Exam Study Flashcards
Amorphic alleles
Also known as null alleles
Type of recessive mutation
- a non functional protein is produced or
- no protein is produced
Hypomorphic alleles
- type of recessive mutation
- a poorly functioning protein is produced
- reduced amounts of normally functioning protein is produced
Recessive mutations include
Null/amorphic alleles
And
Hypomorphic alleles
Dominant mutations include
Hypermorphic alleles
And
Neomorphic alleles
Hypermorphic alleles
- type of dominant mutation
- negative phenotypic consequences due to over production of a normal protein
- negative phenotypic consequences due to production of a protein with increased activity levels
Neomorphic alleles
- negative phenotypic consequences due to the presence of an altered protein that has a new function
- negative phenotypic consequences when altered protein interferes with the wild type protein
Incomplete dominance
All genotypes aa AA and Ab differ phenotypically
Ex. Flowers red white and heterozygous is pink
New one is an intermediate btw the phenotypes
Codominance
AA aa and Aa all differ phenotypically BUT Aa exhibits phenotypes of both homozygotes. Ex. Marble cow
Allelic series
Describes the dominance hierarchy of multiple alleles
A null allele is nonfunctional
A hypomorphic allele had partial function
ABO blood type example of codominance
Gene I encodes for the transferase enzyme
IA encodes for transferase which adds acetylgalactodamine
IB encodes for one that adds galactose
i encodes for nonfunctional one
Individuals with tupe AB blood type have both proteins
Wildtype allele
A functional enzyme or other protein is produced
Sometimes refers to the most common allele in the wild
Often dominant over loss of function allele
Loss of function allele
An enzyme or other protein is no longer being produced, is produced at lower levels or is non-functional
Haplosufficiency
Half as much protein is synthesized, yet this is enough/sufficient to achieve the wild type phenotype
Gain of function mutations
Mutant allele produces a protein that has increased detrimental function
Ex, huntingtons disease
Dominant allele can be a loss of function as well
Haploinsufficiency
In the heterozygote, half as much protein is synthesized and this is not sufficient for a normal phenotype
Ex. Tailless cats
Recessive lethal alleles
Cause death in only homozygotes
Ex. Yellow mice (effect on colour is dominant)
yy white
Yy yellow
YY death
Another ex, manx cats
mm normal tail
Mm no tail
MM lethal
Dominant lethal alleles
Can be expressed in both the heterozygotes and homozygotes
Ex. Huntingtons
BB lethal
Bb lethal
bb not lethal
Tay sachs gene is an example of
Recessive lethal genes
tsts is only lethal genotype
a+
Wild type allele
Produces functional polypeptide
= wild tupe phenotype
a
Recessive amorphic allele
loss of function
Produces a partially functional polypeptide
= severe mutant phenotype
a^h
Recessive hypomorphic loss of function allele
Produces a partially functional. Polypeptide
= a mild mutant
a^D
dominant negative allele
Produces a polypeptide that interferes with the wildtype polypeptide
= severe mutant phenotype
Penetrance
Proportion of individual organisms having a particular genotype that express the expected phenotype
- you either have it or you don’t
Expressivity
Degree of which a phenotype is expressed
Mild to severe
Variation within the individual
Piebaldism
Is an example of Expressivity
Abscence of skin melanocytes
What causes incomplete Penetrance and Expressivity
Due to effects of other genes and the environment
Environmental factors that can effect phenotypic expression
- age
- sex
- temperature
- chemicals
Norm of reaction
The range of phenotypes expressed by a single genotype under different conditions
Ex, heart attack and excercise I think
Temperature sensitive allele
Ex. In Himalayan 🐰, dark pigment only develops in low temperatures
necessary for that pigment production
Enzyme inactivated at higher temperatures so the extremeties which are colder (ears and paws) are darker in colour
Phenocopy
A change in phenotype arising from the environment that is the same as the phenotype produced by a mutation in gene
Genetic interactions
Many genes can contribute to a single phenotype due to interaction last the cellular or biochemical level
Dilute gene
Dilute effect In cat coat colour is autosomal recessive
A cat requires two copies for the colour to be diluted
DD dense pigmentation
Dd carrier of dilute gene
Dd coat colour is diluted
Complementation
Occurs when two strains of an organism with different homozygous recessive mutations that produce the same phenotype produce offspring with the wildtype phenotype when mated/crossed
It will only occur if the mutation is in different genes
The other genome supplies the wildtype allele complement to the mutant allele
Ex, deafness
Genetic epistasis
Masking of the expression of one gene by another
No new phenotypes are produced
Epi static gene does the masking
Hypo static gene is masked
Phenotypic ratio of 9:3:4 indicates
Recessive epistasis
Phenotypic ratio 12:3:1
Indicates dominant epistasis
Phenotype ratio 3:1
Complete dominance
Phenotype ratio 1:2:1
Incomplete dominance
Phenotype ratio 2:1
Recessive lethal allele
Phenotype ratio 9:7
Complementation
Pleiotropy
A single gene can be responsible for a number of distinct and seemingly unrelated phenotypic effects
Ex. Sickle cell disease can be chronic infection and/or joint pain
Cystic fibrosis can be digestion problems and mucus infections
Inbreeding depression
Inbred lines of experimental species are often less vigorous than hybrid lines
They are homologous for alleles that were present in the founding line
Heterosis
Aka hybrid vigour
When two different inbred lines are crossed, the hybrids are heterozygous for many genes
These heterozygotes display Heterosis or hybrid vigor
Hardy Weinberg principle
Used to predict genotypes through allelic frequencies in a population
P^2 + 2pq + q^2
Dosage compensation
A way of equalizing gene expression in the face of different gene dosage
Ex. Like X-inactivation
X-inactivation
Mary Lyon proposed the random inactivation of one of the female X-chromosomes
If a cell contains more that 2X chromosomes, all but one of them are inactive (Barr bodies)
Barr bodies
Inactive X chromosomes
(All but one)
Barr bodies
Inactive X chromosomes
(All but one)
Hemizygous
50% of cells will express one allele, 50% the other
Ex, females are functionally hemizygous since 50% of X express one allele and 50% express another
- ex. Calicocats are orange and brown
Colourblindness in humans
Mechanisms of genetic exchange in bacteria
Transformation
Conjugation
Transduction
Bacteriophages
Bacterial viruses
Reproduce by infecting bacterial cells
Ex. T4, lambda
Bacterial genome
Circular molecules of seven million base pairs called bacterial chromosomes
Plasmids
Small circular DNA that can replicate independently of bacterial chromosome
Ex. F+ factor
Episomes
Large, circular DNA that can integrate into the bacterial chromosomes for the replication to remain separate
Transformation
Transfer a free (out of the cell) piece of dna from one bacterium into another
Competent bacteria cells can take up dna from the environment and incorporate it into their genome
No cell contact required
Sensitive to dnase
Conjugation
Sexual rebroduction mediated by the fertility/F factor
Direct transfer of dna from one cell to another via the establishment of a cytoplasmic bridge
Ex F factor
Genes in the F factor direct synthesis of the bridge
F Pili help pull the cells together
When a bacterial cell that has undergone transformation divides, how many of its 2 new cells will be transformed
Just one will have the new dna that was transformed since outside of circle chromosome
one nontransformed cell
What did the Utube experiment do?
Established the need for bacterial contact
Two auxotrophic strains were separated by a filter that allowed mixing of the medium of bacteria
No prototrophic pacteria were produced
Concluding the genetic exchange requires direct contact btw bacterial cells
Does the whole double stranded dna enter the cell during transformation
No, just one strand enters
And pairs with bacterial dna
The other is hydrolyzed
What happens to the remainder of the dna strand fragment that is not incorporated during transformation?
It is degraded
T4 bacteriophage
Protein head
Genome contains 168 800 base pairs and 150 characterized genes
Fairly large and complex genome
Cookie Monster look like
Lytic virus
Lambda bacteriophage
Genome contains 48 502 base pairs and 50 genes
May be Lytic or lysogenic
Head has packaged dna
Tail is like long and worm like
Describe the plates with bacteria and how they look
Bacteria grow in a liquid or solid media
Eventually solid grey colour cause lawn of dense culture of bacteria
Bacteriophages produce clearings(plaques) on platess with dense bacterial cultures within hours of infection
What percent of the bacterial chromosome undergoes transformation? Why is this important?
Only 0.2-0.5%
So it is for this reason transformation can be used to determine the distance between bacterial genes
If two genes are very close, they will be present on the same piece of transforming dna
Transformation is measured by a change in phenotype and occurs only within a certain frequency
How does conjugation with f factor work
The f pill I on donor cell (with F+) make contact and pull cells together
Genes on f factor direct synthesis of the conjugation bridge
One strand of dna is cleaved at origin of replication of the f factor
Rolling circle replication transfers one strand of the f factor into the recipient cell
Replication of the f factor occurs in both cells (one strand is synthesized in each cell)
Transduction
Bacteriophages can hijack bacterial chromosome genes during the process of phage assembly
During infection, the phage can donate the hijacked genes to another cell
Transduction
Bacteriophages can hijack bacterial chromosome genes during the process of phage assembly
During infection, the phage can donate the hijacked genes to another cell
Functions of a genetic material
Must replicate
Control growth and development of the organism
Allow organism to adapt to changes in the environment
What was Griffiths experiment?
Experiment, they were two types of bacteria, give it to myself one custom to die. The other did not send the little back to you. It was heated/killed did into the most. The most lived with a heated dead little bit. It was mixed with a non-little bit here, and ejected in the mood. The most died, indicating transformation of bacterial DNA from skilled lethal to other bacteria.
What are the nucleic acids?
Adenine
Thiamine
Quiet mean
Cytosine
Uracil
What are the nucleic acids made up?
Nitrogen containing pieces
Sugar Pentose
Phosphate
Chargaffs rule
How the structure of dna was deciphered
Found that
Purines=pyrimidines
A + G = T + C
Watson crick model
Background A = T and G = C
Helical structure
Bases stuck like coins over each other
Assumptions that dna is a double helix, the two strands were anti parallel, the sugars form a phosphate backbone
The bases are held together by H bonds
Key points: DNA structure
Complementary base pairs (A with T, G with C)
Antiparallel strands
The two strands of the helix have opposite chemical polarity (5’ & 3’ ends)
Techniques for dna and rna analysis
Molecular hybridization
Gel electrophoresis
Avery MacLeod McCarty experiment
Tested to see what the chemical nature of the transforming substance was
Took three test tubes of same substance and added rnase (destroys dna), preotease (destroys proteins), dnase (destroys dna) respectively into the three test tubes. The only one that lost the function was dnase one indicating that the transforming substance is dna
How many rings are in purines vs pyrimidines
2 for purines and 1 for pyrimidines
William asturby
x ray diffraction analysis showed dna is a polymer of stacked bases
William asturby
x ray diffraction analysis showed dna is a polymer of stacked bases
Rosalind Franklin and Maurice wilkins found
Dna is a helix
How many bonds and what kind of bonds btw a and t
2 hydrogen bonds
How many bonds and what kind of bonds between c and g
3 hydrogen bonds
How many base pairs and what is the length of on turn of the dna helix
10 base pairs
3.4 nm
Polymerase chain reaction steps
- Denaturation- at high temperature (95*C) seperates the hydrogen bonds between strands, separating strands
- Primer annealing- the forward primer sticks to the bottom strand and the reverse primer to top (52*C)
- Elongation (72*C) dna polymerase enzyme works to elongate the strand
How w many copies of dna after n cycles of polymerase chain reaction
We do 2^n
Molecular hybridization
Includes a fluorophore donor and a quencher acceptor.
Can determine the location of a gene on a chromosome
You make single stranded dna probe complementary to the stand you are looking for that tags it with a fluorescent colour
You can extract the dna you’re interested in, mix the probe with the dna
But then you need to add heat to denature it, making it single stranded, so the probe can get in and bind to the gene of interest and then the fluorophore can emit a fluorescent signal, indicating the locus of the gene
How does dna become super coiled prokaryotes?
There’s a single strand nick in the dna strand and it’s rotated 360* left to lights and right to relax
How is the bacterial chromosome formed/folded
Circular unfolded (350 u)
40-50 loops (30u)
Supercoiled and folded (2u)
Human dna
Diploid
2 sets of genes, 2 sets of chromosomes
Haploid dna 3.3x10^9 nucleotides
Haploid genome: 23 chromosomes
Total length of diploid genome = 2m
Human nucleus= 5-10um
Eukaryotes have very large genomes
Their chromosomes must be extensively folded and packaged
Chromatin
Dna + histones + protein
Each eukaryotic chromosome consists of
One large linear mlc of dna
Large amounts of two types of proteins:
- 5 histones (high positive charged polypeptides)
- a divergent group of non-histone proteins
Nucleosomes
Nucleosome core
146 nucleotide pairs of dna wrapped as 1.65 turns around octamer of histones
11 nm thick
Linker dna
Between the nucleosomes, 8-114 nucleotide pairs in length
Nucleosome core
Consists of 2 mlc of each of four histones
The complete Nucleosome contains histone 1
30nm chromatin fiber
The second level of dna packaging
Third layer of dna packaging
Inter-phase chromosomes
Chromosome scaffold
300nm wide compressed to 250nm
Width of a chromosome
1400 nm
Prototroph
Bacterial cells capable of growing in minimal medium and synthesizing all of the essential mlc required for bacteria growth and reproduction
Prototroph
Bacterial cells capable of growing in minimal medium and synthesizing all of the essential mlc required for bacteria growth and reproduction
Nucleotides are always added to the
C-3 of the pentose sugar
Compound chromosome
Formed by the fusion of homologous chromosomes, sister chromatids or homologous chromosome segments
Reciprocal translocation
Pieces of two non-homologous chromosomes are exchanged without any net loss of genetic material
Translocations
Occur when a segment from one chromosome is detached and reattached to a different (nonhomologous) chromosome
Pericentric inversion
Segments are flipped
Ex. Chimpanzees and humans have same genes on chromosome 4 except segment is inverted
Formation of an inversion loop
One homologous chromosome has an inverted segment, so the chromosomes form an inversion loop to align the alleles and chromosomes properly
