Genetics Flashcards
Gene
the basic unit of heredity. Composed of DNA and are located on chromosomes
Alleles
When a gene exists in more than one form, the alternate forms is called alleles.
An organism has two alleles for each trait. one from each parent
Genotype
an individuals genetic makeup
Phenotype
Physical manifestation of a individuals genetic make up
Mendelian Genetics
in 1860s Gregor Mendel developed the basic principles of genetics with the garden pea.
Created Law of Segregation, Law of Independent assortment
True breeding
which if self crossed produce progeny only with the parental phenotype
Law of segregation
two alleles segregate during meiosis, resulting in gametes that carry only one allele for any given trait.
Mendel’s Law of dominance
If two alleles in an organism are different only one will be fully expressed and the other will be silent. The expressed allele is dominant. The silent is recessive.
Homozygous
organisms that contain two copies of the same allele
Heterozygous
organisms that carry two different alleles. The dominant allele appears in the phenotype
Monohybrid Cross
only one trait is being studied in a mating.
P generation
Parental generation being mated will be homozygous for each allele
F generation
filial generation is the progeny being created from the P generation. each generation is numbered sequentially
Punnett square diagram
one way of predicting possible genotypes expected from a cross. indicates all the potential progeny genotypes and relative frequencies.
Test cross/ back cross
only with a recessive phenotype can genotype be predicted with 100% accuracy. Due to it must be homozygous. an organism with a dominant phenotype of unknown genotype (Ax) is crossed with a phenotypically recessive organism (aa). The progeny will dictate if the dominant phenotype is heterozygous or homozygous.
Dihybrid cross
the parents differ in two traits. as long as the genes are independently assorted during meiosis and on separate chromosomes.
Mendel’s Law of independent assortment
the pattern of traits being transmitted to offspring independently.
Mendelian F2 phenotype ratio of dihybrid self crossed F1
9:3:3:1
Incomplete dominance
when the phenotype of the heterozygote is an intermediate of the phenotypes of the homozygotes
Codominance
occurs when multiple alleles exist for a given gene and more than one of them are dominant. Each dominant allele is fully dominant when with a recessive but when two dominant alleles are present, the phenotype result of the expression of both dominant alleles simultaneously
Sex Determination
in sexually differentiated species , most chromosmes exist as pairs of homolouges called autosomes, but sex is determined by a pair of sex chromosomes
locus
the location on a chromosome where a gene is located
Epistasis
occurs when one gene affects the phenotypic expression of a second gene. For example pigmentation, one gene will determine if it will or will not be seen while another determines what color will be seen.
Pleiotropy
occurs when a single gene has more than one phenotypic expression.Example the pea plant that is round or wrinkled also determines what kind of absorbtion they have. Many disease- causing genes exhibit pleiotropy
Polygenic Inheritance
the interaction of many genes to shape a single pheonotype. Leads to continuous variation
Linked genes
genes that reside on the same chromosome and thus cannot segregate independently becuase they are physically connected. Genes that are linked are normally inhereted together.
Linkage map
a chromosome map created by using the percentages of the cross over frequency. The freateer the distance between two genes on a chormosome the more places the gene can break and more likely the two genes will cross over during synapsis.
sex linked genes
genes that reside on the X or Y chromosome. Majority are X linked but Y is possible. most of these genes are phenotypically expressed in males. due to they only have one X chromosome
X-inactivation
during embryonic development in female mammals one of the two X chromosomes in each cell does not uncoil into chromatin. so X inactivation occurs and one chromosome remains coiled as a dark compact body called a Barr body
Barr body
Barr bodies are mostly inactive X chromosomes- most the genes are not expressed nor do they interact with their respective alleles.
Nondisjunction
the failure of one or more chromosome pairs or chromatids of a single chromosome to properly seperate during meiosis or mitosis
Failure for two homologus chromosomes during anaphase I or II in meiosis is
non disjuction that leads to gametes with extra or missing chromosomes
Mosaicism
During mitosis the failure of two chromatids of a single chromosome (during anaphase) to seperate and segregate produces daughter cells with extra or missing chromosomes. Occurs during embryonic development where a fraction of the body cells are efffected
Polypliody
occurs if all of the chromosomes undergo meiotic non disjunction and produce gamets with twice the number of chromosomes. common in plants
Point mutations
occur when a single nucleotide in the DNA of a gene is incorrect. can be caused by substitution, insertion or deletion.
Substitution
nucleotide is substituted for the correct one
deletion
if a nucleotide base pair is omitted
insertion
if an extra base pair is inserted
Aneuploidy
a genome with extra or missing chromosomes. Often caused by nondisjunction. Most are aneuploid gametes are sterile but some survive. examples are down syndrome and turner syndrome
Down syndrome
Trisomy 21. occurs when an egg or sperm with an extra number of 21 chromosome fuses with a normal gamete. these individuals bear various abnormalities
Turner syndrom
results when there is a nondisjunction of sex chromosomes. Sperm will either have both XY or none (O) same for eggs (XX or O). These individuals are physically abnormal and sterile
Chromosomal abberations
caused when chromosome segments are changed such as duplications, inversions or translocations
Duplications
when a chromosome segment is repeated on the same chromosome
Inversions
occur when a chromosome segments are rearranged in reverse oreintation on the same chromosome
Translocations
when a segment of a chromosome is moved to another chromosome. Example is down syndrome occuring when segment of 21 to chromosome 14. has the same phenotypic effect of trisomy 21
Nucleotides
constists of three parts, nitrogen base, sugar and phosphate
DNA
deoxyribose sugar, Nitrogen bases are adenine, thymine, guanine and cytosine and has a double helix structure
RNA
ribose sugar, nitrogen bases are adenine uracil, guanine and cytosine
mRNA
provides the instructions for assembling amino acids into the polypeptide chain, Has a liner structure
tRNA
delivers amino acids to a ribosome for their addition into a growing peptide chain. shape is clover-leafed
rRNA
combines with proteins to form ribosomes. shape is globular
DNA replication
occurs during interphase of the cell cycle and involves seperating (unzipping) the DNA molecule into two strands, each of which serves as a template to assemble a new strand. The result is two identical strands
Semiconservative replication
when each of the double stranded molecules of DNA consists of a single strand of old DNA and a new complementary strand.
helicase
an enzyme that unwinds the DNA helix during DNA replication
Replication fork
formed from the unzipping of DNA strands.
Single- strand binding protiens
used to attach to each strand of uncoiled DNA to keep them seperate.
Topoisomerases
break and rejoin the double helix, allowing the twists to unravel and preventing the formations of knots, following the helicase
anti parallel
the DNA polymerase moves in the 3’-5’ direction along each template strand. The new strand grows in the anti parallel 5’-3’ direction.
Leading strand
for the 3’-5’ template strand replication occurs continusouly as the DNA polymerase follows the replication fork, assmebling a 5’-3’ leading strand.
Okazaki segments
short segments of complementary DNA. For the 5-3’ template strand, the DNA polymerase moves away from the replication fork. this is because it can assemble nucleotides only in 3-5’ direction. so it has to make these short segments and then return back to the replication fork.
DNA ligase
what is used to connect the Okazaki segments producing a single complement strand
lagging strand
the strand that is produced from the 5’-3’ templete strand, hence its name because it takes longer to assemble than the leading strand
Primase
enzyme that begins replication with a short segment of RNA nucleotides, called the RNA Primer.
RNA Primer purpose
the leading strand and every Okazaki segment on the lagging strand must begin with an RNA primer so that DNA polymerase can attach succeding DNA nucletotides
Where does energy from elongation come from
DNA elongation energy is provided by two additional phosphates that are attached to each new nucleotide. Breaking the bonds holding the two extra phosphates provides chemical energy
telomeres
ends of eukaryotic chromosomes
telomerase
enzyme that attaches to the end of the templete strand and extends the templete strand by adding a short sequence of DNA nucleotides over and over again. This allows the elongation of the lagging strand to continue until completetion
trait
the end product of metabolic processes regulated by enzymes
protein synthesis
the process that describes how enzymes and other proteins are made from DNA
Steps of protein synthesis
transcription, RNA processing and tranlation. In transcription RNA molecules are created by using the DNA molecule as a template. After, RNA processing modifeis the RNA molecule with deletions and additions. In translation, the processed RNA molecules are used to assemble amino acids into a polypeptide.
Messenger RNA
mRNA single strand of RNA that provides the template used for sequencing amino acids into a polypeptide.
codon
a triplet group of three adjacent nucleotides on the mRNA that codes for one specific amino acid
Genetic code
provides the deconding for each codon
transfer RNA
a short RNA molecule (consisting of about 80 nucleotides) that is used for transporting amino acids to their proper place on the mRNA template
anticodon
another portion of the RNA specified by a triplet combination of nucleotides. during translation, The anticodnon of the tRNA base pairs with the codon of the mRNA
ribosomal RNA
these molecules are the building blocks of ribosomes.
Transcription
begins with initiation, elongation and ends with termination
Initiation
the RNA polymerase attaches to a promoter region on the DNA and begins to unzip the DNA into two strands. A promoter reigon for RNA transcriptions often contains the sequence TATA
Elongation
occurs as the RNA polymerase unzips the DNA and assembles RNA nucleotides using one strand of DNA as the template. Occurs in 5’-3’ direction. only one strand DNA strand is used
Termination
occurs when the RNA polymerase reaches a specail sequence of nucleotides that serve as a termination point. often contains the DNA sequence AAAAA
mRNA processing
before an mRNA leaves the nucleus it undergoes the following alterations.
1) 5’ cap is addes to the 5’ end of the mRNA
2) a poly- A tail is attached to the 3’ end of the mRNA
3) RNA splicing
4) alternative splicing
5’ cap
a gaunine nucleotide with two additional phosphate groups, forming GTP. capping provides stability to the mRNA and a point of attachment for the small sub unit of ribosome
poly-A tail
The tail consists of about 200 adenine nucleotides. it provides stability to the mRNA and also appears to control the movement of the mRNA across the nuclear envelope
RNA splicing
removes nucleotide segments from mRNA. before mRNA moves to the cytoplasm small nuclear ribonucleoproteins delete introns and splice the exons.
exons
sequences that express a code for a polypeptide
introns
intervening sequences that are non coding
alternative splicing
allows different mRNA;s to be generated fro the same RNA transcript. by selectively removing different parts of an RNA transcript, different mRNA’s can be produced.
Translation
GTP acts as an energy supplier for this event to take place.
1) Initiation begins when the small ribosomal subunit attaches to a special region near the 5’ end of the mRNA
2) Elongation begins as tRNA binds to the A site of the ribosome delivering amino acids. it then moves from the A site to the P site.
3) termination occurs when the ribosome encounters one of the three stop codons. At termination, the completed polypeptide, the last tRNA and the two ribosomal subunits are released.
Mutations
any sequence of nucleotides in a DNA molecule that does not exactly match the original DNA molecule from which it was copied.
Point mutation
a single nucleotide error and includes:
substitution, deletion, insertion or frame shift
Frameshift
mutation occurs when a nucleotide is deleted or inserted. causing all subsequent nucleotides to be displaced one position.
Silent mutation
occurs when the new codon still codes for the same amino acid
Missense mutation
occurs when the new codon codes for a new amino acid
nonsense mutation
occurs when the new codon codes for a stop codon
Mutagens
radiation or chemicals that can cause mutations
Carcinogens
are mutagens that activate uncontrolled cell growth (cancer)
Proofreading
DNA polymerase checks to make sure that each newly added nucleotide correclty base pairs with a template strand. if not it is removed and replaced correctly
Mismatch repair
enzymes repair error that escape the proof reading ability of DNA polymerase
Excision repair
enzymes remove nucletotides damaged by mutagens. the enzymes identify which of the two strands of the DNA contain a damaged nucleotide and hten use the complementrary strand as a template to repair.
Chromatin
in eukaryotes DNA is packaged with protiens and form this matrix
nucleosomes
DNA that is coiled around bundles of histone proteins to form DNA-histone complexes
Euchromatin
describes the reigons where DNA is loosely bound to nucleosomes. DNA in these regions is actively being transcribed
Heterochromatin
represents areas where the nucleosomes are more tightly compacted and where DNA is inactive. stains darker than euchromatin
transposons
jumping genes, can move to a new location on the same chromosome or to a different chromosome. They may change the expression of a gene or turn on or off its expression or have no effect
bacteriophages
viruses that only attack bacteria
Virus structure
- a nucleic acid (either RNA or DNA) contains the hereditary info. Can be double or single stranded
- capsid or protein coat encloses the nucleic acid
- envelope surrounds the capsid of some viruses. incorporating phospholipids and proteins obtained from the cell membrane of the host
capsomeres
assemble to form the capsid
Lytic cycle
a virus penetrates the cell membrane of the host and uses the enzyme of the host to produce viral nucleic acids and viral proteins. They then assmeble into new viruses and erupt from the host cell, destroying the cell in the process.
Retroviruses
are ssRNA viruses that use an enzyme called reverse transcriptase to make DNA complement of the RNA. then the DNA can be used to create another lysogenic cycle
Lysogenic
the viral DNA is temporarily incorporated into the DNA of the host cell lying dormant as a provirus or prophage. Until stimulated then goes into lytic cycle
binary fission
the chromosome replicates and the cell divides into two cells one chromosome in each .
plasmids
short circular DNA molecules outside the chromosome. carry genes that are beneficial but not normally needed for survival .
episomes
plasmids that can become incorporated into the chromosomes.
Conjugation
a process of DNA exchange between bacteria. A donor bacterium produces a tube or pilus that connect to a recipient bacterium. Through the pilus the donor sends chromosomal or plasmid DNA.
F plasmid
contains the genes that enable a baceterim to produce pili, when a recipient receives F it then can do the same. F+ and F-
R plasmids
provide bacteria with resistance against anitbodies
transduction
occurs when new DNA is introduced into the genome of a bacteria by a virus.
transformation
occurs when bacteria absorb DNA from their surroundings and incorporate it into their genome. specialized proteins on the cell membranes facilitate this
operon
in prokaryotes is a unit of DNA that controls the transcription of a gene. it contains a promoter, operator, structural gene, and regulatory gene
promoter of operon
a region that is a sequence of DNA to which the RNA polymerase attaches to begin transcription
operator of operon
region that blocks the action of RNA polymerase if this region is occupied by a repressor protein.
structural genes of operon
contain DNA sequences that code for several related enzymes that direct production of some particular end
regulatory gene
lying outside the operon region produces repressor proteins
lac operon
in E.coli contols the breakdown of lactose. induced by lactose. therefore the enzymes that it produces are inducible enzymes
trp operon
in E.coli produces enzymes for the synthesis of the amino acid tryptophan. Here tryptophan is a corepressor. these are repressible enzymes
Regulatory proteins
repressors and activators operate similarly to those in prokaryotes. influencing how readily RNA polymerase will attach to a promoter region. in many cases, numerous activators are acting in concert to influence transcription.
nucleosome packing
influences whether a section of DNA will be transcribed. DNA is tightly packed by methylation of histones, making transcription more difficult.
acetylation
addition of acetyl groups will break down histones and allow for the uncoiling and transcription of specific DNA regions
RNA interference
occurs when interfering RNAs block mRNA transcription or translation or degrade existing mRNA.
Recombinant DNA
contains DNA segments or genes from different sources. DNA transferred from one part to another.
can occur naturally through viral transduction, bacterial conjugation transposons or technology
Recombinant DNA technology
uses restriction enzymes to cut up DNA. they are very specific and cut at specific places. manufactured from bacteria that produce these enzymes to combat virus
gel electrophroesis
DNA fragments of different lengths are separated as they diffuse through a gelatinous material under the influence of an electrical field. often used to compare DNA fragments of closely related species
DNA fingerprinting
RFLPs produced from DNA is left on an object are compared to the DNA of an individuals RFLP. used in crime scenes
polymerase chain reactions
uses synthetic primers that initiate replication at a specific nucleotide sequence.
