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Asexual Reproduction
creation of genetically identical offspring by a sing parent (no eggs and sperm)
Produce offspring that are genetic copies of the parent and identical to each other (clones)
Sexual Reproduction
reproduction that requires the fusion of gametes (sperm and eggs)
Cell Division
proceeds daughter cells or gametes
cells originate only from preexisting cells
each species carries its own specific genetic information
Cell division involves the separation of sister chromatids and results in two daughter cells, each containing a complete and identical set of chromosomes.
Binary Fission
prokaryotic cells reproduce asexually, binary fission means dividing in half
Contrast the structure and number of prokaryotic and eukaryotic chromosomes
In Prokaryotes, most genes are carries on one circular DNA molecule, with associated proteins constitutes the organisms SINGLE CHROMOSOME
as the cell relocated the one chromosome
the copies move apart
the plasma membrane pieces inward and more cell wall is made, which divides the parent cell into two daughter cells
In Eukaryotes, there are many more genes than prokaryotic cell, and they are grouped into MULTIPLE CHROMOSOMES in the nucleus
Each eukaryotic chromosome contains one long D N A molecule.
Individual chromosomes are visible under a light microscope only when the cell is in the process of dividing; otherwise, chromosomes are thin, loosely packed chromatin fibers too small to be seen
Cell Cycle
interphase + mitotic phase (mitosis + cytokinesis)
Mitosis
Division of nucleus into two identical nuclei
Cytokinesis
Division of the cytoplasm immediately after mitosis
Sister Chromatids
Contains identical DNA
before cells start dividing, the chromosomes duplicate producing sister chromatids
DNA after it has duplicated and has two identical copies (connected most closely at the centromere) The
Chromosomes
DNA structures that carry a cell’s genetic information and are found in the nucleus of eukaryotic cells
Chromatin
DNA (and its associated proteins) in a diffuse, stretched-out form when a cell is not dividing and cannot be seen in a light microscope
The Cell Cycle
is an ordered sequence of events that run from the time a cell is first formed from a dividing parent cell until its own division into two cells
Interphase
cell grows, has high metabolic activity, synthesizes organelles, and performs its normal function. Includes G1 + S + G2 phases
G1
growth and metabolism (DNA in chromatin form)
Synthesis
duplication/replication of DNA (still in chromatin form)
G2 Phase
preparation for cell division (sister chromatids in chromatin form)
Mitosis
distributes duplicated chromosomes into two daughter nuclei (mitosis = division of nucleus)
Mitotic Spindle
made up of microtubules, moves the chromosomes to the middle of the cell
Prophase
chromosomes condense and spindle forms
Double
Pro metaphase
nuclear membranes breaks down and microtubules reach each the chromosomes
single
Metaphase
spindle complete and chromosome lines up in the middle
Double
Anaphase
sister chromatids separate and move to opposite poles of the cell
single
Telophase and Cytokinesis
nuclear envelope forms, chromatin uncoils, cleavage furrow forms
Double
Contrast cytokinesis in plant and animal cells
In animals
cytokinesis occurs when a cell constricts, forming a cleavage furrow
Contracting microfilaments pinch the cell in two like a drawstring
In plants
a membranous cell plate forms and then split the cell in two
vesicles collect in the center and fuse
Growth Factor
a protein that stimulates cells to divide
What is Cancer?
a disease of the cell cycle
the cells divide excessively to form masses called tumors. They do not need cell cycles
Benign Tumor
the abnormal cells remain at the original site
Malignant Tumor
the abnormal cells spread to nearby tissues and invade other parts of the body. This is cancer and the spread of cancer cells beyond the original site is metastasis
Moisis
the division of a single diploid nucleus unto four haploid nuclei (gametes)
Homologous Pairs
The somatic (body) cells of each species contain a specific number of chromosomes; for example, human cells have 46, consisting of 23 pairs of homologous chromosomes - one inherited from your mother, one from your father
Homologous Chromosomes
one inherited from your mother, one from your father
Diploid Cells
Cells with two sets of homologous chromosomes (46 chromosomes in humans (one from each parent)
Gametes
eggs and sperm, are haploid cells with a single set of chromosomes (23 chromosomes)
Meiosis
chromosome duplication, but the cell DIVIDES TWICE to four four daughter cells (gametes)
Crossing Over
homologous chromosomes exchange corresponding segments
In Meiosis I
the haploid cells with duplicated chromosomes
•separates the members of each homologous pair and produces two daughter cells, each with one set of chromosomes.
starts with the pairing of homologous chromosomes
Meiosis II
the sister chromatids separate and create four haploid cells
Know the different between Mitosis and Meiosis
–Mitosis produces two genetically identical diploid somatic daughter cells.
–Meiosis produces four genetically unique haploid gametes.
How are they similar
Both mitosis and meiosis begin with diploid parent cells that have chromosomes duplicated during the previous interphase.
Crossing Over
an exchange of corresponding segments between nonsister chromatids of homologous chromosomes
What is a Karyotype
it is a Photographic inventory of an individual chromosomes
How do you prepare them?
•white blood cells are isolated, stimulated to grow, arrested at metaphase stained to reveal band patterns, and
photographed under a microscope
The chromosomes are arranged into ordered pairs so that any chromosomal abnormalities can be detected
What is nondisjunction?
•An abnormal chromosome count is the result of nondisjunction, which can result when members of a chromosome pair fail to separate during meiosis:
–the failure of a pair of homologous chromosomes to separate during meiosis I or
–the failure of sister chromatids to separate during meiosis I IWhic
Which chromosomal abnormality causes Down Syndrome?
Trisomy 21 results in Down syndrome
The copies fo chromosome 21 fail to separate during meiosis
What are the sex chromosomes of individuals with Turner Syndrome and Klinefelter Syndrome?
Klinefelter Syndrome (male)- XXY
Turner Syndrome (female)- XO
Describe the 4 types of changes in chromosome structure due to chromosome breakage
Chromosome breakage can lead to rearrangements—deletions, duplications, inversions, and translocations—that can produce genetic disorders or, if the changes occur in somatic cells, cancer
Who was Mendel? What organism did Mendel study?
He was the guy who studied the pea plant
Heredity
•is the transmission of traits from one generation to the next.
–You inherit traits from your parents
Genetics
**(**the scientific study of heredity) began with Gregor Mendel’s experiments.
–A heritable feature that varies among individuals is called a character.
–Mendel crossed pea plants and traced traits(variants of a character) from generation to generation.
Distinguish between true-breeding, hybrids, the P generation, F1 generation, and F2 generation
True-Breeding-
Hybrids- offspring of two different varieties
P generation- parent generation
F1 generation-first generation of offspring
F2 generation- offspring of F1 generation
Alleles
alternative versions of gene that account for variations in inherited characters
Homozygous
An organism that has two identical alleles for a gene
Heterozygous
an organism that had two different alleles for a gene
Dominant Allele
if the two alleles of an inherited pair differ (heterozygous) and one determines the organism’s appearance
Recessive Allele
one of the alleles has no noticeable effect on the organism’s appearance
Law of Segregation
A sperm or egg carries only one allele for each inherited character because allele pairs separate (segregate) from each other during the production of gametes (meiosis).G
Genotype
the different variations in the punnet square
Ex: PP, Pp, Yg
Examples- BB; homozygous dominant
Bb; Heterozygous
bb; homozygous recessive
Phenotype
what it looks like
Ratio example- 3 purple : 1 white
Monohybrid Cross
a cross between two individuals that are heterozygous for one character
Dihybrid Cross
a cross between two organisms that are each heterozygous for two characters being followed
Mendel’s Law of Independent Assortment
the alleles of a pair segregate independently of other allele pairs during gamete formation
What is the purpose of a test cross
it can reveal the unknown genotype, a mating between an individual of unknown genotype and a homozygous recessive individual,
Pedigrees
a family tree of traits of parents and children across generations
we use this to deduce the genetic information, and can also determine individual genotypes
The ABO Blood Group
this phenotype in humans is controlled by three alleles that produce a total of four phenotypes
Codominant
•Both alleles are expressed in heterozygous individuals (IAIB), who have type A B blood
Pleiotropy
occurs when one gene influences multiple characters
Sickle-cell Disease
is a human example of pleiotropy.
–This disease affects the type of hemoglobin produced and the shape of red blood cells, andcauses anemia and organ damage.
–Sickle-cell and nonsickle alleles are codominant.
–Carriers of sickle-cell disease have increased resistance to malaria.
Polygenic Inheritance
which a single phenotypic character results from the additive effects of two or more genes on a single phenotypic character
ex; human height
Linked Genes
–are located close together on the same chromosome and
–tend to be inherited together.
–These genes do not follow the Law of independent assortment
Crossing Over
homologous chromosomes produces new combinations of alleles in gametes
•Linked genes can be separated by crossing over, forming recombinant gametes.
•The percentage of recombinant offspring among the total is the recombination frequency.
Sex Chromosomes
Males- XY
Female- XX
–The Y chromosome has genes for the development of testes, whereas an absence of the Y allows ovaries to develop.
•In humans, however, if this gene is not turned on, ovaries develop even in an XY embryo
•In humans, sex is determined by the interactions of several proteins produced by different genes, including autosomal (non-sex chromosome) genes.
–Because of this complexity we now know that sex in humans is not a binary state, and has many variations
Sex-linkes gene
a gene located on either sex chromosome
X-linked Gene
control trains unrelated to sex
–Red-green colorblindness
–Hemophilia – lack protein required for blood clotting
Recessive Disorders
Must be homozygous for the allele
Albinism, Cystic Fibrosis, Phenylketonuria (P K U), Sickle-cell disease, Tay-Sachs disease
Dominant Disorders
can be heterozygous because it is dominant
Achondroplasia, Huntington’s disease, Hypercholesterolemia
Experiments leading up to and including the description of DNA with the following scientist(s): Watson and Crick, Rosalind Franklin, Hershey and Chase, Chargaff
Watson and Crick-were the first to the finish line (their paper showing the model of DNA was published in 1953), their model gave new meaning to the words genes and chromosomes. The genetic information in a chromosome is encoded in the nucleotide sequence of D N A.
Rosalind Franklin- had taken an x-ray image of DNA and knew that the sugar-phosphate backbone was on the outside and the nitrogenous bases were on the inside
Hershey and Chase- able to show that certain bacteriophages (or phages, bacterial viruses) reprogram host cells to produce more phages by injecting their DNA
Chargaff-was a biochemist and had discovered that the amount of C in DNA equaled the amount of G
What is the monomer of nucleic acids DNA and RNA? What are the 3 components of the monomer? What are the nitrogenous bases?
•D N A and R N A are nucleic acids consisting of long chains (polymers) of chemical units (monomers) called nucleotides.
One of the two strands of D N A is a D N A polynucleotide, a nucleotide polymer (chain)
•A nucleotide is composed of a nitrogenous base, five-carbon sugar, and phosphate group.
•Each type of D N A nucleotide has a different nitrogen-containing base: adenine (A), cytosine (C), thymine(T), and guanine (G)
The nucleotides are joined to one another by
a sugar-phosphate backbone
Nitrogenous bases of DNA
Functional groups determine which two bases can form hydrogen bonds
The full name for DNA is deoxyribonucleic acid, with nucleic referring to what?
DNA’s location in the nuclei of eukaryotic cells
RNA (ribonucleic acid)
–Is single stranded
–uses the sugar ribose (instead of deoxyribose in D N A) and
has a nitrogenous base uracil (U) instead of thymine
DNA replication
•starts with the separation of D N A strands.
•Enzymes then use each strand as a template to assemble new nucleotides into a complementary strand.
•requires the coordination of more than a dozen enzymes and other proteins
•DNA is untwisted and the two new strands are made roughly simultaneously
•Human cells have more than 6 billion base pairs but can replicate in a few hours
•Accurate - only about one nucleotide in several billion is mispaired
Semiconservative model
–The two D N A strands separate.
–Each strand then becomes a template for the assembly of a complementary strand from a supply of free nucleotides.
–Each new D N A helix has one old strand with one new strand (half of the parent molecule is conserved in each ‘daughter’ molecule).
DNA polymerase
the cell synthesizes one daughter strand as a continuous piece
DNA Ligase
The other strand is synthesized as a series of short pieces, which are then connected by this enzyme
Transcription
(Nucleus)
•is the synthesis of R N A under the direction of DNA
Translation
(cytoplasm)
is the synthesis of proteins under the direction of RNA
What is a gene?
•is defined as a region of DNA that can be expressed to produce a functional product that is either a polypeptide or an R N A molecule.
–Recall that a polypeptide is a polymer of a protein
Triplet Code
The genetic instructions for the amino acid sequence of a polypeptide chain are written in DNA and RNA as a series of non overlapping three-base “words” called codons.
Be able to translate DNA to RNA
AAACCGGCAAAA
UUUGGCCGUUUU
The genetic code
•is instructions contained in a gene that tell a cell how to make a specific protein
–The amino acid translation of the nucleotide triplets
•Nearly all organisms use an identical genetic code to convert the m R N A codons transcribed from a gene to the amino acid sequence of a polypeptide.
RNA polymerase
•joins them along one strand of the D N A, following the base-pairing rules.
–A specific nucleotide sequence called a promoter acts as a binding site for R N A polymerase and determines where transcription starts.
In the nucleus, the D N A helix unzips, and R N A nucleotides line up
Messenger RNA (mRNA)
conveys genetic messages from D N A to the translation machinery of the cell (ribosomes).
Before leaving the nucleus as m R N A, eukaryotic transcripts undergo two modifications:
the product of transcription, carries genetic information from DNA to a ribosome
RNA splicing
introns (noncoding segments of R N A) are spliced out “intragenic region”,
exons (the parts of a gene that are expressed) are spliced together
Multiple polypeptides from a single gene
Cap and Tail
are added to the ends of the m R N A
§Facilitate export out of the nucleus, protect the mRNA from degradation, and help the ribosome bind to the mRNA.
Transfer RNA (tRNA)
A ribosome attaches to the m R N A and translates its message into a specific polypeptide,
tRNAs transfer amino acids from the ‘cytoplasmic pool’ and add them to the growing polypeptide
–Each t R N A is a folded molecule bearing a base triplet called an anticodon on one end and a specific amino acid attachment site at the other end.
needed for translation. Carries a specific amino acid (coded by mRNA) to the ribosome
Ribosomes
are structures in the cytoplasm that coordinate functioning of m R N A and t R N A and catalyze the synthesis of polypeptides
Ribosomal RNA (rRNA)
Ribosomes are made of rRNA and proteins and have binding sites for tRNA and mRNA
RNA that (combined with proteins) makes up ribosomes, which translate mRNA into proteins
Translation brings together
–mRNA,
–a tRNA bearing the first amino acid, and
–the two subunits of a ribosome.
The flow of genetic information
•DNA transcribed to RNA in the nucleus
•RNA is processed (mRNA) and exits the nucleus (in eukaryotes)
•mRNA and tRNA with a specific amino acid are used by the ribosome to create a polypeptide
•Polypeptide folds into 3-dimensional tertiary structure which determine its function
Mutations
•are changes in the genetic information of a cell or virus, caused by errors in D N A replication or recombination, or by physical or chemical agents called mutagens.
–Examples of mutagens: high energy radiation such as X-rays or UV light, tobacco products, radioactive substances
•Substituting, inserting, or deleting nucleotides alters a gene, with varying effects.
Elongations
Elongation continues until a stop codon reaches the ribosome’s A site