There are some questions from a genetic\'s study guide that I need a little help

Question

There are some questions from a genetic's study guide that I need a little help understanding in simpler matter:

1) How can RNA splicing make different proteins from a single primary transcript?

2) How can mutation of a non-protein coding region of the genome affect a trait?

3) What is the difference between cis- and trans-regulatory elements?

4) What's one way in which meiosis creates genetic variation in eukaryotes?

I've found the textbook answers, but I'm having trouble understanding those questions.

Explanation / Answer

1. There is a process called alternative splicing. This usually occurs in eukaryotes. Splicing involves the removal of introns and joining of introns. This is the basal mechanism. But in alternative splicing, some exons may also be removed from the gene. This leads to varying combinations of the different exons in the gene. These varying combinations give us different proteins.

2. A mutation of a non-protein coding region can affect a trait if the region codes for a cis regulatory element. These are regions which regulate nearby genes. In addition, deletions or an insertion or a frameshift mutation can shift the reading frame shifts to give a totally different sequence. This can affect a trait.

3. The trans-regulatory elements are those which code for transcription factors. these transcription factors are responsible for the process of regulation. These transcription factors can also bind to regulatory element which is next to the regulated gene. Hence, distant genes can be regulated. In cis regulatory elements, these are regions of non coding DNA which regulate the transcription of nearby genes. These usually act as binding sites for transcription factors. They are usually present next to the gene they regulate.

4. The most important way in which meiosis creates genetic variation in eukaryotes is that it creates new variants. In mitosis, the cell is just duplicated. In meiosis, due to the process of crossing over between chromosomes, variation occurs. In the process of crossing over between chromosomes from mother and father, a piece of chromosome is exchanged. This results in the new variations or recombinants seen in eukaryotes.

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