Although the exact number of genes in human dna is unknown, scientists estimate the number to be around 20,000 to 25,000.
only one answer
which of the following is true about these genes?
a.)each human has completely different genes and alleles.
b.)there is only one variation, or allele, of each gene.
c.)there are several variations, or alleles, of many genes.
d.)each human has the exact same combination of alleles.

Describe the change in phase and temperature as water moves from the oceans to the atmosphere and then returns to earth again as rain. a) evaporation : temperature increases; condensation : temperature decreases; precipitation (rain) : temperature decreases b) evaporation : temperature increases; condensation : temperature decreases; precipitation (rain) : temperature increases c) evaporation : temperature decreases; condensation : temperature decreases; precipitation (rain) : temperature decreases d) evaporation : temperature increases; condensation : temperature increases; precipitation (rain) : temperature decreases