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DNA and genetic inheritance Typeit
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DNA is the polymer that stores genetic material in organisms. DNA strands are made up of repeating units, and the backbones consist of alternating sugar and sections. There are four possible nucleotides, depending on which is used; A, T, G and .
Body cells contain the entire human in pairs of chromosomes. These are divided into which code for sequences of , the building blocks of proteins. Some genes have alternative versions called .
We can predict the outcomes of single gene crosses using Punnett squares if we know the genotypes of the parents, i.e. whether they are homozygous (have two identical alleles) or (have two different alleles) for a trait. For example, cystic fibrosis is a condition that is only caused by inheriting two alleles. However, most characteristics are a result of genes interacting so it is not easy to predict an offspring's phenotype.
There are pairs of chromosomes that control characteristics in humans, and the final pair determines the sex of an individual. In females, the smallest pair of chromosomes will be XX, whereas in males it will be .