Interphase:
-the cell replicates its chromosomes
-each chromosome has two sister chromatids held together by a centromere
Prophase 1 chromosomes coil up and a spindle forms
-homologous chromosomes come together matched gene by gene forming a tetrad
-Crossing Over may occur when chromatids exchange genetic material
-this occurs two or three times per pair of homologous chromosomes
-Crossing Over results in new combinations of alleles on a chromosomes
Metaphase 1:
-the centromere of each chromosome becomes attached to a spindle fiber
-the spindle fibers pull the tetrads to the equator of the spindle
-homologous chromosomes are lined up side by side as tetrads
Anaphase 1:
-homologous chromosomes separate and move to opposite ends of the cell
-centromeres do not split
-this ensures that each new cell will receive only one chromosome from each homologous
pair
Telophase 1:
-the spindle breaks down and the chromosomes uncoil
-the cytoplasm divides to yield two new cells
-each cell has half the genetic information of the original cell because it has only one homologous
chromosome from each pair
Prophase II-
-a spindle forms in each of the two new cells and the fibers attach to the chromosomes
Metaphase II-
-the chromosomes are pulled to the center of the cell and line up randomly at the equator
Anaphase II-
-the centromere of each chromosome splits the sister chromatids separate and move to opposite poles
Telophase II nuclei re form the spindles break down the cytoplasm divides identical to mitosis (Meiosis II)
What Meiosis produces four haploid sex cells from one original diploid cell each haploid cell contains one chromosome from each homologous pair haploid cells will become gametes transmitting genes to offspring
I hope this helps
Answer:
- A signal for apoptosis that comes from outside the cell is when a cell detaches from extracellular matrix. If this happens, a transmembrane signal is triggered.
- Two examples of cellular occurrences that would prompt an apoptosis signal from inside the cell are:
1. Damaged DNA
2. Increase of cytosolic calcium concentration
Explanation:
Apoptosis can be activated from an intrinsic or an extrinsic pathway. The intrinsic pathway is activated when a cell senses stress (for example, damaged DNA or high cytosolic calcium concentration) and triggers death proteins to activate apoptosis mechanism inside of it; the extrinsic pathway refers to the apoptosis triggered by signals that come from other cells. In this scenario, ligands bind to cell-surface death receptors and activates a death-inducing signal.
Kidney preserve or excrete H⁺ ion and HCO₃⁻ ion to regulate the blood pH.