Heredity – Unit 2 lesson 4 What is Heredity? Heredity is when traits are passed from parents to offspring Gregor Mendel Born in Austria, 1822 Entered a monastery at 21. Monks taught him science. Working in the monastery garden, he discovered the principles of heredity The Mystery of Pea Plants • Mendel was curious why pea plants had different traits (stem length, seed color, etc.) • Pea plants were a good choice to experiment with because they grow quickly and there are many different characteristics • Pea plants can also self pollinate (they have male and female sex cells) and parent traits can be controlled. Characteristics and Traits * A characteristic is a feature that has different forms in a population (hair color, height) * A trait is the different form of a characteristic (blond, black or brown hair, or tall or short height) Mendel Used the Scientific Method * Ask a question – How are traits inherited? * Form a hypothesis – It is passed from parent to offspring * Test the hypothesis – Breed plants and offspring * Analyze the results – There are patterns * Conclusion – Traits are inherited in predictable patterns * Communicate results – Publish results First Generation Experiment * He used pea plants to study 7 different characteristics * He crossed (bred) a plant with purple flowers with a Plant with white flowers. All the offspring had purple flowers. * What happened to the trait for white flowers? Dominant and Recessive Traits * Mendel found that one trait was always present and one disappeared. * He called the trait that showed the dominant trait. * The trait that disappeared or was covered was called the recessive trait. Second Generation * The purple offspring self pollinated and the recessive trait reappeared. * For every 3 plants with purple flowers, there was 1 with white flowers. * This pattern appeared for all 7 traits tested. Discovering Mendel * It was only 30 years after Mendel died that his work got the attention and value it deserved. He is known at the “Father of Genetics.” Where do traits come from? * Genes – carry instructions for an inherited trait * Different forms of a gene for a trait (dominant or recessive) are called alleles * The dominant allele is shown with a capital letter. * The recessive allele is shown with a lower case letter. Check your understanding! Purple flower color in peas is dominant over white flowers. Which of the following pairs of alleles would give purple flowers? A. PP B. Pp C. pp D. Both PP and Pp Check your understanding! Which of the following pairs of alleles would give white flowers? A. PP B. Pp C. pp D. Both PP and Pp Genes The genotype is the genetic makeup of an organism. It is the combination of alleles for a specific trait (the combination of letters). The phenotype is the appearance of the trait or what you see. There can be any number of alleles for a gene, but an individual can only have two alleles (one on each homologous chromosome) Check your understanding A, B and O are the ________________ of the human blood type ______________ A. genes, gene B. genes, allele C. alleles, gene D. alleles, allele Genotypes If the two alleles are the same ( two recessive bb or two dominant BB), we same the genotype is homozygous. If the alleles are different, (Bb) we call the genotype heterozygous. Check your understanding Which of the following is a homozygous genotype? A. AA B. Aa C. aa D. Both AA and aa Punnett Squares A Punnett square is uses to organize all the possible combinations of offspring from a particular parent. Each square has one of each parents’ alleles Each box shows the probability of a particular phenotype and genotype in the offspring. Try this! Tongue rolling is a dominant trait. You only need one allele. See if you can roll your tongue. See if your parents and siblings can roll their tongues. Now figure out your genotype (homozygous dominant, homozygous recessive or heterozygous.) Not so simple dominance Co-dominance – Each allele has equal dominance. For example, in blood type, A and B types are equally dominant. So if you have the alleles AB, then you are AB type. O is recessive to both, so you can have the alleles AA and AO and be type A for blood type. Incomplete dominance – Neither allele is dominant so both alleles create a new phenotype. For example, in some flowers the red color allele (R) and the white color allele (W )produce pink flowers Genes and Traits Sometimes, one gene influences more than one trait. Some traits, like eye color, are the result of several genes working together. Remember, the environment also plays a role. You may have genes to be tall, but if you do not eat a healthy diet, you may not reach your full potential height