Mitosis and Meiosis Quiz

Mitosis and Meiosis

• Mitosis is cell division that results in two identical daughter cells.
• It's used for tissue renewal, growth and development, and asexual reproduction.
• Cells in interphase (not dividing) have chromatin (euchromatin and heterochromatin) in long, thin fibres.
• Chromatin condenses to form chromosomes when a cell is ready to divide.
• A human cell has 46 chromosomes (23 pairs), homologous chromosomes having the same gene at the same loci but different alleles.
• A haploid cell has one set of 23 chromosomes (in sperm or egg).
• A diploid cell has two sets of 46 chromosomes.
• Autosomes are chromosomes 1-22, all homologous.
• Sex chromosomes are the 23rd pair (XX in females-homologous; XY in males—not homologous).
• Cell division in plants differs from animal cells in that they do not have centrioles. Instead, a cell plate forms in the centre of the cell.

Cell Cycle

• Interphase is the period when a cell is not dividing.
  • G1 phase: Growth, synthesizing new organelles
  • S phase: DNA replication (the cell makes a copy of each chromosome thus creates sister chromatids).
  • G2 phase: Second growth phase, cell increases in size, prepares for mitosis.
• During S phase, each chromosome consists of two identical sister chromatids.
• Sister chromatids are joined by a centromere.

Mitosis Stages

• Prophase: Chromatin condenses, nucleus remains intact but the nucleolus disappears, duplicated centrosomes separate and move to opposite poles, microtubule fibres extending between centrosomes form the mitotic spindle.
• Prometaphase: Nuclear membrane breaks down. Centrosomes at opposite ends of the cell. Some microtubules attach to kinetochores (structures on the centromere).
• Metaphase: Chromosomes align along the middle of the cell (metaphase plate). Sister chromatids are attached to microtubules coming from opposite poles.
• Anaphase: Centromeres break, sister chromatids separate, and the chromosomes are pulled to opposite poles of the cells by microtubules.
• Telophase: One copy of each chromosome is present at the opposite ends of the cell. Chromatin fibers start to loosen and become less coiled. Spindle fibers disappear. Nuclear membrane forms around chromosomes.
• Cytokinesis: Cytoplasm divides into two new daughter cells. Cell pinches in the middle (cleavage furrow in animal cells) or a cell plate forms in plant cells.

Meiosis

• Meiosis is cell division in sexually reproducing organisms, that produces cells with half the number of chromosomes as the parent cell for sexual reproduction in humans (sperm and eggs).
• Produces four genetically different haploid daughter cells.
• Has two rounds of division (meiosis I and meiosis II).
• In meiosis I, homologous chromosomes pair up and exchange genetic material in a process called crossing over.
• Homologous chromosome pairs separate at the end of Meiosis I.
• In meiosis II, sister chromatids separate.
• Meiosis increases genetic variation in offspring.

Genetic Variation

• Mutations are the original source of genetic variation.
• Reshuffling of alleles during sexual reproduction creates new combinations.
• Crossing over in meiosis increases variation.
• Independent assortment of chromosomes during meiosis affects variation.
• Random fertilization of gametes (sperm and egg) further increases variability.

Mendelian Genetics

• Genotype: Combination of alleles for a characteristic.
• Phenotype: Appearance of a characteristic
• Characters: Observable heritable feature.
• Traits: Variant of a character.
• Gene locus: Specific location of a gene on a chromosome.
• Inheritance: Transmission of traits from one generation to the next.
• Mendel's experiments: Show that traits are inherited in a distinct manner (law of segregation and independent assortment).
• Monohybrid cross: Observing the inheritance of a single trait.
• Dihybrid cross: Observing the inheritance of two traits.
• Law of segregation: Each individual has two alleles for each characteristic. During gamete formation, the alleles separate, so that each gamete receives only one allele for each characteristic.
• Law of independent assortment: Alleles of different genes separate independently during gamete formation.
• Dominant/recessive alleles: One allele can mask the expression of another

Speciation

• Species: Group of organisms that can interbreed and produce fertile offspring in nature
• Reproductive barriers: Prevent interbreeding between species.

• Prezygotic barriers: Prevent fertilization

• Postzygotic barriers: Prevent the resulting zygote from developing into a viable, fertile adult

• Allopatric speciation; populations geographically separated from one another.
• Sympatric speciation; populations in the same geographic area.

Phylogenetic History

• Phylogeny: The evolutionary history of a species or group of related species.
• Can represent relationships in a branching tree or diagram called a phylogenetic tree (cladogram)/phylogenetic tree.
• Similar characteristics (homologous) or traits are derived from a common ancestor.
• Similar adaptations (analogous) reflect adaptation to a similar environment.

Early Life on Earth

• Conditions on Earth early in its history allowed production of organic molecules from inorganic molecules, which may have occurred via extraterrestrial origin, abiotic synthesis, and Abiogenesis.
• The first cells were prokaryotes that dominated life until eukaryotes arose.
• Eukaryotes likely arose through endosymbiosis, in which one prokaryotic cell engulfed another.