A color-blind (X-linked recessive) human with Klinefelter syndrome has parents both of whom have normal color vision. 4a. From which parent did he receive his extra X chromosome? Explain

The extra X chromosome is received from mother.

Klinefelter's syndrome is the condition of chromosomal aberration where the person has an extra X chromosome. This means the genotype of the person is 44+XXY and the total chromosome number is 47. This condition is achieved due to inappropriate meiotic division and one of the sperm or ovum has the an extra X chromosome.

Here both the parents are normal in terms of colour vision. So the father cannot have the gene of colour blindness because if it was present, then father would have been colour blind because he has only one X chromosome per cell. So its present in mother who is heterozygous in terms of colour blind gene. So the extra X chromosome also came from her which made the presence of two defective X chromosomes in the offspring and made it colour blind.

step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.

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