Because dark hair is represented by a pair of dominant alleles.
Allele genes are segments of DNA (deoxyribonucleic acid) made up of pairs. One is from the mother (egg) and the other from the father (sperm), which are found at the same locus on homologous chromosomes. They are classified into:Recessive Allele genes: represented by lowercase letters (aa, bb, vv) where the phenotypes are expressed only in homozygosis Dominant Allele Genes: represented by capital letters (AA, BB, VV) and expressed phenotypically in heterozygosis.
The dominant genes are those that determine an inherited trait even when in a simple dose in the genotype. That is, they determine their character even in the absence of another dominant allele. In short, when the offspring receives at least one dominant allele, they will express that trait. In the case of the question above, black hair is a characteristic represented by the dominant allele, if all the offspring expressed this characteristic it is because everyone has at least one copy of that allele.
relative humidity, temperature and dew point -- are bound together in the mathematical relationship below. relative humidity changes when temperatures change. because warm air can hold more water vapor than cool air, relative humidity falls when the temperature rises if no moisture is added to the air. so i would say a
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