, Turner’s syndrome, XYY. Down syndrome: trisomy (21), Klinefelter’s syndrome (XXY, there is an extra Y chromosome), triple-X syndrome (XXX, 2 barr bodies), Turner’s syndrome (X, females only have 1 X chromosome), XXY (extra y chromosome). Describe the genetic conditions and mode of transmission for : PKU, sickle cell anemia, cystic fibrosis, Tay Sachs, and Huntington’s disease. PKU is a defect where phenylalanine (amino acid) builds up in the body, mutation in gene coding.

It can lead to mental retardation. It is inherited as an autosomal recessive trait, meaning that two copies of the genes had to be present for the condition to occur). Sickle cell anemia us when red blood cells break down (they can be misshapen, abnormal hemoglobin; most are circular looking, sickle cells can look like a crescent). Sickle cell is also autosomal recessive, meaning they receive two copies from the parent. Cystic fibrosis refers to damage done to the respiratory (lungs) and digestive system. They excessively secrete mucus leaving certain tissue vulnerable to infection.

It is also an autosomal recessive disorder. Tay Sachs destroys (demyelination) nerve cells in the spinal cord and brain. It is also autosomal recessive. Huntington’s disease is when nerve cells, over time, break down and can lead to early death. Huntington’s disease, conversely, is autosomal dominant; only one copy is needed for the disorder to develop. Discuss the inheritance of the ABO and Rh system human blood types. ABO blood group system, human blood, based on absence/presence of A/B antigens (surface of the red blood cell). The types are A, B, O, AB blood.

A & B alleles are codominant, so if both A and B are present they will be expressed together. O alleles have neither A or B antigens. O and O will result in O or O, an O or B will result in an O or B. A and A can result in A or O (same for B and O). AB and AB can result in A, B, or AB. They inherit it depending on the combo of their parent’s blood type. The Rh blood group is also a human blood system group. It is independently inherited from the ABO blood group alleles. Rh has Rh+ and Rh-. A + and + will result in a + or -, while a + and – will result in a + or -, but a – and – will result only in a -.

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