MICROSCOPIC EXAMINATIONS OF THE DIVIDING CELLS Flashcards
The chromosomes shorten, thicken and become visible as thick rods. They are longitudinally double, with each half called a chromatid. The chromatids are closely pressed against each other throughout their length. Nucleoli and the nuclear membrane completely disappear by late prophase. Spindle fibers would then radiate from microtubule organizing centers.
Prophase
The chromosomes, which are maximally condensed, align at the equatorial plane. The chromatids in each chromosome separate from each other except at the centromere. The spindle fibers attach to the kinetochore proteins on opposite sides of the centromere.
Metaphase
Each chromatid of a chromosome possesses its own centromere. Prior to anaphase, the centromeres of sister chromatids function as one. At anaphase, the centromeres become functionally double. Each member of the doubled chromosome begins to move toward opposite poles. The poleward movement of the chromosomes is due to depolymerization of the spindle fibers attached to the kinetochores at the centromere.
Anaphase
Upon reaching the opposite poles, the chromosomes regroup into two nuclear regions. They begin to uncoil and lengthen, and finally lose their visible identity. Cytokinesis usually follows. In plant cells, the cytoplasm is divided via cell wall plate formation where separation starts from the inside towards the periphery. In animal cells, cytokinesis occurs via cleavage furrow formation that starts from the periphery going inwards.
Telophase
Objectives of Lab Act 3
- Illustrate the chromosomal behavior which occur in somatic and sex cells during mitosis and meiosis;
- Identify the specific events in mitosis and meiosis that allow the inheritance of traits and generation of genetic variation.
Mitosis in multicellular organisms and unicellular organisms
multicellular organisms = increasing the number of cells and of replacing worn out tissues
unicellular organisms = mode of reproduction
Why is there a need to change the water daily?
Oxygen Supply
Nutrient and Waste Balance
Preventing Microbial Growth
What time is the mitotic activity optimal
between 11 am to 2 pm
Why do we need to put the root tip in Farmer’s fluid?
Fixing
Prevention of decay
Soften tissue
Why do we need to put the onion root tip in 1 N HCL for 10 minutes?
To hydrolyze to soften the tissues and make them transparent
Why use acetocarmine stain on the root tip?
Contrast = DNA-specific stain
Chromosome number of onion
2n=16
Chromosome number of whitefish (coregonus sp.)
2n = 80
At what stage of mitosis is it easiest to determine the kind and number of chromosomes? Why?
Metaphase = chromosomes are fully condensed and line up in the middle
which of the stage of mitosis appears to be the most numerous? Why do you think so?
Prophase = prophase lasts longer, as it involves the condensation of chromosomes, formation of spindle fibers, and disintegration of the nuclear envelope
