José A. Cardé-Serrano, PhDBiol 223 – GenéticaUniversidad Adventista de las Antillas

Introducción a la Biología Molecular: células y cromosomas

Discusión y repaso de Mitosis y Meiosis

Contraste de Procariotas y Eucariotas

Discusión de Sistemas Modelos para Genética.

Cells and ChromosomesMitosisMeiosisGenetics in the Laboratory: An

introduction to Some Model Research Organisms

In both prokaryotic and eukaryotic cells, the genetic material is organized into chromosomes.

Cytoplasm—the inside of a cell Water Hydrophilic and Hydrophobic Molecules Carbohydrates Lipids Proteins, including enzymes Membrane—made of lipids and proteins Nucleic acids Organelles

Double-stranded DNA with associated proteins and sometimes RNA

Prokaryotic cells contain one circular chromosome plus smaller plasmids

Most eukaryotic cells contain several large linear chromosomes

DiploidHaploidPolyploid and aneuploidSomatic cellsGerm lineGametesCentromereTelómero

A mother cell divides to produce two daughter cells.

The mother cell’s chromosome is duplicated prior to fission.

Each daughter cell receives one copy of the chromosome.

Clone—a population of genetically identical cells.

Colony—a visible mass of cells.

Cells, the basic units of all living things, are enclosed by membranes.

Chromosomes, the cellular structures that carry the genes, are composed of DNA, RNA, and protein.

In eukaryotes, chromosomes are contained within a membrane-bounded nucleus; in prokaryotes they are not.

Eukaryotic cells possess complex systems of internal membranes as well as membranous organelles such as mitochondria, chloroplasts, and the endoplasmic reticulum.

Haploid eukaryotic cells possess one copy of each chromosome; diploid cells possess two copies.

Prokaryotic cells divide by fission; eukaryotic cells divide by mitosis and cytokinesis.

Eukaryotic chromosomes duplicate when a cell’s DNA is synthesized; this event, which precedes mitosis, is characteristic of the S phase of the cell cycle.

When eukaryotic cells divide, they distribute their genetic material equally and exactly to their offspring.

Spindle Microtubule

organizing centers (MTOCs)

Centrosomes and centrioles

Pericentriolar material

Aster

As a cell enters mitosis, its duplicated chromosomes condense into rod-shaped bodies (prophase).

As mitosis progresses, the chromosomes migrate to the equatorial plane of the cell (metaphase).

Later in mitosis, the centromere that holds the sister chromatids of a duplicated chromosome together splits, and the sisters chromatids separate (or disjoin) from each other (anaphase)

As mitosis comes to an end, the chromosomes decondense and a nuclear membrane reforms around them (telophase).

Each daughter cell produced by mitosis and cytokinesis has the same set of chromosomes; thus, daughter cells are genetically identical.

Sexual reproduction involves a mechanism that reduces the number of chromosomes by half.

Chromosomes condense

Each chromosome has two sister chromatids

Synapsis of homologous chromosomes

Synaptonemal complex

Chromosomes condense further

Bivalent Tetrad

Crossing over occurs

Paired chromosomes separate slightly but are in contact as chiasmata

Nuclear envelope fragements

Spindle fibers attach to kinetochores

Chromosomes move to central plane in pairs

Paired chromosomes are oriented toward opposite poles

Terminalization: chiasmata move toward telomeres

Chromosome disjunction (separation of paired chromosomes)

Separated homologues move toward opposite poles

Chromosomes reach the poles; nuclei forms

Spindle apparatus is disassembled

Daughter cells separated by membranes

Chromosomes decondensed

Each chromosome still has two sister chromatids

Chromosomes condense

Chromosomes attach to a new spindle apparatus

Sister chromatids are attached to spindle fibers from opposite poles

Chromosomes align at equatorial plane

Centromeres split

Chromatid disjunction—sister chromatids move toward opposite poles

Separated chromatids gather at poles; daughter nuclei form

Each chromatid is now called a chromosome

Each daughter nucleus contains a haploid set of chromosomes

The haploid daughter cell are separated by cytoplasmic membranes

Maternal and paternal homologues synapse, then disjoin.

Different pairs disjoin independently.

Homologous chromosomes exchange material by crossing over

Diploid eukaryotic cells form haploid cells by meiosis, a process involving one round of chromosome duplication followed by two cell divisions (meiosis I and meiosis II).

During meiosis I, homologous chromosomes pair (synapse), exchange material (cross over), and separate (disjoin) from each other.

During meiosis II, chromatids disjoin from each other.

In many organisms, the haploid products of meiosis develop directly into gametes.

In plants, the products of meiosis divide mitotically to form haploid gametophytes.

The gametophytic phase of a plant’s life cycle alternates with the sporophytic phase, which is diploid; meiosis occurs in the sporophyte.

Geneticists focus their research on microorganisms, plants, and animals well suited to experimentation.

Rod-shaped bacterium

Molecular Genetics

4.6 106 base pairs

4288 protein-coding genes

Single circular chromosome

Bacteriophages

Unicellular fungus 16 linear

chromosomes 12 106 base pairs 6268 genes Reproduces sexually

and asexually Model system por

Genetics, Cell cycle, RNA studies

Insect Anatomically

complex 170 106 base

pairs 13,792 genes Model system

for Genetics, Develomental and Hox Genes

Model for animal development

Hermaphroditic 100 106 base

pairs 20,512 genes

Biomedical research

Comparative genomics

2.9 109 base pairs

25,396 genes Model system for

Genetics, KO genes, Immunology

Model for vertebrate development

Transparent eggs; external fertilization

1.6 109 base pairs

23,524 genes

Self-fertilizing Model for

agriculturally significant plants

157 106 base pairs

27,706 genes

Cell culture DNA Cloning The Human

Genome Project 3.2 109 base

pairs 20,000 to 25,000

genes

The bacterium E. coli is the premier prokaryote for genetic analysis.

Model eukaryotes include yeast (S. cerevisiae), a fruit fly (D. melanogaster), a round worm (C. elegans), the mouse (M. musculus), the zebrafish (D. rerio), and a fast-growing plant (A. thaliana).

Techniques such as cell culture and DNA cloning have made it possible to study the genetic material of human beings and many other organisms.

En las células somáticas del ratón casero hay 40 cromosomas:

A) Cuantos cromosomas recibe el ratón de su padre?

B)Cuantos cromosomas autosomales (no sexuales) hay en un gameto de ratón?

C) Cuantos cromosomas sexuales habra en un óvulo de ratón?

D) Cuantos cromosomas autosomales (no sexuales) hay en una célula somática de una hembra?