must precede cell division. DNA houses all information for reproduction, development and maintenance of the cell and the organism.
information for the production of proteins that perform most of the cells work. Information for the protein sequence is determined by the base sequence. The sum of all genetic information in an organism is included in what we call the genome.
DNA is packaged in...
is long strands of DNA wrapped around proteins.
is a packaged and condensed strand of Chromatin (DNA and Protein). When DNA is replicated two identical copies are made of one chromosome.
Most eukaryotic cells are...
diploid: have pairs of the same chromosome; these pairs represent the homologous pairs (these chromosomes are not identical, they carry the information for the same trait, but alternative forms).
Humans and mammals use chromosomes to determine sex. Males have one X and one Y: females have two Xs.
- The egg contains 23 chromosomes (22 autosomal + 1 X)
- The sperm contains 23 chromosomes (22 autosomal + 1 X or 1 Y)
Orderly display of magnified images of the individuals chromosomes. Cells are arrested at metaphase and magnified.
Two type of Cell Division in most Eukaryotes:
Mitosis (identical) and Meiosis (reductional ). Both are preceded by interphase an intensely active phase where the cell prepares itself for mitosis or meiosis. During interphase DNA is replicated.
The Cell Cycle
- The Cell Cycle lasts 24 hrs. There are three phases:
- 1.Interphase: includes G1, S (duplication of DNA 6of 23.5hrs) and G2 , lasts 23.5 hr
- 2. Mitosis or identity division (nuclear division). Begins with one diploid cell and produces of two identical diploid daughter cells; sister chromatids condense, align themselves,and separate in 4 stages that lasts 30 minutes includes:
- Prophase: (plain to see)·
- Metaphase (middle)·
- anaphase (apart)·
- telophase (two nuclei)
- 3. Cytokinesis (div of the cytoplasm and plasma membrane to form two distinct cells)
- Cytokinesis usually starts in late anaphase or early telophase
- Animals: cleavage furrow formation of a contractile ring.
- In plants cytokinesis occurs by means of a phragmoplast. The phragmoplast forms the cellplate. The phragmoplast is a cylinder consisting of microtubules that are derived from the spindle and aligned between the daughter nuclei. The cell plate consistes of two new plasma membranes and cell walls. It forms between the nuclei and in the center of the phragmoplast. It gradually extends to divide the cell into two daughter cells.
uncontrolled cell division: Genes involved in Cancer
Tumor suppressor genes
act in linked chain of protein activity
SEX CELL DIVISION REDUCES THE CHROMOSOME NUMBER BY HALF.
- Meiosis occurs in Germ Cell (diploid) à Gametes (Sperm and Egg Cell (haploid)
- Oogonia: diploid cells (germ) destined to become egg begins in the ovary
- Spermatogonia: diploid cells (germ) destined to become sperm occurs in the testes.
begins with DNA replication (Interphase), has two nuclear divisions, followed by cytokinesis. Meiosis begins with one diploid cell and produced 4 haploid cells.
Meiosis I, II
- Meiosis I: Includes Prophase I, Metaphase I Anaphase I and Telophase I, no cytokinesis.
- Meiosis I accomplishes the following: Crossing over, separation of homologous chromosomes (note tetrad). DiploidàhaploidMeiosis II: separation of sister chromatid Production of 4 daughter cells (haploid)
occurs when chromosomes fail to separate during meiosis I or meiosis II and causes abnormal chromosome number
3 copies of Chromosome 21 in the diploid cell
XXY sterile male with small testes and breast. A extra Y results in conversion of female to male
XYY . Extra tall, otherwise normal
XXX reduced fertility otherwise normal
XO shorter than average, unusual web of skin between neck and shoulder, reduced fertility
ragment of chromosome removed
one fragment moves to another chromosome giving 2 copies
a fragment moves to another place oriented in the opposite direction
attachment of a chromosome fragment to a non-homologous chromosome
- increases the chances of survival of a species. Is accomplished by
- Mutations (a change in the nucleotide sequence of a gene)
- Sexual Reproduction
- Crossing Over
- Independent Assortment of chromosomes
Life Cycle of Humans and Other Sexual Reproducing Organisms
- Meiosis creates haploid gametes
- Fertilization of gametes produces zygote (diploid cell)
- Trillions of mitotic divisions produce a Baby
- Continued growth, cell specialization and cell death produces an adult
- Once an organism reaches sexual maturity, Sex cells divide by Meiosis to create haploid gametes
are alternative forms of the same gene
are character variations.
is the physical characteristic or “trait.
- is the genetic basis for the trait it represents the combination of alleles you inherit
- Homozygous Dominant
- Homozygous Recessive
- s the father of genetics. His discoveries in genetics were based on work with Pisum sativa (garden pea).
- Characteristics of Pisum sativa
- They can self pollinate
- They can be cross pollinated
- Many of the measurable traits were dominant or recessive
- Mendels First Experiment was a Monohybrid Cross.
The Principle of Segregation
states that pairs of genes segregate (separate) during gamete formation and fusion of gametes at fertilization pairs genes once again. Demonstrated in a monohybrid cross.
The Principle of Independent Assortment
Each pair of alleles segregates independently during gamete formation. Demonstrated during the dihybrid cross. Independent (Random) Assortment of Alleles can be demonstrated in Meiosis.
Albinism, Deafness, Cystic fibrosis, Sicke-cell disease and Tay-Sachs
Achondroplasia, certain types of Alzheimer’s disease, Huntington’s Disease and Hypercholesterolemia
produces intermediate phenotypes. These traits can not completely mask out the effects of the recessive trait. Examples are Sickle-cell, hypercholesterolemia, and In plants it’s the pink flower color in snapdragon.
In typical Mendelian Inheritance 2 alleles determine phenotype. In this case there are > 2 alleles for a trait in a population. Multiallelic inheritance produces a range in phenotypes. In Plants, the varigation patterns on clover leaves “Chevron” is determined by a gene with multiple alleles. In humans, there are four blood groups A, B, AB and O. These groups are derived from 3 alleles: the A, B and O allele.
One gene influences several characteristics. Study the pleitrophic effects of the S-gene in tobacco. The S gene affects the corolla, anther, calyx, leaf, and capsule. In humans sickle cell trait produces pleiotrophic effects.
In this case > 2 alleles determines phenotype. Multiallelic inheritance produces a range in phenotypes. Multialleles determines Skin Color and height
testing people for alleles associated with a particular disorder.
Gene (DNA) first make mRNA the mRNA makes protein. One gene coding sequence produces one protein subunit.
the information on DNA is copied onto a length of mRNA (DNAà mRNA)
Occurs in the nucleus
the polypeptide chain is formed (RNAà protein)
Occurs in the cytoplasm and ribosomes
the triplicate code found on mRNA that codes for each of the 20 amino acids, for start (methionine) and stopGenetic Code is the set of rules by which information encoded in genetic material (DNA or RNA sequences) is translated into proteins (amino acid sequences) by living cells
Determines when a protein is expressed (produced) in a cell
The Signal Transduction Pathway
- is the sequence of events that transmits the messenger into a response.It has 3 steps:
- Reception: this occurs at the plasma membrane when the hormone or other signaling molecule binds to a membrane receptor
- Transduction: activation of a cytoplasmic second messengerExpression: the second messenger activates a transcription faction. The activated transcription factor binds to a control element promoting transcription.
- Translation follows transcription.