Answer:
C) Through genomic imprinting, methylation regulates expression of the paternal copy of the gene in the brain.
Explanation:
The pattern of gene expression wherein either paternal or maternal gene is expressed in specific cells while the other one is prevented from expression is known as genomic imprinting.
In the given example, the maternal copy of the gene on chromosome 15 is expressed in brain cells while its paternal copy is not expressed in these cells. Hence, the pattern of expression of this gene is regulated through genome imprinting. One of the mechanism is methylation of cytidine residues of CpG islands of the DNA that are more frequently present within promoters of the genes.
When the cytidine residues of these sequences are methylated into 5-methylcytidine, the transcription factors do not bind to these promoters preventing the expression of these genes.
Hence, methylation of cytidine residue in CpG islands of the promoters of the gene present on chromosome 15 could have silenced its expression in brain cells.
Answer and Explanation:
Cyclins and cyclin-dependent protein kinases (CDPKs, cell proteins) also function to control the cell cycle. A group of cyclins: the G1 cyclins, are synthesized during G1 phase and function to activate CDPKs which initiate DNA synthesis at the G1/S checkpoint. The cell fails to progress to S phase if there is no sufficient synthesis of G1 cyclins. After a cell passes through this point, the G1 cyclins are degraded, allowing for another group of cyclins: the M cyclins (mitotic cyclins) to be synthesized. M cyclins activate a second group of CDPKs which allow the cell to pass the G2/M control point and into mitosis.
In the G1/s check point, entrance into the S phase is blocked if the genome is damaged. In the G2/M check point, entrance into the M phase is halted if the DNA replication is incomplete. In the M phase, anaphase blocked if chromatids are not properly assembled.
Methane has a higher potent than co2 I believe