Lesson 4 section 5.1-5.2 Inheritance and Genetic crosses A Brief History In the past, people did not understand how traits were inherited, but there were many guesses based on things that could be observed. Two theories emerged…. Blending Theory - offspring are a straight mix Particulate Theory traits are inherited as "particles", offspring receive a "piece" Golden Doodle Who was Gregor Mendel? He was known as the “FATHER OF GENETICS” He discovered how traits were inherited GENETICS – study of heredity HEREDITY – the passing of traits from parents to offspring Mendel’s Peas Mendel did his study on pea plants which have many traits tall/short purple /white flowers round/wrinkled seed Traits in Pea Plants Pea plants can be self-fertilized or cross-fertilized True-Breeding Plants -always create plants that look like themselves Hybrids – offspring of true-breeding plants HYBRIDS Some traits are dominant over others. Tall x Short = all tall offspring (hybrids) *Tall is the dominant trait T * Short is recessive t Mendel discovered that each trait is controlled by two factors (alleles) Genes – factors that determine your traits Genes are located on chromosomes Quick Check - What do we know so far? 1. The “Father of Genetics” is ____________ 2. Genetics is the study of _____________, which is how traits are passed from _________ to ____________ 3. Mendel studied what organism? ____________ 4. If one trait covers up another one, we say that it is ______________, the one that is covered up is ______ 5. A “true-breeding” plant is one that can only produce plants like itself a) true b) false Mendel’s Experiments Draw the crosses GENOTYPE - what genes, letters, the organism has (TT, Tt, tt) TT x tt PHENOTYPE - what it looks like (tall or short) Tt x Tt TT Tt Tt tt Check for understanding 1. The passing of traits from parents to offspring is known as _____ 2. Who was the father of genetics? _________ 3. Genes are located on _______________ 4. Every gene is made of two a. genotypes b. alleles c. cells 5. The organism’s outward appearance, such as wrinkled seeds are referred to as the a) phenotype b) genotype 6. The letters (ex. RR) that represent the traits are referred to as the a) phenotype b) genotype 7. An organism that has two different alleles, or letters, such as Rr is: a) homozygous b) heterozygous 8. 7. An organism that has two of the same alleles, or letters, such as RR is: a) homozygous b) heterozygous 9. Which of the following sets would represent Mendel’s Parent (P) generation? a) RR x RR b) Rr x Rr c) RR x rr 10. When two different alleles occur together, such as R r, the one that is expressed is a) dominant b) recessive 11. What is the diagram shown below called? What does this letter actually represent? Check for understanding 1. A one-eyed purple people eater is crossed with a two eyed purple people eater. All of their offspring have two eyes. Which trait is dominant? 2. If you use the letter E for this gene. What is the genotype of the offspring if the parents were EE x ee EE = two eyes Ee = two eyes ee = one eye 3. If you crossed the offspring with each other? How many of the new offspring would you expect to have two eyes? Mendel’s Principles Dominance and Recessiveness Some alleles can cover up or hide the other. The one that is expressed is DOMINANT. PRINCIPLE OF SEGREGATION When a parent makes sperm or eggs, their genes separate. The GAMETES (egg or sperm) contain only one of the pair. PRINCIPLE OF INDEPENDENT ASSORTMENT Each trait is inherited independent of other traits. Each gamete can inherit any combination of genes Possible: GB Gb gB gb Mendel crossed plants with two separate traits to see the outcome. Consider this cross: Yellow, round seeded plant YYRR x yyrr What is the phenotype of the offspring? What is the genotype? x Green, wrinkled seeded plant What if the offspring RrYy self fertilize? YyRr x YyRr Use “FOIL” to determine the gametes created by each parent: What if the offspring RrYy self fertilize? YyRr x YyRr YR Set up a 4x4 Punnett Square. YR Fill out the offspring by combining letters (keep the R’s and Y’s together) Yr yR yr Yr yR yr What if the offspring RrYy self fertilize? YyRr x YyRr YR Set up a 4x4 Punnett Square. YR Fill out the offspring by combining letters (keep the R’s and Y’s together) Yr yR yr Yr yR yr YyRr x YyRr What if the offspring RrYy self fertilize? YR Count the number for each phenotype Yellow, round? ______ Yellow, wrinkled? _____ YR Yr yR Green, round? ____ Green, wrinkled? _____ yr Yr yR yr DIHYBRID CROSSES - involve 2 traits, heterozygotes The ratio is always: 9 3 3 1 Try this cross: A yellow, round seeded dihybrid (YyRr) crossed with a green seeded, wrinkled (yyrr) YR yr yr How many? Yellow, round? ______ Yellow, wrinkled? _____ Green, round? ____ Green, wrinkled? ____ yr yr Yr yR yr Beyond Mendel - experiments after Mendel showed there were other types of INHERITANCE PATTERNS Some genes did seem to “blend” together... Codominance → both traits are expressed in the heterozygotes Show the cross of a red cow and a roan cow: RR = Red Cow RW = Roan Cow (heterozygote) WW = White cow Show the cross of a roan cow (RW) and a white cow (WW) A white flower is crossed with a red flower. All of the offspring are pink. RR = red RW = pink WW = white This is called INCOMPLETE DOMINANCE Show the cross of two pink flowers: Multiple Allele Traits - more than two alleles control the trait Example: Blood Type Blood Type Genotype A AA, AO B BB, BO AB AB (codominant) O OO (recessive) Show the cross between: AB x O AO x BO O x O POLYGENIC TRAITS - when many genes control one trait, usually resulting a wide RANGE of phenotypes Examples: Skin color, height, eye color (human) Sometimes a set of alleles can cover up another set. Check out the coat color in labradors. What’s going on here?