Term
| What is the significance of homologous recombination in the development process of an organism following fertilization? |
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Definition
| It generates genetic diversity. |
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Term
| In meiosis, following DNA replication, how many cell divisions are required to produce 4 haploid gametes? |
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Definition
| 2 divisions (1 of the chromosomes, 1 of the chromatids) |
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Term
Fill in the blanks:
Each diploid cell that enters meiosis produces (1) haploid cells, whereas each diploid cell that divides by mitosis produces (2) diploid cells. |
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Definition
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Term
| The haploid germ cell contains two types of genetic material. If one is intact parent chromosomes, then what is the other type in a normal cell? |
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Definition
| Newly created recombinants as a result of "crossing over" segments of DNA. |
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Term
| When does crossing over occur? Why does it occur at this stage? |
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Definition
| It occurs during meiosis I because the chromosomes are close together, juxtaposed against each other on the metaphase plate. |
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Term
| What occurs in homologous recombination? |
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Definition
| A genetic exchange takes place between a pair of homologous DNA sequences that are usually located on two copies of the same chromosome. |
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Term
| True or False: homologous recombination can only occur between two copies of the same chromosome. |
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Definition
| False - it can occur with any two types of DNA molecules that share the same nucleotide sequence. |
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Term
| If accidents occur during every round of DNA replication that interrupt the replication fork, what mechanism would be capable of fixing this? |
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Definition
| General (homologous) recombination |
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Term
| True or False: homologous recombination is also common in unicellular organisms. |
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Definition
| True - it has great evolutionary benefit in the reassortment of genes. |
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Term
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Definition
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Term
| What event initiates the process of homologous recombination? |
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Definition
| A double-stranded break in the DNA. |
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Term
| What process occurs in recombination following a double-stranded break in the DNA? |
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Definition
| Degradation from exposed 3' and 5' ends, allowing the "sticky" 3' ends to invade the DNA helix and pair with homologous strands. |
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Term
| When sticky 3' ends invade the homologous sequence of a DNA helix, what is formed? |
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Definition
| A joint molecule between a maternal and paternal chromosome. |
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Term
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Definition
| D-loop, since the invading (green) chromosome has "displaced" the homologous (red) DNA. |
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Term
| In recombination, what method is used to resolve the Holliday junction formed by invasion of sticky DNA? What are the two results of this method? |
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Definition
| Strand cutting is used to resolve this, either by allowing crossing-over or DNA repair (you end up with the same chromosomes you started with). |
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Term
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Definition
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Term
| True or False: The Holliday junction is rigid and will not twist or contort. |
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Definition
| False - the Holliday junction's flexibility is part of the reason that it is possible to resolve it into either two new chromosomes or the same starting chromosomes. |
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Term
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Definition
| A single allele within a chromosome is changed, rather than a large chunk, leading to a small mutation that may be allowed to survive. |
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Term
| How can one recognize that gene conversion has occurred? |
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Definition
| If three copies of one allele are present instead of two (i.e., 3 maternal copies and 1 paternal copy of a given allele) then gene conversion has occurred. |
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Term
| Does gene conversion typically change all of a gene, or only part of a gene? |
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Definition
| Only part of a gene is typically changed. |
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Term
| Does gene conversion occur more commonly in meiosis or mitosis? |
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Definition
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Term
| What two processes MUST occur in gene conversion? |
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Definition
1) A homologous recombination event that juxtaposes two homologous DNA double helices and...
2) A limited amount of localized DNA synthesis to create an extra copy of one allele. |
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Term
| What is the result of site-specific recombination in a cell? |
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Definition
| It can alter gene order and add new information to the genome. |
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Term
| What process moves mobile genetic elements between nonhomologous sites within a genome? |
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Definition
| Site-specific recombination |
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Term
| What are the three types of mobile genetic elements? |
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Definition
| DNA sequences, retroviral-like retrotransposons, and nonretroviral retrotransposons. |
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Term
| The MRSA case was an example of what type of mobile genetic element? |
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Definition
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Term
| What type of viruses are considered mobile genetic elements? Why? |
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Definition
| Retroviruses - they use transposition mechanisms to integrate their genomes into that of the host cell. They use reverse transcriptase to convert their RNA genome into DNA, which then attacks target DNA in the host via integrase and invades the host genome. |
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Term
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Definition
| Human Endogenous Retroviruses, or retroviral-like transposons, a type of mobile genetic element. |
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Term
| What was the significance of the case study on malignant melanoma? |
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Definition
| There is growing evidence to implicate human endogenous retroviruses (HERVs) in human diseases. |
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Term
| What is an L1 or LINE element? |
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Definition
| LINEs, long interspersed nuclear elements, are nonretroviral retrotransposons. Mutated copies of this make up about 45% of the human genome, though only about 50 of these copies are still able to move. |
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Term
| What type of translocation has been linked to hemophilia A? |
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Definition
| L1 insertion into the gene for blood clotting factor (Factor VIII). |
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Term
| How do nonretroviral retrotransposons move in the cell? |
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Definition
| They use a complex of endonuclease and reverse transcriptase. |
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Term
| What is the Alu element an example of? |
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Definition
| SINEs, shorter DNA repeats that lack genes for endonuclease or reverse transcriptase yet are thought to use similar mechanisms for replication to LINEs. |
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Term
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Definition
| A segment of DNA that can move from one position in the genome to another. |
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Term
| What does Alu do to the genome? How does it accomplish this? |
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Definition
| Alu is a bacterial restriction enzyme that cuts DNA in distinct patterns called Alu elements, which insert into and disrupt the function of human genes as SINE fragments, causing disease. |
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