Q1)
In this we are asked to find either a sibling or a parent of rat A. the genetic composition of rat A should be somewhat equal to the sibling or parent but the DNA of rat A isn't identical to the others. DNA strands' nucleotide composition of organisms are characteristic to the organism.
Some of the mutations that happen such as duplication of sequence fragments and other types of mutations during gamete formation brings about diversity in the offspring. whilst some of the DNA sequences are the same as that of the parents, some other mutations bring about changes in the DNA content.
Once the DNA fragments are cut with restriction enzymes, some of the fragments obtained are same for parent and offspring and some are different. Rat D maybe a parent or sibling as some of their fragments have the same nucleotide composition, hence same molecular weight but some other fragments have different compositions.
Q2)
Rat C is an identical twin of rat A. identical twins are exceptional cases where the nucleotide compositions are the same. Identical twins come from the same fertilised egg therefore DNA sequences and mutations that happened during gamete formation is the same.
In the gel given, both these rats have DNA fragments of the same length and same nucleotide composition, hence their mobility in the gel is the same, which is why they're found at the same distance from the wells.
In this both rats have bands at the same levels, hence DNA is identical.
Q3)
crossing over during homologous recombination is to bring about genetic diversity (C).
During meiosis, in gamete formation, crossing over is where DNA fragments are exchanged between homologous chromosomes. This makes the daughter cells formed not identical to the parent cell nor the other daughter cells. Due to this phenomenon, gametes formed have different compositions to that of parent cells and other gametes.
Due to this, genetic diversity is brought about as offspring are genetically different to the parents and siblings.
Q4)
Dad 3
the child will gain his DNA from both mother and father. genotype of the child is from genes from both parents. During gel electrophoresis, we can analyse the bands obtained in the childs lane, and try to match it with the mother and father. Bands should either match mothers DNA or fathers DNA.
When we look at the bands on childs DNA, if there are bands corresponding to that level in the mothers DNA, then it has been inherited from the mother. If there are no bands of that length in the mothers DNA, it should be from the fathers, then we have to look at the possible fathers DNA and find which father has a DNA band of that length.
Since there are a lot of bands, we can match with both mothers and fathers DNA to find the father correctly.
In this case Dad 3 and mothers DNA bands together make up the childs DNA band pattern, hence he is the father.
