Chapter 9- Genetics Flashcards
Genetics
The study of how traits are inherited from one generation to the next
Where are genes located?
Chromosomes
Alleles
An alternative form of a gene
Genotype
Genetic makeup of an individual
Phenotype
Physical manifestation of the genetic makeup
What is Mendel’s first law?
Law of segregation
Mendel’s 4 principles of inheritance
- Genes exist in alternative forms
- Gene= 2 alleles, one from each parents
- Two alleles segregate through meiosis- gametes only carry one allele for one given trait
- Dominant and recessive alleles
What does true breeding mean in terms of Mendelian genetics?
organism must be homozygous for every trait for which it is considered true breeding.
How many traits can be tested by a monohybrid cross at a time?
One at a time
P generation
Parental generation- the individual being crossed
F generation
Filial generation- Progeny of the parental generation
Crossing one homozygous dominant and one homozygous recessive results in a f2 generation of
1:2:1
1 Homozygous dominant
2 Heterozygous dominant
1 homozygous recessive
Testcross
Diagnostic tool to determine genotype of an organism- also known as a backcross
When can a genotype be determined with 100% accuracy?
When a recessive phenotype is being tested
If a dominant phenotype is expressed, the genotype can be either:
Homozygous dominant or hetozygous
In a testcross, the appearance of the recessive phenotype in the progeny indicates that the phenotypically dominant parent is genotypically ________
Heterozygous
What is Mendel’s Second law?
Law of independent assortment
What does the law of independent assortment say?
Genes assort independently during the formation of gametes (meiosis)– as long as genes are on separate chromosomes
Typical pattern for Mendelian inheritance in a dihybrid cross between heterozygotes with independently assorting traits
9:3:3:1
Incomplete dominance
Blend. White+red= pink
Intermediates of the phenotypes of the homozygotes
Codominance occurs when…?
Multiple alleles exist for a given gene and more than one allele is dominant. Each dominant allele is fully dominant when combined with a recessive allele but when combined with another dominant allele, they both show through.
Classic dominance of codominance
Individuals with IA and IB blood are group AB because both IA and IB are dominant
Three alleles of ABO blood group
IA
IB
i
True or false: the two members of each of the chromosome are the exact same shape
FALSE. All the autosomal ones are but not the sex chromosomes
Central dogma
DNA-RNA= transcription RNA-Proteins= translation
Nucleotide
The basic structure of DNA- composed of deoxyribose bonded to a phosphate group and a nitrogenous base.
Two types of bases
Purines and pyrimidines
Purines
Adenine, Guanine
Pyrimidines
Cyrosine and thymine
The phosphate and sugar form a chain with the bases and are arranged as: ________
side groups off the chain
Double stranded helix is arranged with ____
The sugar-phosphate chains on the outside of the helix and the bases on the inside.
Nucleotides are bonded by
Hydrogen bonds
T always forms __hydrogen bonds with __
G always forms __ hydrogen bonds with __
2 A
3 C
Each strand of a double helix acts as a template for ____
complementary base-pairing in the synthesis of two new daughter helices.
Semiconservative replication
Each new DNA helix is one old strand and one new
Leading strand
Continually synthesized by the DNA polymerase in a 5’-3’ direction
Lagging strand
Synthesized discontinuously in the 5’-3’ direction as okazaki pragments
DNA polymerase only synthesized new strands in the ___ direction
5’-3’
Codons
The base sequence of mRNA in translation is a series of triplets called codons
True or false: the genetic code is universal for almost all organisms?
True
How many different codons are possible?
64 but there are only 20 amino acids- hence some codons code for the same amino acids- called degenerate or redundacy of the genetic code
How is RNA different the DNA?
- Sugar is ribose
- Contains Uracil instead of thymine
- Single stranded
RNA can be found in both___
the nucleus and cytoplasm
Types of RNA
mTNA, tRNA, rRNA
mRNA
Messenger RNA -Messenger RNA (mRNA) is synthesized from a gene segment of DNA.The messenger RNA carries the code into the cytoplasm where protein synthesis occurs.
mRNA is assembled from_____
ribonucleotides that are complementary to strand of DNA
One mRNA codes for __ polypedtide
one. This is called monocistronic
Is DNA code for amino acid is AAC, the mRNA is ___
UUG
tRNA
Transfer RNA- small RNA found in the cytoplasm that aids in the translation of mRNAs nucleotide code into a sequence of amino acids. Brings amino acids to the ribosomes during protein synthesis.
There is atleast ___ type of tRNA for each amino acid
1
rRNA
Ribosomal RNA is a structure component of ribosomes and is the most abundant type of RNA. Carries the enzymes necessary for protein synthesis
Where is rRNA synthesized
Nucleolus
Transcription
Process whereby information coded in the base sequence of DNA is transcribed into a strand of mRNA that leaves the nucleus through nuclear pores
After transcription, the remaining events of protein synthesis occur in the
cytoplasm
Translation
Process whereby mRNA codons are translated into a sequence of amino acids.
Translation occurs in the ___ and involves ___, ___, ____, _____________, and ______
tRNA, ribosomes, mRNA, amino acids, and enzymes
tRNA recongized both the ___
amino acid and mRNA codon.
Anticodon
in the tRNA– is complementary to one of the mRNA codons
Structure of tRNA
one end- anticodon
Other end- site of amino acid attachment
Aminoacyl-tRNA synthetase
On each amino acid. Has an active site that binds to both amino acid and its corresponding tRNA
Catalyzes formation of aminoacyl-rTNA complex
Ribosomes are composed of…
two subunits, one large and one small
When do the two subunits of a ribosome bind together?
During protein synthesis
How many binding sites do Ribosomes have and what are they?
A total of three binding sites
One for mRNA
two for tRNA
The two binding sites for tRNA on a ribosome are called what? What are they?
P site- peptidyl-tRNA bdining site
A site- aminoacyl-tRNA complex binding site
P site
binds to the tRNA attached to the growing polypeptide chains
A site
Binds to the incoming aminoacyl-tRNA complex
E site
where uncharged tRNA leaves
3 stages of polypeptide synthesis
- Initiation
- Elongation
- Termination
When does synthesis begin?
When the ribosome binds to the mRNA near its 5’ end-
During initiation, what base pairs with the start codon?
Methionine tRNA
What happens during elongation?
Peptide bond is formed between the amino acid attached to the tRNA in the A site and the amino acid attached to the tRNA in the P site
After peptide bond formation, a ribosome carried uncharged tRNA in the P site and peptidyl-tRNA in the A site
Cycle is completed by translocation
Translocation
Ribosome advances 3 nucleotides along the mRNA in the 5’-3’ direction
The uncharged tRNA from P site is expelled and the peptidyl tRNA from the A site moves into the P side.
Ribosome then has an empty A site ready for entry
Nondisjunction
Failure of homologous chromosomes to separate properly during meiosis II
can lead to trisomy or monosomy
Trisomy
2N+1
3 copies of chromosome
monosomy
2N-1
single copy of chromosome
Downs Syndrome is caused by
Trisomy of chromosome 21
True or false: nondisjunction of sex chromosomes can also occur
True
Chromosomal breakage
occur spontaneously or can be induced by environmental factors such as mutagenics and X rays
Mutations
Changes in the genetic information of a cell coded in the DNA
Mutations in the somatic cells can lead to
tumors in the individual
Mutations that occur in the sex cells/ gametes can be
transmitted to the offspring
Most mutations occur in regions of DNA that..
do not code for proteins and are silent, hence not expressed in the phenotype
Mutations that do change the sequence of amino acids in proteins are most often ____ and ______
recessive and deleterious
Mutagenic agents
induce mutations. Also called carcinogenic
Types of mutagenic agents
Cosmic rays, x rays, UV rays, and radtioactivity and colchicine, mustard gas
In gene mutation, nitrogen caes are _____, _____, or ______. This alters the__________________
added, deleted or substituted. This alters the amino acid sequence, may produce mutation
Point mutation
a nucleic acid is replaced by another nucleic acid- usually involved 1-3 nucleotides. Length of the genome does not change
Three possible results on a codon as a consequence of a point mutation
- The new codon may code for the same amino acid (silent mutation)
- The new codon may code for a different amino acid (missense mutation)
- The new codon may be a stop codon (nonsense mutation)
Frameshift mutation
Nucleic acids are deleted or inserted int o the genome sequence.
Freq. Lethal
Throws off the entire sequence of codons from that point
Length of genome changes
PKU
phenylketonuria- a molecular disease caused by the inability to produce the proper enzyme for the metabolism of phenylalanite
Is a type of hyperphenylaninemia
A degradation product accumulates
Individuals cannot consume food with aspartame
Sickle-cell anemia
Red blood cells become cresent-shaped because they contain defective hemoglobin– which carries less oxygen
How is sickle-cell anemia caused?
Substitution of valine for glutamic acid because of a single base-pair substitution in the gene coding for hemoglobin
T/F: heredity systems exist outside the nucleus
True. Example: cytoplasmic inheritance
DNA is found in chloroplasts, mitochondria and other cytoplasmic bodies
Plasmids
Cytoplasmic DNA that regulates drug resistance.
contain one or more genes
Bacterial genome
Consists of single circular chromosome located in the nucleoid region of the cell
True or false: Many bacteria contain plasmids
True
What are plasmids in bacteria?
Circular rings of DNA that contain accessory genes
Episomes
plasmids that are capable of integration into the bacterial genome
Replication of bacterial chromosome begins at a..
Unique origin of replication and proceeds in both directions simultaneously
DNA is synthesized in bacteria in the ___’ - ___’ direction
5’ to 3’
Binary fission
How bacterial cells reproduce
asexual process
Three mechanisms by which bacteria increase genetic variance of a population:
transformation, conjugation, and transduction
Transformation
Process by which a foreign chromosome fragment (plasmid) is incorporated into the bacterial chromosome via recombination, creating new inheritable genetic combinations
Conjugation
sexual mating in bacteria- transfer of genetic material between two bacteria that are temporarily joined
How is genetic material transferred during conjugation?
Conjugation bridge is formed and genetic material is passed between the donor male (+) and recipient female (-)
What kind of bacteria are capable of conjugating?
bacteria containing plasmids called sex factors
F Factor
in E. Coli bacteria
F+ = bacteria containing this factor
F- = bacteria not containing this factor
During conjugation F+ cell replicated F factor and donates it to F- cells
Antibody resistance may be found on the…
plasmids and transferred into recipient cells along with sex factors
Hfr cells
Cells that have a high frequency of recombination
Sometimes, the sex factors become a part of the genome and the whole chromosome replicated. Before it can be transferred to the recipient, it breaks. The part that’s transferred makes novel combination with parts that are already there,
What is transduction?
Occurs when fragments of the bacterial chromosome accidentally become packaged into viral progeny during a viral replication– called virions
What do virions do?
May infect other bacteria and introduce new genetic arrangements through recomb. with new host cell’s DNA.
The closer two genes are to one another on a chromosome, the more likely they are to _____ as a result of virions
Transduce
Recombination
When linked genes are separated— ocurs by breakage and rearrangements of adjacent regions of DNA when organisms carrying different genes or alleles for the same traits are crossed.
Regulation of gene expression
transcription
Regulation of transcription is based on the accessibility of ____________ _________
RNA polymerase to the genes being transcribed
Regulation of transcription is directed by an ___
operon
What does an operon consist of?
Structural genes, an operator region and a promoter region on the DNA before the protein coding genes
What contains the sequences of DNA that code for proteins?
Structural genes
Operator
Sequence of nontranscribable DNA that is the repressor binding site
Promoter
Noncoding sequence of the DNA that serces 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 from transcribing the structural genes
Inducible systems
Require an inducer for transciption to occur
Repressible systems
Are in a constant state of transcription unless a corepressor is present to inhibit transcription
What happens in an inducible system?
The repressor binds to the operator- acts as a barrier for RNA polymerase
What must happen for transcription to occur in an inducible system?
An inducer must bind to the repressor, forming an inducer-repressor complex
Can the inducer-repepressor complex bind too the operator?
No, hence this promotes transcription
What typically codes for an enzyme?
The structural genes
The inducer is usually the:
substrate or substrate derivative on with the enzyme acts upton
When the inducer is present
enzyme is synthesized if not then enzyme not synthesized
Repressible system- the repressor is inactive until
combined with corepressor
The repressor can bind to the operator and prevent transcription only when it has ___
Formed a repressor-corepressor complex
Corepressor are often the end-products of the
biosynthetic pathway that they control
Proteins produced are said to be ____ because ________________________
repressible because they are normally bring synthesized, transcription and translation only stop when corepressor is synthesized
Constitutive enzyme
Always being synthesized– operons containing mutations such as deletions or whose regulator genes code for defective repressors
incapable of being turned off
Bacteriophase
virus that infects its host bacterium by attaching to it- makes a hole through cell wall and injects its own DNA
A bacteriophase’s protein coat remains
attached to the cell wall
Once a bacteriophage is inside of tis host, it
enter the lytic or a lysogenic cycle
Lytic cycle
Phase DNA takes control of bacterial DNA machinary
Bacterial cell wall lyses and releases new virions- which can infect other bacteria
Virulent
bacteriaphages that replicate using lytic cycle and kill their host cells
Lysogenic cycle
If bacteriophage does not lyse host cell, it becomes integrated into the bacterial genome
harmless (provirus) dormant
As a result of env. circumstances or spontaneously, a provirus can
enter lytic cycle
True or false: bacteria containing proviruses are normally resistant to further infection (super infection) by similar phages
TRUE
