Heredity b b B b Bb Bb bb bb When organisms reproduce, genetic information from each parent is passed from one generation to the next. This passing of traits from parents to offspring is called heredity. Human heredity is quite interesting. Many traits that are easily seen are inherited, like hair and eye color, skin type, and height. Traits for health conditions can also be inherited. Examples of such conditions include hemophilia (a blood-clotting disorder) and color-blindness (a disorder that makes a person unable to distinguish some colors). Traits like height, weight, and the shape of your body are inherited, but are also greatly influenced by your environment. For example, your diet and the amount of exercise you get are a couple of things that can change your body size and appearance. The genes you inherit give you the potential for many traits, but the person you become depends on your environment as well. Genetics is the study of heredity. Gregor Mendel is the scientist who is known as the “Father of Genetics.” Mendel did many early experiments with heredity. Every organism has a set of genes that determine traits. These genes occur in pairs because every person gets one gene for a certain trait from their mom and one from their dad. Each gene in a pair is called an allele. People do not get more genes/traits from mom or from dad, just some of the genes in a pair are dominant and some are recessive. If one of the alleles (genes in a pair) masks the effect of another allele, it is called a dominant allele. The allele that is masked by the dominant allele is called a recessive allele. Alleles are often written using letters. A dominant allele is shown with a capital letter, such as “B” for brown eyes. The recessive allele for the same trait is shown with a lowercase version of the same letter. So, in this case, “b” would stand for lighter eyes. The possible set of alleles for an organism is known as the genotype. The actual appearance the trait takes on is called the phenotype. Therefore, the genotype for a person with brown eyes might be “BB”, and the phenotype would be “brown eyes”. Due to the fact that offspring inherit one allele from each parent. Sometimes an organism will inherit two dominant alleles or two recessive alleles for a trait. So if a person had the gene pair “BB” he/she would have brown eyes, and if the person had the gene pair “bb” the person would have lighter eyes. When the person has two of the same alleles for a trait they are said to be homozygous for that trait. However, sometimes the offspring will inherit one dominant trait and one recessive trait. In this case, the dominant trait would “mask” or “override” the recessive trait. So, if a person had the gene pair “Bb” he/she would have brown eyes. When the person has two different alleles for a trait they are said to be heterozygous for that trait. A table called a Punnett Square can be used to predict the possible traits that offspring will have based on the traits their parents have. In a Punnett Square, the top of the table shows the alleles contributed by the male. The side of the table shows the two alleles contributed by the female. It is sometimes difficult to predict exact traits, like hair and eye color, because there are so many variations in the genes that control these traits. But, a Punnett square will still give a good idea of what traits the offspring might show. See example Punnett Square below to see how it works: Gene from mom Gene from dad Pair of chromosomes alleles b b Mrs. Alligood has the genotype “Bb” for eye color, she got these alleles from her parents. She has brown eyes. Mr. Alligood has the genotype “bb” for eye color, he got these alleles from his parents. He has light eyes. Look at the Punnett Square to the right to see the possibility of eye color for their daughter. B Bb Bb b bb bb

1. Use the “Heredity” article to help you determine the best answer to the heredity question below. You must read the article carefully. Baby Mice Seif’s pet mouse had babies. Five of the babies were black and two were white. The father mouse was black. The mother mouse was white. Seif and his friends wondered why the mice were different colors. These were their ideas: Jerome: Baby mice inherit more traits from their fathers than their mothers. Alexa: The baby mice got half their traits from their father and half from their mother. June: Male traits are stronger than female traits. Seif: Black mice have more traits than white mice. Fiona: The black baby mice are probably male and the white baby mice are probably female. Lydia: Parent’s traits like fur color don’t matter. Nature decides what something will look like. Billy: Blood type determines what traits babies will have. Which friend do you most agree with and why? Explain your thinking, you will try this twice. Try #1 (before reading): Try #2 (after reading): CORRECT ANSWER (from Teacher): 2. Highlight the ALL of the BOLD vocabulary words and their definitions in the “Heredity” article. Then, write the definitions for the words below. Try to put them in your own words. Allele: Dominant: Recessive: Genotype: Phenotype: Homozygous: Heterozygous: Punnett Square: