Unit 6 HO Bio

Compare and contrast the parent-offspring relationship in asexual versus sexual reproduction

In asexual reproduction, offspring come from one parent and are genetically identical to that parent cell. In sexual reproduction, offspring come from two parents and inherit a unique combination of genes from both.

Analyze the evolutionary advantages and disadvantages of each reproductive strategy

For asexual reproduction the advantages are that it is quick and efficient and there is no mate needed. But, the disadvantages are that there is little genetic variation meaning that the adaptability of the species is low.

For sexual production the advantages are that the genetic variation is high meaning they can adapt well. The disadvantages are that its slower and it requires finding a mate.

Explain why cell division is essential for both prokaryotic and eukaryotic life

Prokaryotes: asexual reproduction

Unicellular eukaryotes: asexual reproduction

Multicellular eukaryotes: helps organism grow, repair, or maintain itself

Describe the process of binary fission in prokaryotes

In binary fission, the cell first replicates its DNA (genome). Next, DNA segregation occurs, where each copy of the genome moves to opposite sides of the cell. Finally, cytokinesis occurs, dividing the cytoplasm and cell membrane to produce two genetically identical daughter cells.

Explain the mechanism by which daughter chromosomes are separated during binary fission

After the DNA is replicated, each genome is moved to opposite sides of the cell membrane as the cell elongates. Once the chromosomes are separated, the cell membrane pinches inward and cytokinesis occurs.

Compare and contrast the structure of prokaryotic and eukaryotic chromosomes (circular vs. linear, histone proteins, chromatin organization)

Prokaryotic: A single circular DNA molecule, little protein association, located in the nucleoid region

Eukaryotic: Multiple linear DNA molecules, wrapped around histone proteins, found in a nucleus, organized as a chromatin

Describe the major phases: Interphase (G₁, S, G₂) and M phase (mitosis and cytokinesis). Explain the key events occurring during each stage. Understand the relative time spent in each phase.

Interphase is the longest phase of the cell cycle taking up at least 90% of the time. During Interphase G1, S, and G2 take place. G1 is the cell growing and continuing it's regular activity. The S phase is where the DNA (genome) is duplicated. The G2 phase is where the cell completes preparations for cell division. Next is the M phase which takes up around 10% of the whole cell cycle. First is mitosis which is split into 4 phases prophase, metaphase, anaphase, and telophase. In prophase, the nucleolus disappears, the chromatids turns into a chromosomes, and the spindle fibers appear. In metaphase the chromosomes align on the equator of the cell and the spindle fibers attach to them. In the anaphase the chromosomes are pulled apart to opposite poles by spindle fibers. In telophase the nucleolus appears, the chromosomes turn into chromatins, and the spindle fibers disappear. So, mitosis is the segregation of the DNA. Then cytokinesis occurs which is also part of the M phase. This is the division of the cytoplasm/splitting apart of the cell into two identical daughter cells.

G₁ Checkpoint (Restriction Point)

Assess cell size, nutrients, growth signals, and DNA integrity before committing to division

G₂ Checkpoint

Verify DNA replication is complete and check for DNA damage before entering mitosis

M Checkpoint (Spindle/Metaphase Checkpoint)

Ensure all chromosomes are properly attached to spindle fibers before proceeding to anaphase

Explain the role of cyclins and cyclin-dependent kinases (CDKs) in cell cycle regulation

CDK's are cyclin-dependent kinases which operate in conjunction with the changing concentration of the cyclins. CDK's phosphorylate molecules so that the molecules become reactive. Cyclins are proteins manufactured by the cell. As the concentration of the cyclin increases, the increased concentration causes the cell to move to the next phase of the cell cycle. The fluctuating cyclin concentration (increasing and decreasing) encourages the cell to move to the next phase of the cell cycle.

Describe how anchorage dependence, density-dependent inhibition, and chemical growth factors control cell division

Anchorage dependence is that cells must be in contact with a solid surface to divide. Density dependent inhibition is that cells stop dividing when they are crowded and touching surrounding cells. Chemical growth factors are proteins that cells need to divide. These all help control cell division to a good amount.

List and describe the events of each phase: prophase, metaphase, anaphase, and telophase

In prophase, the nucleolus disappears, the chromatids turns into a chromosomes, and the spindle fibers appear. In metaphase the chromosomes align on the equator of the cell and the spindle fibers attach to them. In the anaphase the chromosomes are pulled apart to opposite poles by spindle fibers. In telophase the nucleolus appears, the chromosomes turn into chromatins, and the spindle fibers disappear.

Explain the role of the mitotic spindle

Spindle fibers are protein fibers that attach to the centromere of each chromosome and then pull on the centromere until it splits and allows the chromatids to move away from each other during mitosis.

Compare cytokinesis in animal cells (cleavage furrow) versus plant cells (cell plate formation)

In animal cells, the cell membrane pinches inward to form a cleavage furrow. This pinching continues until the cell splits into two separate cells. In plant cells, the cell cannot pinch because of its rigid cell wall. Instead, a cell plate forms in the middle of the cell. The cell plate grows outward and becomes a new cell wall, separating the two new cells.

Describe the functions of mitosis: growth, tissue repair, asexual reproduction

Growth: Mitosis increases the number of cells in an organism. This is how multicellular organisms grow from a single fertilized egg into a fully developed organism. Instead of cells getting bigger and bigger, the body grows by making more cells through mitosis.

Tissue Repair: Mitosis replaces damaged or dead cells. For example, if you cut your skin, mitosis produces new skin cells to heal the wound. It also helps replace cells that naturally wear out, like skin cells and blood cells.

Asexual Reproduction: In some organisms (bacteria or yeast), mitosis allows reproduction without a partner. One organism can produce genetically identical offspring, since the new cells are clones of the original.

Explain how cancerous cells differ from healthy cells (loss of cell cycle control, anchorage independence, unlimited division potential)

Cancer cells ignore internal and external controls and experience uncontrollable cell division. The uncontrollable cell division crowds out normal cells and takes away nutrients from normal cells.

Describe the roles of proto-oncogenes and tumor suppressor genes (e.g., p53)

Proto oncogenes are genes that create proteins that regulate the cell cycle. Think of them as the "gas pedal" which control the rate at which the cell progresses through the cell cycle. Tumor suppressor genes code for proteins that regulate the cell cycle. These proteins perform tasks such as correcting DNA mutations, stopping or preventing cells from dividing and preventing a cluster of cells (tumor) from forming. Think of tumor suppressor genes as being the brake pedal.

Understand why cancer is typically not inherited (somatic vs. germline mutations)

Mutations in regular body cells (somatic) are not passed on to children because those cells are not used in reproduction. However, if a mutation happens in a gene that controls cell growth, it can cause cells to grow out of control and lead to Cancer. Mutations in sperm or egg cells (germline) can be passed on to children. If a sperm or egg with a mutation is involved in fertilization, the child will have that mutation in its DNA, which can increase the risk of Cancer.

Explain how chromosomes are paired (homologous chromosomes)

Every chromosome has a twin that resembles it in length, centromere position, and staining pattern

Distinguish between somatic cells and gametes

Somatic cells are typical body cells that are diploid and gametes are reproductive cells that are haploid

Distinguish between diploid (2n) and haploid (n) cells

Diploid is when the organism has two of each kind of chromosomes and a haploid is where the organism has one of each kind of chromosome

Explain why sexual reproduction requires meiosis (reduction of chromosome number)

Sexual reproduction is two gametes coming together. To maintain the same amount of chromosomes in this reproduction each gamete needs to go from diploid to haploid so that the zygote is diploid. Without meiosis, the chromosome would double each generation.

List and describe the phases of Meiosis I: prophase I (including crossing over and synapsis), metaphase I, anaphase I, telophase I

Meiosis I is where homologous chromosomes separate. In prophase I, homologous chromosomes pair up t and crossing over occurs. In metaphase I, homologous chromosome pairs line up at the middle of the cell randomly, causing independent assortment. In anaphase I, homologous chromosomes separate and move to opposite poles while sister chromatids remain attached. In telophase I, the cell divides, producing two haploid cells.

List and describe the phases of Meiosis II: prophase II, metaphase II, anaphase II, telophase II

Meiosis II is the division where sister chromatids separate. In prophase II, chromosomes condense and spindle fibers form. In metaphase II, chromosomes line up at the middle of the cell. In anaphase II, sister chromatids separate and move to opposite poles. In telophase II, nuclei reform and the cells divide, producing four genetically unique haploid cells.

Compare and contrast mitosis and meiosis (number of divisions, genetic outcome, chromosome number, function)

Mitosis has one division and creates 2 genetically identical daughter cells with the same number of chromosomes as the original cell. It is used for growth, tissue repair, and asexual reproduction. Meiosis has two divisions and creates 4 genetically different haploid gametes with half the number of chromosomes as the original cell. It is used for sexual reproduction.

Explain how genetic variation is produced through:

- Independent assortment of chromosomes

- Crossing over (recombination) during prophase I

- Random fertilization

Independent assortment occurs in metaphase I when homologous chromosome pairs line up randomly at the center of the cell, creating different combinations of chromosomes in gametes. Crossing over happens during prophase I when homologous chromosomes exchange segments of DNA, creating new combinations of genes. Random fertilization occurs when any sperm can fuse with any egg, producing a unique combination of genetic material in the offspring.

Calculate the number of possible chromosome combinations

2ⁿ where n = haploid number

Explain how and why karyotyping is performed

A karyotype is an ordered display of magnified images of an individuals chromosomes arranged in pairs. This is too look at the ploidy of an organism and look for any abnormalities.

Describe what information can be obtained from a karyotype

The ploidy and if there are any abnormalities

Define nondisjunction and explain when it occurs (meiosis I or II)

Nondisjunction is when the members of a chromosome pair fail to separate. It can happen in meiosis 1 or 11 but it is more detrimental in meiosis 1. If it happens in meiosis 1 then homologous chromosomes fail to separate there are zero gametes produced with the right amount of chromosomes but if it happens in meiosis 11 sister chromatids fail to separate and there are two gametes produced with the right amount of chromosomes.

Describe the consequences of nondisjunction

The consequence is aneuploidy which is when an organism has an incorrect number of chromosomes for their species.

Down syndrome

Trisomy 21 - an extra chromosome on the 21st pair

Explain how new species can form from errors in cell division (polyploidy, especially in plants)

The number of chromosomes defines each species. When you change the number of chromosomes, you can change the species. MOST eukaryotic organisms are diploid. Genetically engineered organisms can contain more than two copies of each chromosome and be polyploid. Most fruits and vegetables that are sold in stores have been genetically modified and can be polyploid, meaning they have more than two copies of each chromosome. Polyploidy leads to more favorable characteristics.