LECTURE 2: THE CHROMOSOMAL BASIS OF HEREDITY

Mitosis

Occurs in somatic and germ/sex cells

Mitosis

Mitosis

Mitosis

Mitosis

Mitosis

Normally, no crossovers

Mitosis

Mitosis

Relevance of this _______ in genetics:

Parental and daughter nuclei have identical genetic and chromosome content. Therefore, genes can arise only from pre-existing genes.

Mitosis

Relevance of this _______ in genetics:

Chromosomes retain the same properties/shape, therefor integrity of genes is retained as well.

Mitosis

Relevance of this _______ in genetics:

Mutations can be retained and perpetuated, cell generation after cell generation.

Mitosis

Relevance of this _______ in genetics:

_________ assures continuity and constancy of genetic makeup of cells, tissues, and organs.

Meiosis

Occurs in cells in the sexual cycle (sex cells: egg and sperm, spore)

Meiosis

Meiosis

Meiosis

Meiosis

Meiosis

Meiosis

Meiosis

Relevance of this _______ in genetics:

Conservation of chromosome number of species generation after generation.

Meiosis

Relevance of this _______ in genetics:

Combination and recombination of maternal and paternal chromosome.

Meiosis

Relevance of this _______ in genetics:

Provides the physical basis for segregation of pared genes (Each of the alleles end up in different gametes).

Meiosis

Relevance of this _______ in genetics:

Crossing-over at pachytene results to new genetic combination and recombination or genetic variability.

A nucleosome is the basic repeating subunit of chromatin packaged inside the cell's nucleus.

It is made up of a coil of DNA wound around a histone core. The core has eight histone molecules namely (two of each): H2A, H2B, H3, and H4 histones.

What are nucleosomes?

Chromatin fibers which are made of nucleosomes, consisting of a DNA coil wound around a histone core.

What are chromosomes made up of?

telomere

This part of the chromosome:

Is a determinant of your lifespan

• When this part is short, you are now much more prone to diseases

telomere

This part of the chromosome:

Does not contain active genes, only a protein cap for the ends of the chromosomes

telomere

This part of the chromosome:

The tips of chromosome arms are called _____________; these provide stability to the chromosome.

Kinetochores

This part of the chromosome:

___________ are the site of attachment of spindle fibers.

Centromere or Primary Constriction

This part of the chromosome:

Location in which spindles are attached to, and force is applied for separation during anaphase

Centromere or Primary Constriction

This part of the chromosome:

Also, where kinetochore proteins can be found, which are what the spindle fibers are bound to and the depolymerization of the spindle fibers enables the chromosome to move to the opposite poles.

• metacentric, when the centromere is located at the middle

• submetacentric, when the centromere is close to the middle

• acrocentric, when the centromere is located near one end

• telocentric, when the centromere is at the end of the chromosome

Differentiate between the different positions of the centromere along the length of the chromosome which contributes to the shape of the chromosome during cell division:

• metacentric

• submetacentric

• acrocentric

• telocentric

Secondary Constriction

This part of the chromosome:

Constrictions apart from the centromere which form the satellite.

Secondary Constriction

This part of the chromosome:

This is often associated with regions where the nucleolus is formed or attached.

Nucleolus-Organizing region

This part of the chromosome:

These are chromosomal regions crucial for the formation of the nucleolus

Nucleolus-Organizing region

This part of the chromosome:

When a nucleolus is visible, it can be seen to be attached to the nucleolus.

nucleolus organizer

The chromosome where the Nucleolus-Organizing region is located is known as the _____________-.

chromomeres; knobs

When a mitotic chromosome is stretched out, it would be observed to consist of a string of characteristic particles of unequal sizes at unequal distances apart. The smaller “beads on the string” are called _____________; the larger ones are called _____________.

Knobs

This part of the chromosome:

__________ are well defined cytological markers consisting of large chromomeres

Genome

This has a complete set of genes or chromosomes coming from a male/female parent cell

Mitosis

It is considered an equational division

Mitosis

Results in 2 identical cells

Meiosis I

It is also considered a reductional division

Meiosis

Results in haploid cells that are distinct

G-1 Phase

During this phase:

It is the first gap period and the longest phase in the cell cycle.

G-1 Phase

During this phase:

During this phase, the cell increases in volume by imbibing water and nutrients and building new protoplasm and cytoplasmic organelles, such as the ER, Golgi apparatus, ribosomes, mitochondria, and chloroplasts.

G-1 Phase

During this phase:

In addition to the cytoplasmic organelles, secretion granules, storage granules and cell wall materials are also elaborated in this phase.

G-1 Phase

During this phase:

Strictly speaking, therefore, this phase is only a gap in the reproductive life of the cell.

S Phase

During this phase:

During this period DNA replication or synthesis is the most important activity in the cell.

S Phase

During this phase:

Duplication of centrosomes occur.

G-2 Phase

During this phase:

Further growth, production of proteins, organelles, and other molecules.

G-2 Phase

During this phase:

Characterized by the synthesis of RNA and proteins necessary for chromosome synthesis and for the mitotic spindle.

G-2 Phase

During this phase:

This period is generally shorter than the G-1 and S phases.

M Phase

During this phase:

During this period structural changes of chromosomes are visible.

The M phase may be subdivided into four stages, namely:

• prophase

• metaphase

• anaphase

• telophase

The M phase may be subdivided into four stages, namely:

• ___________

• ___________

• ___________

• ___________

Prophase

During this phase of mitosis:

This stage is characterized by the appearance of cold, contracted threads - the chromosomes.

Prophase

During this phase of mitosis:

Chromosomes shorten and thicken, and the nucleolus diminishes in size.

Prophase

During this phase of mitosis:

In some cells, the centrosome divides into two portions, each containing a centriole. One migrates along the nuclear membrane until it is opposite the other.

Metaphase

During this phase of mitosis:

The nuclear membrane disappears, and the spindle fibers soon appear.

Metaphase

During this phase of mitosis:

The chromosomes, which are maximally condensed, and the chromatids in each chromosome, which separate from each other except at the centromeres, align at the equatorial plate.

Metaphase

During this phase of mitosis:

The spindle fibers are attached on the opposite sides of the centromere.

Anaphase

During this phase of mitosis:

The centromeres become functionally double at _____________ and the chromatids begin to move toward the opposite poles.

Anaphase

During this phase of mitosis:

The chromatids first separate the centromere, and the arms are passively dragged along.

Anaphase

During this phase of mitosis:

The poleward movement of the chromosomes is due to the depolymerization of spindle fibers attached to the kinetochore.

Telophase

During this phase of mitosis:

Upon reaching the opposite poles, the chromosomes regroup into two nuclear structures at this phase.

Telophase

During this phase of mitosis:

In each nucleus the chromonemas unwind, the chromosomal proteins disperse, thus losing their stainability.

Telophase

During this phase of mitosis:

At the same time, the nucleolar organizers are activated to synthesize new nucleolar materials.

phragmoplast; cell plate

During this Cytokinesis of Plant cells:

In plant cells, Cytokinesis is accomplished by the formation of a cell plate. As the chromosomes separate during anaphase, the cytoplasm divides and the cytoplasmic contents are distributed. At the same time the _____________ is formed at the metaphase plate. It increases in diameter as cytokinesis continues until it reaches the lateral walls. A thin membrane forms across the center opening of it and eventually cuts the cell into two. This membrane is the __________, the primordium of a new cell wall.

furrowing

During this Cytokinesis of Animal cells:

In animal cells, cytokinesis proceeds by _________. It originates as an indentation of the outer membrane at the position of the metaphase plate. This indentation gradually moves inward and halves the cell into two daughter cells.

Prophase I - consists of 5 substages which are?

Leptotene

During this stage of Prophase I:

thin thread stage

Leptotene

During this stage of Prophase I:

Replicated chromosomes begin to condense

Zygotene

During this stage of Prophase I:

A bivalent consisting of a pair of homologous chromosomes begins to form.

Zygotene

During this stage of Prophase I:

Synapsis begins as a synaptonemal complex is forming, which is required for recombination.

Pachytene

During this stage of Prophase I:

During this stage, chromatid breaks occur and are repaired.

Pachytene

During this stage of Prophase I:

The subsequent repairs cause crossing-over between homologues, leading to the formation of the chiasma at the point of exchange.

Diplotene

During this stage of Prophase I:

• Chiasma is formed.

• Synaptonemal complex begins to dissociate.

Diplotene

During this stage of Prophase I:

The longitudinal separation of the bivalent initiates diplonema wherein the homologues are separated except at the chiasmata.

Diplotene

During this stage of Prophase I:

The chromosomes are actively shortening, and their coiled nature is very apparent.

Diplotene

During this stage of Prophase I:

Later, the chiasmata appear to move toward the end of the chromosome, in the process known as terminalization.

Diakinesis

During this stage of Prophase I:

The chromosomes become more contracted and assume unique configurations due to the repulsion of the chromatid pairs.

Diakinesis

During this stage of Prophase I:

• The nucleolus dissociates, and spindle formation begins.

• The bivalents are distributed evenly in the nucleus.

Metaphase I

During this phase of meiosis:

The nuclear membrane disintegrates, and spindles appear.

Metaphase I

During this phase of meiosis:

Alignment of bivalents at the equatorial plane

Anaphase I

During this phase of meiosis:

Bivalent separates into univalent chromosomes, which are unpaired with only two sister chromatids

Anaphase I

During this phase of meiosis:

Each ________________ group is composed of a haploid number of chromosomes, which therefore means this process accounts for the reductional phase of Meiosis

Telophase I

During this phase of meiosis:

• Chromosome coils begin to relax.

• Cytoplasm is divided, and in some species, the nuclear membrane is formed.

Telophase I

During this phase of meiosis:

A brief transitional stage called interkinesis occurs before the cell process to the next stage.

Cytokinesis

During this phase of meiosis:

Separation of the cells through the formation of the cleavage furrow.

Meiosis I is reductional division because each daughter nucleus contains only half the chromosome number of the parental cell.

Meiosis I is reductional division why?

False

In Meiosis, each daughter cell has a different genetic composition due to differences between paternal and maternal chromosomes and recombination brought by crossing-over during chiasmata formation.

In Meiosis each daughter cell has a similar genetic composition due to similarities between paternal and maternal chromosomes and recombination brought by crossing-over during furrow formation.

T or F?

The General Pattern of Eukaryotic Life Cycles include the following:

1. The diploid phase, characterized by a series of mitotic divisions

2. Meiosis, the first step in gamete formation

3. Series of haploid mitotic divisions

4. Fertilization or fusion of two gametes or haploid nuclei, thus restoring the diploid phase.

The General Pattern of Eukaryotic Life Cycles include the following:

1. __________________

2. __________________

3. __________________

4. __________________
   

Hint:

Terminal or gametic meiosis

What type of Life Cycle is this describing:

Found in animals, including humans, and some lower plants.

Terminal or gametic meiosis

What type of Life Cycle is this describing:

In males, spermatogonia gives rise to primary spermatocytes and, through meiosis, produces four spermatids, which are differentiated into spermatozoa, each with a haploid chromosome number.

Terminal or gametic meiosis

What type of Life Cycle is this describing:

In females, oogonia give rise to primary oocytes and secondary oocytes and, through meiosis, produces four haploid daughter nuclei, three of which become infertile polar bodies, and one becomes the mature ovum (22 + X).

Terminal or gametic meiosis

What type of Life Cycle is this describing:

The ovum may be fertilized by an X-carrying sperm cell (22 + X) to produce a female (44 + XX) progeny or by a Y-carrying sperm cell (22 + Y) to produce a male (44 + XY) progeny.

Terminal or gametic meiosis

What type of Life Cycle is this describing:

Terminal or gametic meiosis

What type of Life Cycle is this describing:

aka diploid-dominant life cycle

Terminal or gametic meiosis

What type of Life Cycle is this describing:

Its name refers to the fact that gametes are the result of meiosis

During this life cycle a reproductive cell produces haploid gametes (sex cells such as egg and sperm) that combine to produce a zygote

Intermediary or sporic meiosis

What type of Life Cycle is this describing:

Plants and algae show this type of life cycle

Intermediary or sporic meiosis

What type of Life Cycle is this describing:

In higher plants (e.g. corn),  the anthers and pistils produce microscopes and megaspores, respectively.