Casari Flashcards
Is incomplete dominance a demonstration of blended inheritance? Why?
Incomplete dominance is NOT a demonstration of blended inheritance because when you obtain F1 hybrid (if you cross a snap white dragon) you can obtain all population pink. But then, when you cross again 2 F1 individuals, under the blended inheritance hypothesis, you would expect to obtain all the offspring to be pink. Differently, you obtain 25% red, 25% white and 50% pink. Thus, the two parental phenotypes re-appear (in half population). Therefore, incomplete dominance is not blended inheritance.
What is overdominance?
Overdominance is the situation where heterozygous are more fit than the two homozygous (e.g. malaria and sickle cell anemia).
Matrilinear inheritance and X-linked inheritance: how to distinguish?
Mitochondrial (mitochondrial) inheritance: always passage of the disease from mothers to all offspring, only the daughters will pass the disease to their offspring. Instead, in X-linked inheritance, also the father can pass the disease onto his offspring. There is no male-male transmission, as in all X-linked inheritance.
- Define a pure-breed parental strain
For a specific phenotype (e.g. the wrinkled pea or yellow and green pea), a parental strain is defined when it cross breeds with autohybrid (with itself), it always produces the same descendent with the same phenotype. this is not the case of F1 (if you cross two F1, you obtain opposite homozygous phenotype). While, if you cross a pure-breed homozygous parental strain, you always obtain the same phenotype and of course the same genotype.
How many cells are present in a Punnet square describing the cross of AABb x aaBb strains?
Think about which possible gametes the two individuals can give: AABb can only give 2 types of gametes = AB and Ab; aaBb can only give aB and ab. If you cross them (2x2 gametes): there are 4 cells describing the cross of AABb and aaBb.
Can co-dominant traits appear in a homozygote? Why?
No, because co-dominant means that you have to see the phenotypic expression for both alleles, and of course you should be heterozygous for this. Example is AB group. On the erythrocytes of a person who has AB blood group there are both A and B “flag”. It is co-dominant for both of them. This only occurs in heterozygote individuals.
Describe the concept of allele and trait
An allele is an isoform of a specific gene. We have two forms of alleles. The trait is phenotype, what you can see in the individual (e.g. green or yellow pea).
What is a haplotype?
A haplotype is an arrangement of alleles on the same piece of chromosome; e.g. marker 1 for allele A, marker 2 for allele B and 3 for allele C: haplotype is 123 for this specific piece of chromosome.
What is the probability for heterozygous Aa parents of having a homozygous aa son?
It resembles the F1 crosses and is 25%. Though THIS IS NOT A COMPLETE ANSWER. It asks about a son, not offspring. The probability of having a female or a boy is the same, and is 50%. Though, being these two probabilities independent from one another, you have to use the formula of relative probability: the final answer is 1/8 (1/4 x 1/2).
List the percentage of genome (genomic DNA) shared, in the proposed order, by the following couples: brother-sister, dizygotic twins, identical twins, mother-son, father-mother.
brother-sister 50%
dizygotic twins 50% DIZYGOTIC TWINS ARE JUST LIKE NORMAL BROTHERS WHO HAPPEN TO BE BORN AT THE SAME TIME.
identical twins 100% (AKA MONOZYGOTIC TWINS);
mother-son 50%
father-mother 0% UNLESS CONSAGUINOUS MATING
Describe in which case a chromosomal inversion causes a monogenic disease
In an inversion= chromosomal mutation. All the events regard a single chromosome in which there are 2 breakpoints; if one of them cuts through the middle of the gene, this piece of chromosome is inverted there will be inactivation of the single gene. If instead, the inversion occurs in an inter-genic region, not affecting any other gene, you have a monogenic disease.
Functional consequence of type 1 dynamic mutations
Type 1 dynamic mutations regard the coding region. There is expansion of mostly the CAG triplet repeat in a coding region. So, there is a stretch of glutamine enlarged in the affected individual.
The first functional consequence is GAIN OF FUNCTION GOF of the protein. Proteins with very long polyglutamine stretches become very sticky and thus you sequester TFs and other relevant molecules for the cell. The second functional consequence is mostly neurodegeneration in this kind of diseases.
Which mutations are detectable by array-CGH?
Array-CGH is a comparative technique allowing to compare the patient’s genome to a reference genome (wild type). Since it is a quantitative technique, you can only detect if there is loss or gain of genetic material, that, in terms of chromosomal mutations are, duplications or deletions of DNA. Also, when you have reciprocal translocation accompanied by loss or gain of DNA.
What is gene conversion?
When there is recombination, in the holiday model, invasion of opposite chromosome that is going to pair. During pairing of single strand to homologous opposite strand, possible formation of hybrid double strands if the site of recombination is touching for example a polymorphism or an allele. This is starting of recombination. Then 2 fates:
1. this invasion continues with the correct recombination event and form this point on there is recombination
2. after the starting of recombination, you don’t follow the isomerization and recombination, but strand goes to the original strand. In this way, you have a small piece of DNA that is hybrid: one strand being father chromosome and the other is mother chromosome. So, there is a mismatch (G and on other strand T). This mismatch can be corrected by gene repair system. If this is corrected, the T is replaced by C, re-establishing the correct alleles.
But in 50% of cases you correct the good base: the G is replaced by A, thus you have gene conversion. This is a sort of exit of tentative event of recombination.
Gene conversion happens during recombination and converts one allele into the homologous allele.
Explain the possible link between heteroplasmy and incomplete penetrance
Heteroplasmy has to do with mitochondrial genome. Since we have not only 2 copies of mitochondrial genome, but between 100 and even 1000 in some cells, we can have mixture of genome per single cells. So, sometimes frequently in mitochondrial dieseases, there is acertain threshold for expressing mitochondrial phenotype. For example, if you have 60% mutant mitochondrial genome, you have the disease phenotype. If you have 40% mutant, this is tolerated and thus you are not expressing the phenotype.
The key word is thus threshold: threshold of amount of diseased mitochondrial genome is responsible for what it seems to have incomplete penetrance at pedigree analysis. Maybe the mother (not affected) can have affected or non-affected daughters/sons depending on amount/threshold of diseased mitochondrial genome.
Heteroplasmy definition, threshold to have mitochondrial diseases.
