Children tend to resemble their parents in many ways; they may have like eye color, hair texture, height, or skin tone. this is because children inherit genes from both parents. a child receives 1/2 of his/her genes from the mother and the other half from the father. genes are part of our dna; our dna makes up the chromosomes in our body and sex cells.

sex cells or gametes are produced during the process of meiosis. gametes have 1/2 the number of chromosomes as do regular body cells, like skin or muscle cells. when fertilization takes place, the two sets of alleles from the male gamete (sperm) and the female gamete (egg) are combined.

many years ago, gregor mendel discovered that we have dominant and recessive traits that are determined by our genes. for examples, brown eyes are dominant over blue eyes. scientists represent the gene for a trait with a letter: capital letter for dominant and lower case letter for recessive. a brown-eye person would have the genotype bb or bb. a blue-eyes person would have the genotype bb. whenever a dominant trait is combined with a recessive trait (bb), the dominant trait most often masked the recessive trait.

look at the grid above. this is called a punnett square. it shows the genotypes of two parents and then the possible gametes that could be produced by each parent. we use the punnett square to show the possible combinations of genes and the resulting traits. in this case, two black rats mate and their potential off-spring could be black (bb, bb) or white (bb). the chances of having a black rat in this example is 3: 4 or 75% and having a white rat is 1: 4 or 25%.

drag the labels to the correct locations within the punnett square.

black

dominant gene

phenotype

recessive gene

white