Test 6 Review Sheet (Topics 14 - 17, 20f and Labs)

Topic 14 Part 1: Cell Cycle, Division & Mitosis

• Cells increase their numbers through cell division.
• Cells decrease their numbers through apoptosis (programmed cell death). Example: Cells infected with a virus may undergo apoptosis to prevent the spread of the infection.
• The beginning and end of one round of the cell cycle is marked by cell division.
• Interphase:
  • G1 (Gap 1): Cell grows and performs normal functions.
  • S (Synthesis): DNA replication occurs.
  • G2 (Gap 2): Cell prepares for division, synthesizes proteins and organelles.
• M Phase:
  • Mitosis: Nuclear division.
  • Cytokinesis: Cytoplasmic division.
• Prokaryotic cells favor binary fission, which is simpler and faster than eukaryotic cell division (mitosis and meiosis).
• Controlling the rate of cell cycle progression is crucial for proper development and to prevent diseases like cancer. Too slow: delayed growth or repair. Too quickly: uncontrolled cell growth (cancer).
• Checkpoints are control mechanisms that ensure the cell cycle proceeds correctly. They are important for detecting and correcting errors.
• Chemicals (e.g., cyclins and cyclin-dependent kinases (CDKs)) act as the "chemical clock" inside a cell and control its progression through the cell cycle.
• If a cell passes the G1 checkpoint and enters the S phase, it will likely undergo DNA replication and continue through the cell cycle to divide.
• If a cell does not pass the G1 checkpoint and is not going to divide, it enters the G0 phase (a resting state).
• Examples of cells that frequently divide: skin cells, cells lining the digestive tract. Cells that seldom/never divide: nerve cells, muscle cells. Cells that only divide when needed: liver cells (to repair damage).

Part 2: Chromosomes

• Relationship: Linear DNA makes up genes. Genes are arranged on chromosomes. Chromosomes are made of chromatin (DNA and proteins). Visible chromosomes are condensed chromatin seen during cell division. A genome is the complete set of genetic material in an organism.
• An unduplicated chromosome is a single DNA molecule. A duplicated chromosome consists of two identical sister chromatids joined at the centromere.
• Chromosomes are duplicated during the S phase of the cell cycle and are unduplicated after cell division (cytokinesis).
• A duplicated chromosome consists of two sister chromatids, which are generally considered to be identical to one another immediately after DNA replication. However, some differences can arise due to mutations or errors during replication.
• Homologous pairs are two chromosomes that carry the same genes but may have different alleles (versions of those genes). They are the same size and shape.
• Autosomes are non-sex chromosomes. In a diploid cell, they exist in homologous pairs.
• Sex chromosomes determine the sex of an organism. Females have two X chromosomes (XX), and males have one X and one Y chromosome (XY). The X and Y chromosomes are not entirely homologous.
• The male parent determines the sex of their children because they can contribute either an X or a Y chromosome, while the female parent always contributes an X chromosome.
• Diploid refers to cells with two sets of chromosomes (2n). Haploid refers to cells with one set of chromosomes (n). Human somatic (body) cells are diploid. Human gametes (sperm and egg) are haploid.

Part 3: Cell Division

• Asexual reproduction involves a single parent and produces offspring that are genetically identical to the parent. Examples: binary fission in bacteria, budding in yeast, vegetative propagation in plants.
• The offspring of asexual reproduction are genetically identical (clones) to the parent, barring any mutations.
• Mitosis is the division of the nucleus. Cytokinesis is the division of the cytoplasm.
• The point of mitosis is to produce two daughter cells with the same number of chromosomes as the parent cell. This is important for growth, repair, and asexual reproduction.
• Sister chromatids are separated during mitosis.
• 5 Phases of Mitosis:
  1. Prophase: Chromosomes condense, nuclear envelope breaks down, spindle fibers form.
  2. Prometaphase: Spindle fibers attach to centromeres.
  3. Metaphase: Chromosomes align at the metaphase plate.
  4. Anaphase: Sister chromatids separate and move to opposite poles.
  5. Telophase: Chromosomes decondense, nuclear envelope reforms, cytokinesis begins.
• Cytokinesis in cells with walls (plant cells) involves the formation of a cell plate that becomes the new cell wall. In cells without walls (animal cells), cytokinesis occurs through the formation of a cleavage furrow.
• Karyotypes can be analyzed to determine the number and structure of chromosomes. Duplicated chromosomes are seen in cells undergoing division (prophase, metaphase). Unduplicated chromosomes are seen in cells in interphase or after cytokinesis. Homologous chromosomes are present in diploid cells. Non-homologous chromosomes are chromosomes that do not carry the same genes. These scenarios represent different stages of the cell cycle.

Topic 15: Meiosis

• Sexual reproduction involves the fusion of gametes (sperm and egg) from two parents to produce offspring with a combination of genetic material from both parents.
• The sexual reproduction life cycle includes:
  • Mitosis: Occurs in both diploid and haploid phases for growth and development.
  • Meiosis: Reduces chromosome number from diploid to haploid to produce gametes.
  • Diploid Phase: The zygote and somatic cells are diploid.
  • Haploid Phase: Gametes are haploid.
  • Gametes: Sperm and egg cells.
  • Zygote: A diploid cell resulting from the fusion of two haploid gametes.
• Mitosis vs. Meiosis:
  • Purpose: Mitosis for growth, repair, asexual reproduction. Meiosis for sexual reproduction, producing genetically diverse gametes.
  • Number of parent cells: Mitosis - 1. Meiosis - 1.
  • Number of chromosomes in the parent cell: Mitosis - diploid or haploid. Meiosis - diploid.
  • Parent cell diploid or haploid: Mitosis - both. Meiosis - diploid.
  • Number of divisions involved: Mitosis - 1. Meiosis - 2 (Meiosis I and Meiosis II).
  • DNA separated: Mitosis - sister chromatids. Meiosis - homologous chromosomes in Meiosis I, sister chromatids in Meiosis II.
  • Number of daughter cells produced: Mitosis - 2. Meiosis - 4.
  • Chromosome number of daughter cells: Mitosis - same as parent (diploid or haploid). Meiosis - half of parent (haploid).
  • Daughter cells diploid or haploid: Mitosis - same as parent. Meiosis - haploid.
• The point of meiosis is to produce haploid gametes with genetic variation.
• Meiosis involves two divisions: Meiosis I (homologous chromosomes separated) and Meiosis II (sister chromatids separated).
• Crossing over (exchange of genetic material between homologous chromosomes) and independent assortment (random alignment of chromosomes during metaphase I) contribute to the genetic uniqueness of daughter cells produced by meiosis.
• Crossing over occurs during prophase I of meiosis. The exact timing is during the pachytene stage of prophase I.
• Two reasons meiosis is biologically important:
  1. Reduces chromosome number to produce haploid gametes for sexual reproduction.
  2. Introduces genetic variation through crossing over and independent assortment.
• Major events in meiosis: Similar to mitosis, but with two rounds of division. Key differences in Prophase I (crossing over) and Metaphase I (independent assortment).
• Be able to identify stages of mitosis and meiosis from diagrams based on chromosome behavior (e.g., presence of sister chromatids, homologous chromosomes pairing, alignment at metaphase plate).

Topic 16: Genetics Part 1: Mendelian Genetics

• Inheritance is the passing of traits from parents to offspring. Studying inheritance allows us to make predictions about the traits of future generations.
• Gregor Mendel was an Austrian monk who is considered the father of modern genetics. He discovered the basic principles of inheritance by experimenting with pea plants.
• Definitions:
  • Alleles: Different versions of a gene.
  • Homozygous: Having two identical alleles for a gene.
  • Heterozygous: Having two different alleles for a gene.
  • Dominant: An allele that masks the expression of another allele.
  • Recessive: An allele whose expression is masked by a dominant allele.
• Genotype is the genetic makeup of an individual (e.g., BB, Bb, bb). Phenotype is the observable characteristics of an individual (e.g., brown eyes, blue eyes).
• Eye color example:
  • Homozygous dominant (BB): Brown eyes
  • Heterozygous (Bb): Brown eyes
  • Homozygous recessive (bb): Blue eyes
• New alleles arise through mutations in DNA.
• Dominant alleles do not tend to skip generations because they are expressed even when only one copy is present.
• Polydactyly is having extra digits (fingers or toes). Progeria is a rare genetic condition causing premature aging. Polydactyly can be easily passed through generations if it does not affect survival. Progeria typically results from a new germ-line mutation, making it less likely to be inherited.
• Recessive alleles tend to skip generations because they are only expressed when two copies are present (homozygous recessive). Heterozygous individuals are carriers, meaning they have the allele but do not express the trait.
• A carrier is an individual who is heterozygous for a recessive allele and can pass the allele to their offspring without expressing the trait themselves.
• Albinism is a recessive genetic condition characterized by a lack of pigment in the skin, hair, and eyes. Individuals with albinism are homozygous recessive for the albinism allele.

Part 2: Exceptions to Mendelian Genetics

• Mendel was "lucky" because the pea plant characteristics he studied were controlled by single genes with two alleles that exhibited simple dominant-recessive inheritance.
• Incomplete dominance is a pattern of inheritance in which the heterozygous phenotype is intermediate between the two homozygous phenotypes. Example: Snapdragons, where a red-flowered plant (RR) crossed with a white-flowered plant (WW) produces pink-flowered plants (RW).
• In incomplete dominance, there are three phenotypes (red, white, pink) compared to two in a dominant-recessive pattern.
• Achondroplasia is a form of dwarfism. Individuals with achondroplasia can be homozygous dominant (severely affected and usually lethal), heterozygous (affected with dwarfism), or homozygous recessive (normal height). This represents an incompletely-dominant pattern because the heterozygous phenotype is less severe than the homozygous dominant phenotype.
• Sickle-cell anemia is a genetic disorder in which red blood cells are abnormally shaped. Heterozygous individuals (carriers) have some resistance to malaria, which is why the sickle-cell allele is still found in a fairly high percentage of populations that live near the equator.
• Codominance is a pattern of inheritance in which both alleles are expressed equally in the heterozygous phenotype. Example: Human blood types (AB blood type, where both A and B antigens are expressed).
• Not all genes only have 2 alleles. Multiple alleles can affect the patterns of inheritance and result in more phenotypes.
• Polygenic inheritance is a pattern of inheritance in which a trait is controlled by multiple genes. Human skin color is an example of this, as it is determined by several genes.
• Pleiotropy is when a single gene affects multiple traits. Example: In cats, a gene affecting coat color can also affect eye color and other physical characteristics.
• The environment can influence gene expression. Example: In Siamese cats and Himalayan rabbits, the enzyme responsible for pigment production is temperature- sensitive, resulting in darker fur in cooler areas of the body.
• Genetics Prediction Problems: Be able to complete Punnett Squares for Monohybrid crosses, Dihybrid crosses, Incomplete dominance and codominance, Multiple alleles (especially human blood types), Sex linkage and Pedigree charts.

Topic 17: Chromosomal Inheritance

• Mendel's Law of Independent Assortment states that genes for different traits are inherited independently of one another. Mendel's Law of Segregation states that each individual has two alleles for each trait, and these alleles separate during gamete formation.
• Linkage refers to genes located close together on the same chromosome being inherited together.
• The degree of linkage is higher if the genes are located on the same chromosome and close together. It is lower if the genes are located on different chromosomes or far apart from one another on the same chromosome (due to potential crossing over).
• Sex linkage refers to genes located on the sex chromosomes (X or Y).
• A gene must be located on a sex chromosome (X or Y) to be considered sex-linked.
• The location of a gene on a sex chromosome changes its pattern of inheritance. In males, who have only one X chromosome, a recessive allele on the X chromosome will always be expressed. In females, who have two X chromosomes, a recessive allele on the X chromosome will only be expressed if she is homozygous recessive.
• Red-green colorblindness and hemophilia are sex-linked conditions (more specifically, X-linked recessive). These conditions are more common in males because they only have one X chromosome, so they only need to inherit one copy of the recessive allele to be affected.
• X-chromosome inactivation is a process in which one of the two X chromosomes in female mammals is randomly inactivated. This helps females "cope" with the presence of two X chromosomes by preventing them from expressing twice as many X-linked genes as males. Barr bodies are the inactive X chromosomes.
• Calico cats represent a visual example of X-chromosome inactivation. The different colors of fur (e.g., orange and black) are due to different X-linked alleles being expressed in different cells.
• Nondisjunction is the failure of chromosomes or sister chromatids to separate properly during meiosis. Monosomy is when a cell has only one copy of a chromosome. Trisomy is when a cell has three copies of a chromosome.
• Mistakes in meiosis I (homologous chromosomes fail to separate) and meiosis II (sister chromatids fail to separate) can result in nondisjunction.
• Trisomy 21 is Down syndrome, which is caused by having three copies of chromosome 21.
• Nondisjunction can result in an abnormal number of sex chromosomes (e.g., XXY, XYY, XXX, XO).
• Be able to identify a chromosomal disorder based on a karyotype by looking for extra or missing chromosomes or structural abnormalities.

Topic 20f: Immune System, Vaccines and COVID

• The innate (primary) immune system is the first line of defense against pathogens. It includes physical barriers (e.g., skin, mucous membranes), chemical barriers (e.g., stomach acid), and cellular defenses (e.g., macrophages, neutrophils).
• Antibodies are proteins produced by B cells (plasma cells) that bind to specific antigens (molecules on pathogens). This interaction helps to neutralize the pathogen and mark it for destruction by other immune cells.
• Vaccines contain weakened or inactive pathogens, or parts of pathogens (e.g., antigens or mRNA), that stimulate an immune response without causing disease.
• The body reacts to vaccines by producing antibodies and memory cells that provide long-lasting protection against the targeted disease.
• COVID-19 primarily targets the respiratory system, leading to symptoms such as cough, fever, and shortness of breath. The virus can also affect other organs, such as the heart, brain, and kidneys.
• mRNA vaccines contain messenger RNA that codes for a viral protein (e.g., the spike protein of SARS-CoV-2). The mRNA is delivered into cells, where it is translated into the viral protein, triggering an immune response.
• The rapid antibody test for COVID works by using labeled primary antibodies to bind to viral antigens, unlabeled primary antibodies, and secondary antibodies labeled with enzymes for detection.

Achieve Mitosis Lab

• Recognize phases of the cell cycle (interphase, prophase, metaphase, anaphase, telophase/cytokinesis) from images based on chromosome appearance and location.
• Determine whether an image of a cell represents an animal or a plant source based on the presence or absence of a cell wall and the mechanism of cytokinesis.
• Determine which phase of mitosis is typically the shortest (metaphase) and which is the longest (prophase) in onion cells.

Achieve Genetics of Corn Lab

• Mendel's Law of Segregation tells us that alleles for each trait separate during gamete formation, so each gamete carries only one allele for each trait.
• Mendel's Law of Independent Assortment tells us that alleles for different traits are inherited independently of one another.
• The purpose of the Chi-Square Goodness of Fit Test is to determine whether the observed results of a genetic cross are consistent with the expected results based on Mendelian inheritance.
• A p value of less than 0.05 indicates that the observed results are significantly different from the expected results, suggesting that the null hypothesis (that the observed results fit the expected results) should be rejected. A p value greater than 0.05 indicates that the observed results are not significantly different from the expected results, suggesting that the null hypothesis should not be rejected.
• Calculate the probability that a particular genotype or phenotype results from a genetic cross using Punnett Squares (monohybrid and dihybrid).