You and your genes (1)

Gap-fill exercise

Fill in all the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!

The instructions for how an organism develops are found in the of its cells. Genes are for a cell that describe how to make .
Genes are sections of very long DNA that make up chromosomes in the nuclei of cells. DNA has a double structure. Both strands of the helix are made up of different , which always pair up in the same way. The of bases in a gene is the code for building up amino acids in the correct order to make a particular .
Sex cells have only one copy of each . The chromosomes in a pair have the same genes in the same place. There are different versions of genes, called . A person may have two different alleles of any gene.
Each characteristic is determined by a single gene. There are dominant and alleles. Girls and boys may be similar to their parents and inherit characteristics of either the father or mother. This depends on the combination of maternal and paternal alleles in the fertilised . The inheritance of gender is related to the presence of the X and sex chromosomes.