Bio 143 Cell Division: Mitosis & Meiosis

Mitosis:

(1) separates the genetic material duplicated during interphase into 2 identical sets of chromosomes and (2) reconstitutes a nucleus to house each set.

Suppose synapsis occurred between 2 homologous chromosomes and 1 had alleles for blue eyes & brown hair while the other had alleles for green eyes & blonde hair. How many different combos of these alleles is possible?

2⁴ or 16 combos

Synapsis occurs after chromosomal DNA has replicated. How many chromatids are involved in crossing over of a homologous pair of chromosomes?

4

If a nucleus has 8 chromosomes when it begins meiosis, how many chromosomes does it have after telophase I? Telophase II?

4 after telophase I; 2 after telophase II

How many chromosomes does it have after mitosis is complete?

8 because it's split into two.

What is a cell plate, and in what stage of mitosis of plants does it form?

A cell plate is a partition & occurs in telophase.

Haploid (n)

A nucleus with only 1 chromosome of each homologous pair.

Homologous pairs

A pair of chromosomes of the same type, one from each parent.

sister chromatids

A sister chromatid refers to either of the two identical copies (chromatids) formed by the replication of a single chromosome, with both copies joined together by a common centromere.

Alleles

Alleles are alternate states of a gene

Blastula

An early embryonic stage of a vertebrate & consists of a sphere of 25-100 cells with a high frequency of different mitotic stages.

How does cytokinesis differ in plant versus animal cells?

Animal cells form a cleavage furrow. Plant Cells have a cell plate.

Why is pinching of the cytoplasm inadequate for cytokinesis in plant cells?

Because they have a rigid cell wall.

Why would be choose an embryonic mass of cells for procedure 14.3 in which to study the stages of mitosis?

Because they undergo rapid cell division (whitefish).

Mitosis & Cytokinesis are often referred to collectively as "cellular division". Why are the more accurately called cellular replication?

Cells replicate the DNA

Interphase diagram

Chromosomes already replicated during interphase.

Telophase & cytokinesis

Chromosomes uncoil & nuclear membranes reform. Cleavage furrow separates the 2 cells.

Meristems

Contained in root tips; localized areas of rapid cell division due to active growth in the root tip.

Centrioles

Cylinders of microtubules found in centrosomes.

Cytokinesis

Divides the cell into 2 cells with identical genomes. May begin during Mitosis.

If a nucleus has 8 chromosomes during interphase, how many chromosomes does it have during metaphase?

Double to 16.

cell plate in plant cells

During cytokinesis, forms in the middle of the cell and grows out to the periphery. Will separate the 2 new cells.

Meiosis Diagram

Figure 15.1

Stages of mitosis in whitefish embryonic blastula.

Four stages

Gap 2

G2 Phase, molecules and structures necessary for mitosis are synthesized. Prepares the cell for mitosis.

Why would shuffling genetic material to produce new combos of characteristics be advantageous to a species?

Genetic variation

Interphase, Prophase & Prometaphase

Interphase not a part of nuclear replication but is essential to understanding it.

Mitosis

M phase; lasts for less than 10% of time of the cell cycle. Produces 2 identical nuclei from 1. Occurs in body cells in animals.

What are some minor difference and why are they minor?

Meiosis - 2 rounds of cell division; synapsis & crossing over in 4 daughter cells. Meiosis 4 daughter cells are not genetically identical.

Stages & Events fo Meiosis

Meiosis involves 2 divisions instead of one: The 2 reductions are called Meiosis I & Meiosis II

What are the major difference between the events of meiosis & mitosis?

Meiosis reduces chromosome numbers & has gametes (sex cells). Mitosis deals with body/somatic cells & they maintain the chromosome number

Centrosomes

Microtubule-organizing centers that contain cylinders of microtubules called centrioles.

When would it be deleterious (harmful)?

Mutations

Does the cell cycle have a beginning & and end?

No. It's continuous...an ongoing cycle.

Prometaphase Diagram

Nuclear membrane completely dissociated into vesicles & spindles fully formed. Sister chromatids attach to spindles via kinetochore microtubules.

Stages of Meiosis I

Prophase I Prometaphase I Metaphase I Anaphase I Telophase I & cytokinesis

Diploid

Refers to a nucleus with 2 of each type of chromosome.

Synthesis

S phase, a copy of the genome is synthesized. At the end of S phase, each chromosome consist of an identical pair of chromosomal DNA strands (sister chromatids) attached at a centromere.

Locate a plant cell in late telophase. What is the volume of the two new cells relative to the mature cell?

Similar volume because they are parent/daughter cells.

Metaphase Diagram

Sister chromatids align along the metaphase plate.

Prophase Diagram

Sister chromatids condense & spindles start to from. Nuclear membrane begins to dissociate into vesicles.

Anaphase Diagram

Sister chromatids get pulled apart.

Stages of Mitosis in plant Cells

Stages of mitosis in plant cells fig. 14.7

What stage of mitosis most often is associated with the beginning of cytokinesis?

Telophase (cytokinesis usually occurs after nuclear replication is complete).

Cell Cycle Figure 14.1

The cell cycle is depicted as a circle.

Crossing over

The exchange of genetic material among chromatids

Mitosis

The part of the cell cycle that includes the replication and division of the nucleus of a eukaryotic cell in preparation for cytokinesis.

Cytokinesis

The physical division of the cell & cytoplasm into halves that each contain a nucleus.

What region of a root has the most mitotic activity?

The root tip because it contains meristems.

polar fibers or polar microtubules

When the pairs of centrioles move apart and form an axis of proteinaceous microtubules.

Considering the surface to volume ratios of large versus small cells, is it adaptive for cells of a growing organism to remain small?

Yes, small cells require less energy.

mitotic spindle

a bridge of microtubules between the centrioles.

kinetochore

a complex of proteins that binds to the centromere.

Cellular replication

a major feature of the cell cycle; the end of the cell cycle.

Aster

an arrangement of microtubules radiating from a centriole.

Kinetochore Microtubules

anchored to proteins at the centromere.

Nuclei in sex cells are

diploid (2n); have 2 of each type chromosome.

Gap 1

first gap phase of interphase, G. Involves growth & preparation for DNA synthesis.

Cleavage furrow

formed during cytokinesis; begins on the periphery of the cell, pinches inward & divides the cytoplasm into two cells.

During meiosis, genetic material is replicated when?

genetic material is replicated once just before meiosis but divided twice during meiosis. Nuclei are haploid.

The difference between homologous chromosomes & sister chromatids:

homologous chromosomes are the maternal & paternal copies of the same chromosome. Sister chromatids are the two replicas of a single chromosome held together at there centrometers.

Meiosis reduces the number of chromosomes during two rounds of chromosome separation called______?

meiosis I & meiosis II

Interkinesis

period between meiosis I and meiosis II

Meiosis

process that produces haploid daughter nuclei & is sometimes called reduction division.

Stages of Meiosis II

prophase II, prometaphase II, metaphase II, anaphase II, telophase II & cytokinesis

5 stages of Mitosis

prophase, prometaphase, metaphase, anaphase, telophase

Gamate

sex cell; an egg or a sperm cell

The cell cycle (circle) begins with

the formation of a new cell and ends with the replication of that cell.

Synapsis

the pairing of homologous chromosomes during meiosis

Cell cycle

the repeating set of events in the life of a cell