A human being has an estimated 30,000 genes located on 46
chromosomes (23
pairs). These genes are known, collectively, as the human genome, with a
total of about 3 billion DNA base pairs. Thus, option A is correct.
Each chromosome contains hundreds to thousands of genes, which carry
the
instructions for making proteins. Each of the estimated 30,000 genes in the human genome makes an average of three proteins. Protein-coding
sequences (specifically, coding exons) constitute less than 1.5% of the human genome. Aside from genes (exons and introns) and known regulatory
sequences
(8–20%), the human genome contains regions of noncoding DNA. More than
90 percent of the genome is noncoding DNA, sometimes called "junk" DNA, that has no known function. Therefore, option B
seems correct.
Repeated Sequences (also known as repetitive elements or repeats) are patterns of DNA or RNA that occur in multiple copies (in arrays of tandemly repeated sequence or dispersed repeats) throughout the genome. They have been recognized as a
potential source of genetic variation and regulation, with over two-thirds of a sequence consisting of repetitive elements in humans.
Thus, Option C is correct.
Chromosome 1 is the
largest human chromosome, representing approximately 8
percent of the total DNA in cells. Two copies of chromosome 1, one copy
inherited from each parent, form one of the pairs, containing around
2000 genes that provide instructions for making different proteins.
The
Y chromosome is one of the two sex chromosomes in humans (the other is the X chromosome). The Y chromosome (found in males) represents almost 2 percent of the total DNA in cells. It likely contains 60-70 genes that provide instructions for making proteins, involved in male sex determination and development. Therefore,
Option D although correct shows wrong numbers.