I have a bad habit of chewing on my finger nails
RrXtXt×RrXTY is representing the cross between the white eyed female and red eyed male.
Option D
<h3><u>Explanation:</u></h3>
The genes that are discussed here both are completely dominant over their recessive alleles. In the autosome, the dominant R gene is responsible for red eye and recessive r gene is responsible for sepia eye. But in allosome, the dominant T gene allows the eye colour to be expressed and the recessive t gene doesn't allow eye colour to be expressed and makes it white.
As the female do have 2 X chromosomes and the female is white eyed, then both the chromosomes of female have t gene.
As the male is red eyed and have one X chromosome, so the male must have atleast one R gene in autosome to make the eye colour red and must have T gene in his X chromosome to make it appear in phenotype.
So the most possible cross that is given here is RrXtXt×RrXTY.
The excretory system allows animals to remove metabolic waste their bodies. Many of these substances are potentially toxic. in Mammals nitrogenous toxins like urea are expelled through liquid urine while in reptiles and birds the nitrogenous compounds are expelled as a solid. This allows birds and reptiles to use less water in the processes of metabolism.
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.