Gene gains And Losses

Question 1

What is a homolog?

Answer 1

Related by decent by common ancestor

Question 2

What is an ortholog?

Answer 2

Different species (frog a, chick a, mouse a) SAME GENE - SAME FUNCTION

Question 3

What is a paralog?

Answer 3

Homolgs that evolves to have DIFFERENT FUNCTIONS. Eg: mouse a, mouse b.

Question 4

When does gene duplication take place?

Answer 4

Takes place in EARLY GENE

Question 5

How do genes become duplicated?

Answer 5

1. Unequal crossing over during meiosis (2 copies of genes here)
2. Unequal crossing over between sister chromatids - after DNA replication
3. Unequal crossing over DURING DNA replication

Unequal crossing over can happen during meiosis OR mitosis

Question 6

What is a good example of a problem that arises in humans if there is unequal crossing over?

Answer 6

Unequal crossing over can result in duplication or deletion of 22q11 in kids.

Alu repeats (pieces of the same sequence can lead to duplication and deletion).

Recombination between 277bp direct Alu repeats thought to lead to cause 22q11 microdeletion and duplication syndromes in kids.

Deletion - heart defects, developmental delays
Duplication has no symptoms - 3 genes (2 from 1 parent and 1 from the other) - heart defects and developmental delays etc.

Question 7

What are the 2 ways to GAIN a new GENE?

Answer 7

1. Unequal crossing over (this can cause duplication or deletion)
2. Retrotransposition (creating “retrogenes”)

Question 8

How does retrotransposition (creating retrogenes) work?

Answer 8

Mature mRNA is mistakenly REVERSE TRANSCRIBED BY REVERSE TRANSCRIPTASE into a cDNA and randomly inserted into the genome. The parental gene resides in a different chromosome now.

Question 9

What is the fate of duplicated genes? What happens to them?

Answer 9

1. Maintain the same function
2. Loss of function (2nd copy gets mutated and destroyed - pseudogenes - thousands of these dead genes in our genome.
3. Divergence of function (both genes become necessary) .