Genetics Flashcards
Test cross
crossing the unknown genotype with a recessive homozygous
Linked genes
Does it assort independently?
What is the recombination frequency?
Genes that are closely related to one another and located on the same chromosome.
Do not assort independently
Have recombination frequency less than 50% (genes on different chromosomes have recombination frequency of 50%)
Does linked genes obey the law of independent assortment?
Linked genes do not obey the laws of independent assortment.
What is the percentage of recombinant frequency for a weakly linked genes?
50% - what would be expected of independent assortment
Recombinant frequency when genes are completely, tightly linked
0%
The range is from 0 - 50% (completely linked to weakly linked)
What determines the degree of genetic linkage?
directly proportional to the distance between the genes. The further apart the genes are, the more likely it is that there will be a recombination event between them.
Where are the linked genes located?
Linked genes are located on the same chromosome
Recombinant frequencies, and map unit
1 map unit = 1%
ex. 25 map unit - 25% of the gametes formed will have the recombinant gene
Based on distance* on the same chromosome
Incomplete dominance
Heterozygote is a mix between the dominant and recessive phenotypes. The self-cross of F1 progency shows a 1:2:1 ration (red:pink:white), different from the monohybrid cross of 3:1.
Codominance
Two dominant alleles are expressed simultaneously. Example, AB blood type
Penetrance
Number of individuals in the population who actually have the alleles that express the genotype. All or nothing.
Expressivity
Varying degree of expression of the genotype - a range.
Hemizygous
When a male has a mutation in the X gene
Aneuploidy
Abberation is the chromosome number as a result of nondisjunction
In chromosomal breakage, what is the difference between translation and duplication?
If the chromosome that breaks off joins a homologous chromosome, it is duplication. If it joins another chromosome, it is translocation
What happens to most aneuploid cells
Most aneuploid cells die
What does true breeding mean?
Homozygote genotype, when self-pollinated it will always produce the same phenotype.
What is the independent law of assortment
Dihybrid cross. The hereditary factors (genes) for color and shape assort independently of another. The segregation of one gene pair is independent of other gene pairs during the formation of the gametes. The independent assortment of the genes will occur if they are located on different chromosomes or are far apart on the same gene (far apart that they will recombine). Genes that are quite close to one another should not assort independently.
If the genes are on different chromosomes, they will assort independently because the chromosomes themselves assort independently. However, if two genes are on the same chromosome, then they may assort independently if crossing-over occurs between them.
How to find recombination frequency
The total number of progeny observed to have cross-over events between the two genetic markers divided by the total number of progeny observed
What does it mean when the genes producing tryptophan work in an epistatic fashion? Does epistasis work for an allelic pair?
production of one gene depends on the product of another gene for it to work. This doesn’t work between an allelic pair but between different genes.
What is pleiotropy
One allele has more than one effect on the phenotype. Example, a mouse with a yellow coat or a mouse that is dead with two copies of this gene
How many histones wrap DNA around themselves to form an organizational structure known as the nucleosomes?
8 histones wrapped around with DNA to form nucleosomes
The interaction between histones and DNA
Histones are composed of basic amino acids that give them a positive charge at a normal pH. DNA is negatively charged to DNA is able to wrap around 8 histones to form a nucleosome
What is the wrapped coil of the nucleosomes called?
Solenoids
What does solenoids wrap into to form?
Solenois wrap into supercoils
What is the composition of chromatin?
1/3 DNA, 2/3 protein, and little RNA
What part of the chromatin can be read?
Uncoiled part of the chromatin called the euchromatin
What part of chromatin cannot be read?
Heterochromatin
What are permanently, tightly coiled chromatin called?
Constitute heterochromatin
What is a difference between chromatin and chromosome?
Chromatin condenses during cell division to form chromosome. Chromatin is unpaired and becomes paired during prophase, becoming chromosomes.
Chromosome implies that it can be seen under the microscope.
Chromatin is the basic structural unit of a chromosome
Are sister chromatids identical?
YES
Is a single copy DNA transcribed frequently?
YES
Are repetitive DNA’s transcribed frequently?
NO
Repetitive DNA’s consist of non-coding regions of DNA that have multiple consecutive copies of the same nucleotide sequence and remains tightly coiled in regions of heterochromatin
What is the effect of DNA methylation?
DNA becomes more tightly wound and less frequently transcribed
What are the sections of RNA that do not code for proteins called?
non-coding RNA
What is the function of non-coding RNA?
non-coding RNA contribute to the regulation of the chemical changes that affect chromatin structure
Where is DNA methylated for regulation?
DNA is methylated at cytosine nucleotides
Can patterns of DNA methylation be inherited?
YES
What is it called when a chromosome posses a partner that codes for the same traits as itself?
A homologue
Humans possess how many homologous pairs of chromosomes?
23
What are the different forms of the same genes called?
Alleles
Any cell that contains homologous pairs of chromosome is called?
Diploid
Any cell that does not contain homologues is said to be?
Haploid
What phase are most cells reside in?
Non-growing G0 phase
In which cell cycle are most proteins produced? And why?
In non-growing Go phase when the cell is not exerting energy in self-replication
What is the beginning of transcription called?
Initiation
During initiation of transcription, what proteins identify a promoter?
DNA binding proteins called transcription factors
Does transcription require a promoter?
YES
What is a promoter?
A sequence of DNA nucleotides that designates a beginning point for transcription
At the promoter, transcription factors assemble into what? And what does this assembly mainly include?
A transcription initiation complex which includes the major enzyme of transcription
What is the enzyme of transcription called?
RNA polymerase
How can a promoter on a gene serve a regulatory function?
By variations causing the RNA polymerase to bind less tightly or more tightly leading to variation in transcription frequency.
What is the most commonly found promoter nucleotide sequence recognized by the RNA polymerase called?
The consensus sequence
Is there a proofreading mechanism that corrects for the errors in the transcription process? Why is this so?
NOPE because the errors made in transcription are not passed down to progeny. So the errors in individual instances of transcription are not generally harmful.
What is the end of transcription called?
Termination
When does termination of transcription occur?
When the RNA polymerase encounters a specific nucleotide sequence known as the termination sequence.
In termination of transcription, what special protein can be involved to help dissociate the RNA polymerase from the DNA template?
Rho protein
What process is the main level of activation or deactivation of genes?
Transcription
How do regulation of gene expression occur at the level of transcription?
Via proteins called activators and repressors
How are activators and repressors in transcription regulated?
The activators and repressors in DNA transcription are regulated allosterically by involving small molecules like cAMP
In eukaryotic transcription, what are the genes and proteins that interact to regulate transcription called?
Enhancers
Do prokaryotes have enhancers?
NOPE, eukaryotes only
What are enhancers?
Short, non-coding regions of DNA found in eukaryotes that function similarly to activators but act at much greater distance from the promoter. Main form of transcription regulation in eukaryotes.
What is an operon?
Multiple genes that are transcribed at once in one-go in prokarotes
In lac operon, what conditions allow it to be activated?
Low glucose
Lactose present
In lac operon, when there is low glucose, what proteins are produced in high concentration? And what is the function of this protein?
cAMP
cAMP exerts a positive control, binding to a CAP. CAP activates the promoter, forming an initiation complex for transcription
How is negative control exerted in a lac operon?
When lactose is present, it binds to the repressor protein, preventing it from binding on the operator.
When does gene repression occur in a lac operon?
When lactose is present as a source of energy
What is the function of 5’cap?
Attachment site in protein synthesis during translation and as a protection against degradation by enzymes that cleave nucleotides called exonucleases
What are exonucleases
Enzymes that degrade nucleotides
What is the function of Poly-A-tail?
Long series of adenine nucleotides also protect from exonucleases
The portions of transcripts removed during splicing
Introns
What generally longer? Introns or exons?
Introns are longer
Do Introns code for proteins?
NOPE
What is a ribozyme?
Is ribozyme a protein?
an RNA molecule capable of catalyzing specific chemical reactions. Ribozyme is not a protein.
Where does splicing occur in a cell?
In the nucleus before the final mRNA product exits the nucleus
How does alternative splicing allow the cell to incorporate different coding sequences?
Omitting certain exons, incorporating certain introns, and utilizing variable splicing sites
Sequences that contain introns are associated with what compared to sequences that lack introns
Associated with amplified protein production compared to sequences that lack introns
What are the was genes are varied in transcription?
Splicing - omitting exon, including an intron, splicing variably.
Alternative promoter sites
Terminating transcription at different sites
What is the significance of spatial segregation of transcription and translation?
Spatial segregation allows the RNA transcript to be modified before it leaves the nucleus and before translation can begin. The lack of spatial separation means that prokaryotes can carry out transcription and translation concurrently and that they do not modify RNA transcripts prior to the start of translation.
Explain why there must be combination of 3 nucleotides to produce one amino acid
Since there are 4 nucleotides - A, G, T, C
4^2 = 16
4^3 = 64.
There are 20 essential amino acids. There must be at least 3 nucleotides to make a codon for this to happen.
What does it mean when the genetic code is degenerate?
It means that there are more than one series of three nucleotides that may code for the same amino acid.
The first two pairs must be strictly complementary the last pair may not have to be
What is the code for start codons and stop codons?
Start codon is AUG
Stop codons are UGA, UAG, UAA
What is the anticodon of tRNA?
end of tRNA that complementarily matches the mRNA being translated
What is the flexbility of the last pair called in translation?
wobble pair
Eukaryotic ribosomes are made of what sediment coefficients?
40S + 60S making up 80S
What is the initiation complex in translation?
First the small subunit minds, and the tRNA containing methioine settles at the P site. This signals the large subunit to join and form the initiation complex
What signals the large subunit ribosome to join in translation?
Attachment of tRNA with methionine at the P-site signals the large subunit to join
What happens when the stop codons bind to the A site in translation?
It causes release factors to bind to the A site, which causes a water molecule to bind to the polypeptide and release it from the ribosome
What is the fate of proteins injected into the ER lumen?
Proteins injected into the ER lumen becomes membrane proteins of golgi, lysosome, ER, or other parts of the cell, or secreted outside the cell
Where does DNA replication begin?
What’s the difference between eukaryotes and prokaryotes in initiation of DNA replication?
DNA replication begins at the origin of replication in the middle of the chromosome, not towards the ends.
There is only one origin of replication in prokarotes while there are multiple origins for eukaryotes.
Difference in initiation between transcription and replication
Transcription - Promoter (also a point in gene regulation) is a spot on the DNA that tells the RNA polymerase where to begin transcription.
Replication - Starts at multiple origins of replication and requires a primer which is a short sequence of RNA that jump starts the replication.
Is DNA replication accurate?
YES. It’s so accurate that there is a mistake every billion or trillion nucleotides.
How is it that DNA replication is very accurate?
DNA polymerase also has an exnuclease function which removes incorrect nucleotide from the strand
What is the split in anaphase called?
Disjunction
What is the difference between spontaneous and induced mutation?
Spontaneous mutation is naturally occurring whereas induced mutations are caused by mutagens (environment)
What is a missense mutation?
Base substitution resulting in change of a codon, change of one amino acid
Difference between transversion and transition mutation
Transversion - purine for purine
Transition - purine for pyrimidine
Aneuploidy
Having abnormal number of chromosomes in a cell
Polyploidy
Having more than two-paired sets of chromosomes
What is the mechanism by which a somatic cell can alter its genetic makeup without meiosis?
Transposons
What are transposons?
What is it flanked by?
How many genes can transposons contain?
Can transposons copy itself? Can the copy move?
Transposons, jumping genes, can excise themselves out from a chromosome and reinsert themselves at another location.
Transposons can contain an number of genes
Transposons are flanked by identical nucleotide sequence, part of which make up the transposon
Excise and move, copy then move, copy then move the copy
What does it mean when the genes are said to be linked?
It means the genes are close to each other and tend to cross over together during genetic recombination
What does spermatogenesis and oogenesis start with?
They both start with DNA replication
What process has primary spermatocytes and oocytes have just undergone?
DNA replication, to be diploid “with sister chromatids”. They were diploids without sister chromatids before DNA replication just like regular replication (G1, S, G2 phases)
Difference between spermatids and spermatozoa
Spermatids have no tail and have more cytoplasm. Spermatozoa have tails but lost the cytoplasm.
At what meiotic stage are the primary oocytes remain in until puberty?
The primary oocyte remains in prophse I until you get your period. .
At what meiotic stage are the secondary oocytes remain before the sperm penetrates the egg?
The secondary oocyte remains in metaphse II and never completes meiosis II until fertilization
