Gametogenesis

• Asexual production comes from 1 parent and is the reproduction of cells through either mitosis or binary fission. These cells can only vary with mutations, and otherwise, their identical genetics allow for them to thrive in a stable and predictable environment
• Sexual reproduction comes from 2 parents and is the production of sex cells through meiosis that has increasing variation in genetics through generations through the fusion of haploid sex cells from their parents. Due to this variation, they are able to survive in unpredictable and variable environments
• The sexual life cycle is the stages of life an organism undergoes (can be mitosis, binary fission, meiosis) beginning with a diploid zygote that develops into adult organism
• Meiosis is a process that reduces the number of chromosomes in their 4 daughter cells by half the amount in their starting parent cell to remain the correct number of chromosomes
• In fertilization two haploid cells (n=23) fuse to form 1 diploid (2n=46) zygote that unites two halves to reach full chromosome number- meaning the new cell has a unique combination of genes
• is 2n=46, where 2 is the ploidy representing the number of chromosomes in each cell
• Homologous chromosomes are the same size with the same genes in the same order with the same centromere location. In the case of mutation, there can be differences in the genes present in a specific locus causing the presence of alleles
• Gametogenesis is the process of forming egg and sperm cells
• Diploid cells include autosomal cells while haploid cells include sex cells
• As two parents with the same amount of genetic information combine, reductive division (meiosis) is required to keep a correct number of chromosomes within the body (diploid cells --> haploid cells)
• G1 occurs in interphase and is a metabolically active period in which the cell grows and prepares for DNA replication but the chromosomes are still loose
• the S phase occurs in the G1 phase of the cell cycle and is the time when DNA replication occurs at the two defined centrosomes
• In Prophase I, spindle fibers begin to form as DNA supercoils with homologous chromosomes pairing up (synapsis) so that they're aligned. They also use this closeness to "cross over" certain locus of their DNA for genetic variation
• Metaphase I is where the orientation of Homologous chromosomes are random and different- uninfluenced by each other- as they line up at the equator and spindle fibers complete their formation
• Anaphase I is where the chromosomes are separated (sister chromatids are still together) by microtubule and motor proteins who attach to the kinetochore at the centrosomes and move them to opposite poles of the cell
• Telophase I and Cytokinesis occur simultaneously and is where spindle fibers break and nuclei starts to form, allow DNA to uncoil and form chromatins that are part of two different daughter cells
• Prophase II is where DNA supercoils again and spindle fibers start to form and move to define poles and nuclear membrane starts to break down again
• Metaphase II is where the chromosome of each cell is lined up at the defined equator/metaphase plate
• Anaphase II is where the microtubules and microtubule motors separate sister chromatids and move them to opposite poles of the cell
• Telophase II is where spindle fibers begin to break down gain and nuclei starts to form, allowing DNA to uncoil from chromosomes (no longer X shaped, but single strand) to chromatins producing two haploid daughter cells each in Cytokinesis
• The M-phase includes Metaphase, Anaphase, and Telophase
• Supercoiling is the process by which DNA is tightly coiled into a compact form to prevent tangling or breaking of the strands during its moving during reproduction
• To form chromosomes, first eukaryote cell DNA wraps around histone proteins to form nucleosomes that are then coiled and stacked together to form chromatin fibers where, upon agreement with each other, form super-coiled chromosomes
• Chromatin fibers are the relaxed form of chromosomes that are loose and open, allowing for easy enzyme access
• Mitosis forms two identical diploid daughter cells from 1 division for cell replacement and tissue repairs
• Meiosis forms four unique daughter cells with half the DNA of its parents', used in the production of sex cells (sperm + egg)
• Mitotic spindles are made of hundreds of long fibers (microtubules) that are part of the cell's exoskeleton
• Kineticores in cells attach to spindle fibers and, with the help of motor proteins which progressively cut the fibers, moves the chromosomes/sister chromatids apart. They face opposite directions for each sister chromatid to allow separation when needed
• In an analogy, the chromosomes is a person hiking, its harness is the kineticore, tied around the person's waist (the centrosome) where the person is connected to the rope representing the microtubules in the cell, allowing for safe movement.
• Unreplicated chromatins are found in the G1 phase of Interphase as nucleosomes
• Replicated chromatins are found in the G2 phase of Interphase as sister chromatids
• Replicated chromosomes are found in Metaphase as super-coiled chromatids (chromosomes)
• Unreplicated chromosomes are found in Anaphase as single supercoiled chromosomes (sister chromatids that are apart)
• G2 is in Interphase and is a phase in which the cell continues to grow and synthesize proteins and organelles to prepare for meiosis.
• Sperm (male gamete) is mobile, with a small and long shape, and enough food reserves to sustain itself and no more. It is produced in large number and often.
• Egg (female gamete) is immobile, with a large, spherical shape that stores enough materials and nutritional reserves to sustain the embryo's initial development without additional production. 1 or 2 is made per month
• Variation allows for better survivability oftentimes and makes offspring that are more likely to reproduce and pass on their beneficial variation
• Variation within species = "Intra-species variation" = a defining part of life
• Independent assortment = when the orientation of one chromosome is uninfluenced by its homologous pair
• Meiosis creates variation through "crossing over" between sister chromatids of homologous chromosomes to create new combinations of alleles