Genetics
the study of how traits are inherited from one generation to the next
Gene
basic unit of heredity
Chromosomes
location of genes on DNA
Alleles
alternative forms of genes when it exists in more than one form
Genotype
genetic makeup of an individual
Phenotype
physical manifestation of the genetic makeup
Mendelian Genetics
developed the basic principles of genetics through his experiments with the garden pea
Crosses
true-breeding individuals (which, if self-crossed, produce progeny only with the parental phenotype) with different traits, mated them, and statistically analyzed the inheritance of the traits in the progeny
Mendel's First Law: Law of Segregation (Four Principles)
1) Genes exist in alternative forms. A gene controls a specific trait in an organism.
2) An organism has two alleles for each inherited trait, one inherited from each parent
3) The two alleles segregate during meiosis, resulting in gametes that carry only
Dominant Allele
-expressed allele
-usually assigned capital letters
Recessive Allele
-silent allele
-usually assigned capital letters
Homozygous
organisms that contain two copies of the same allele
Heterozygous
organisms that carry two different alleles
Mendel's Law of Dominance
dominant allele is expressed in the phenotype
Monohybrid Cross
only one trait is being studied in this particular mating
Parental (P Generation)
individuals being crossed
Filial (F generations)
progeny generations
Punnet Square Diagram
-one way of predicting the genotypes expected form a cross
-genotypes are determined by looking at the intersections of the grid
-indicates all potential progeny genotypes and the relative frequencies of the different genotypes and phenotypes can be easil
Testcross
-diagnostic tool to determine the genotype of an organism
-Only with a recessive phenotype can genotype be predicted with 100% accuracy
-if dominant phenotype is expressed, the genotype can be either homozygous dominant or heterozygous
-used to determine
Backcross
an organism with a dominant phenotype of unknown genotype (Ax) is crossed with a phenotypically recessive organism
Mendel's Second Law: Law of Independent Assortment
-genes on the same chromosome will stay together unless crossing over occurs
-crossing over exchanges information between chromosomes and may break the linkage of certain patterns
Dihybrid Cross
the parents differ in two traits, as long as the genes are on separate chromosomes and assort independently during meiosis
Non-Mendelian Inheritance Patterns
include incomplete dominance, and codominance
Incomplete Dominance
progeny phenotypes are apparently blends of the parental phenotypes
Codominance
-occurs while multiple alleles exist for a given gene and more than one of them is dominant
-expression of both dominant alleles are simultaneous
-ex: ABO blood group
Autosomes
pairs of homologues in sexually differentiated species
Sex Linked
-genes that are located on the X or Y chromosome
-in humans, most are located on the X
Sex Linked Recessives
recessive genes that are carried on the X chromosome will produce the recessive phenotypes whenever they occur in men because no dominant allele is present to mask them
-ex: hemophilia and color blindness
Drosophila Melanogaster
fruit fly
-produces often (short life cycle)
-reproduces in large numbers (large sample size)
-chromosomes (especially in the salivary gland) are large and easily recognizable in size and shape
-its chromosomes are few (4 pairs, 2n=8)
-Mutations occur rel
Environmental Factors
can often affect the expression of a gene
-interaction betwen the enironment and the genotype produces the phenotype
DNA
-deoxyribonucleic acid
-contains information coded in the sequence of its base pairs, provding the cell with a blueprint for protein synthesis
-regulate all life functions
-has the ability to self replicate
-basis of heredity
-mutable
Heredity
self replication ensures that its coded sequence will be passed on to successive generations
Mutable
can be altered under certain conditions, altering the corresponding characteristics in the organism
Nucleotide
-basic unit of DNA, which is composed of deoxyribose (a sugar) bonded to both a phosphate group and a nitrogenous base
-bases: purines and pyrimidines
Purines
adenine and guanine
Pyrimidines
Cytosine and thymine
Double-Stranded Helix
-sugar-phosphate chains on the outside of the helix and the bases on the inside
-C-G, T-A
-AKA Watson Crick DNA model
DNA Replication
double stranded DNA molecule unwinds and separates into two single strands
Complementary Base-Pairing
each strand of DNA that is a template in the synthesis of two new daughter helices
Semiconservative
Each new daughter helix contains an intact strand from the parent helix and a newly synthesized strand
Leading Strand
Daughter strand that is continuously synthesized by DNA polymerase in the 5'->3' direction
Lagging Strand
synthesized discontinuously in the 5'->3' direction (since DNA polymerase synthesizes only in that direction) as a series Okazaki fragments
Okazaki fragments
short segments from lagging strand
Genetic Code
-language of DNA consists of four letters: A,T,C,G
-language of proteins consists of 20 "words": 20 amino acids
-universal for almost all organism
Triplet Code
DNA language must be translated by mRNA in such a way as to produce the 20 words in the amino acid language
Codons
base sequence of mRNA is translated as a series of triplets
Synonyms
degeneracy/redundancy of the genetic code since there are 64 different codons and only 20 amino acids
RNA
-ribonucleic acid
-polynucleotide structurally similar to DNA except that its sugar is ribose
-contains uracil instead of thymine
-usually single stranded
-found in both nucleus and cytoplasm
-several types are involved with mRNA, tRNA, and rRNA
Messenger mRNA
-carries the complement of a DNA sequence and transports it from the nucleus to the ribosomes
-assembled from ribonucleotides that are complementary to the "sense" strand of the DNA
-monocistronic
Ribosomes
where protein synthesis occurs
Monocistronic
one mRNA strand codes for one polypeptide
Transfer RNA (tRNA)
small RNA found in the ctyoplasm that aids in the translation of mRNA's nucleotide code into a sequence of amino acids
-brings amino acids to the ribosomes during protein synthesis
Ribosomal RNA (rRNA)
structural component of ribsomes and is the most abundant of all RNA types
-synthesized in the nucleolus
Transcription
the process whereby information coded in the base sequence of DNA is transcribed into a strand of mRNA that leaves the nucleus through nuclear pores. the remaining events of protein synthesis occur in the cytoplasm
Translation
process whereby mRNA codons are translated intoa sequence of amino acids
-occurs in cytoplasm and involves tRNA, ribosomes, mRNA, amino acids, enzymes, and other proteins
tRNA Job
brings amino acids to the ribosomes in the correct sequence for polypeptide synthesis
-recognizes both the amino acid and the mRNA codon
Anticodon
complementary to one of the mRNA codons
Aminoacyl-tRNA synthetase
on amino acid which has an active site that binds to both the amino acid and its corresponding tRNA, ctalyzing their attachment to form an aminoacyl-tRNA complex
Ribosomes
composed of two subunits (consisting of proteins and rRNA), one large and one small, that bind together only during protein synthesis
-have 3 binding sites (for mRNA and two tRNA)
P-site
tRNA binding site for ribosomes to attach to the growing polypeptide chain (peace out site)
A-site
binds to the incoming aminoacyl-tRNA complex (Arriving site)
Polypeptide Synthesis
initiation, elongation, and termination
Start Codon
(AUG) ribosome scans the mRNA until it bonds to this (methionine) and UAC on anticodon of tRNA
Elongation
hydrogen bonds form between the mRNA codon in the A site and its complementary anticodon on the incoming aminoacyl-tRNA complex
Peptide Bond
formed between the amino acid attached to the tRNA in the A site and the fmet attached to the tRNA in the P site
Translocation
the ribosome advances three nucleotides along the mRNA in the 5' to 3' direction and the uncharged tRNA from the P site is expelled, and the peptidyl-tRNA from the A site moves into the P site and completes the cycle
Termination Codons
(UAA, UAG, or UGA) terminates polypeptide synthesis
Polyribosome
structure formed when many ribosomes simultaneously translate a single mRNA molecule
Nondisjunction
-either the failure of homologous chromosomes to separate properly during meiosis I or the failure of sister chromatids to separate properly during meiosis II
-zygote might either have 3 copies of that chromosome (trisomy) or just a single copy (monosomy)
Chromosomal Breakage
May occur spontaneously or be induced by environmental factors
Mutations
-changes in the genetic information of a cell coded in the DNA
-if occured in the somatic cells, it can lead to tumors in an individual
Mutagenic Agents
-induce mutations
-include cosmic rays, X rays, UV rays, and radioactivity
Gene Mutation
-nitrogen bases are added, deleted, or substituted, thus crating different genes; inappropriate amino acids may be inserted into polypeptide chains, and a mutated protein may be produced
Point Mutation
nucleic acid is replaced by another nucleic acid
Silent Mutation
new codon may code for the same amino acid
Missense Mutation
new codon may code for a different amino acid
Nonsense Mutation
new codon may be a stop codon
Frameshift Mutation
nucleic acids are deleted or inserted into the genome sequence (lethal)
Bacterial Genome
consists of a single circular chromosome located in the nucleoid region of the cell
Plasmids
small circular rings of DNA which contain accessory genes
Episomes
plasmids that are capable of integration into the bacterial genome
Bacterial Replication
begins at a unique origin of and proceeds in both directions simultaneously
Binary fission
-reproduction of bacterial cells and proliferate very rapidly under favorable conditions
-asexual prcoess
-3 kinds (transformation, conjugation and transduction)
Transformation
the process by which a foreign plasmid is incorporated into the bacterial chromosome via recombination, creating new inheritable genetic combinations
Plasmid
chromosome fragment
Conjugation
transfer of genetic material between two bacteria that re temporarily joined
Antibody resistance
may be found on the plasmids and transferred into recipient cells along with these factors
Transduction
occurs when fragments of the bacterial chromosome accidentally become packaged into viral progeny produced during a viral infection
Varions
may infect other bacteria and introduce new genetic arrangements through recombination with the new host cell's DNA
Recombination
occurs when linked genes are separated
Transcription
regulation of gene expression and enables prokaryotes to control their metabolism
Operon
consists of structural genes
Operator Gene
the sequence of nontranscribable DNA that is the repressor binding site
Promoter gene
the noncoding sequence of DNA that serves as the initial binding site for RNA polymerase
Regulator Gene
codes for the synthesis of a repressor molecule that binds to the operator and blocks RNA polymerase form transcribing the structural genes
Inducible Systems
system where the repressor binds to the operator, forming a barrier that prevents RNA polymerase from transcribing the structural genes
Inducer-Repressor Complex
complex that can't bind to the operator, thus permitting transcription
Repressible Systems
system where the repressor is inactive until it combines with the corepressor
Bacteriophage
virus that infcts its host bacterium by attaching to it, boring a hole through the bacterial cell wall, and injecting its DNA while its protein coat remains attached to the cell wall and enters the host in either a lytic cycle or a lysogenic cycle
Lytic Cycle
phage DNA takes control of the bacterium's genetic machinery and manufactures numerous progeny, causing the cell to lyse, releasing new virions, each capable of infecting other bacteria
-if initial infection takes place on a bacterial lawn, then very shor
Lyse
cell burst
Virulent
bacteriophages that replicate by the lytic cycle, killing their host cells
Lysogenic Cycle
if the bacterioophage does not lyse its host cell, it becomes integrated into the bacterial genome in a harmless form, lying dorant for one or more generations. the virus mays tay integrated indefinitely, replicating along with the bacterial gneome. howev