Gregor Menel The father of genetics 1822-1864 Menel: Unerstaning Inheritance What is Genetics? GENETICS - is the science of how traits are inherite. In other wors, how traits pass from parent to offspring. What are TRAITS? TRAITS are characteristics (the way we look, are, or think). For example, eing tall or short, lon or ark-haire, rown eyes or lue eyes, light or ark skinne, funny or serious, etc Traits are genetic an are passe own from parent to offspring. Have you ever wonere WHY you inherit certain traits from your parents? Why o you have freckles, or ark hair, or lue eyes, or curly hair, or imples, etc? Gregor Menel aske lots of questions aout inheritance Who was Gregor Menel? Gregor Menel was an Austrian monk, who live in the 1800 s. Menel conucte thousans of experiments on pea plants to see how traits (shape, color) were passe from generation to generation. Menel is known as the Father of Genetics for figuring out the asic rules of how traits are inherite. What type of experiments i Menel o? Menel crosse pea plants with ifferent traits (eg. tall & short). He starte with PURERED plants (showe same trait for many generations short parents ha short offspring) He crosse a tall parent with a short parent to see what the offspring plants woul look like. The 1 st generation of offspring were ALL tall! The short trait was lost it ha isappeare. What happene? In the 2 n generation, the lost short trait reappeare in ¼ of the offspring. (Even though neither parent was short!) Menel teste MANY traits an foun that one form of the trait was always ominant in the first generation of offspring, ut that the hien trait re-appeare in 25% of the secon generation. So, what are Menel s rules of inheritance? Menel figure out that: Traits are controlle y PAIRS of factors (genes) that are inherite from your parents (one from mom, one from a). Some factors are ominant - they mask or hie the other factor. (For example, the tallness gene hies the shortness gene in pea plants.) 1
Let s get the new vocaulary straight GENES - are the factors that control an inherite trait. ALLELES are the ifferent forms of a gene. (the TALL an SHORT alleles are the 2 forms of the HEIGHT gene in pea plants) *We inherit one allele (or form of a gene) from our mom an one allele from our a, so we have 2 alleles for every gene. Let s get the new vocaulary straight DOMINANT ALLELE - is one whose trait always shows up when the allele is present. It can mask or hie the other form of the trait. It is shown with an upper-case letter, for example T. Example: Tall stems = or Let s get the new vocaulary straight RECESSIVE ALLELE is one whose trait is hien whenever the ominant allele is present. It will only show up if OTH alleles are recessive. It is shown with a lower-case letter, for example t. Example: Short stems = tt Let s get the new vocaulary straight HOMOZYGOUS - Organisms with 2 same alleles. tt Let s review When you cross the tall an the short plant, the offspring get a Tall allele (T) from the tall plant an a short allele (t) from the short plant. In the first generation, the ominant TALL allele hies the recessive SHORT allele, so ALL the offspring are tall. They are all heterozygous. What happens if heterozygous plants cross? In the SECOND generation, the heterozygous plants cross an it s possile to have an offspring with the 2 recessive alleles. With 2 recessive alleles, the plant will e SHORT, not tall. tt HETEROZYGOUS - Organisms with 2 ifferent alleles. tt tt SUMMARY When stuying genetics, we nee to take 2 things into account: PHENOTYPE - an organism s PHYSICAL appearance. (3 plants are tall, 1 is short) GENOTYPE an organism s GENETIC makeup (alleles). (1 plant is, 2 plants are, an 1 plant is tt) tt Proaility & Hereity: Punnett Squares How can we figure out which traits will e inherite? To talk aout inheritance, we nee to use our new vocaulary We ve learne aout ominant & recessive alleles: Dominant alleles are more powerful, an can hie a recessive trait. Shown with an upper-case letter ( T for tall stems) Recessive alleles can e hien when a ominant allele is present. Shown with a lower-case letter ( t for short stems) 2
How can we figure out which traits will e inherite? You know the ifferences etween genotype an phenotype: Genotype escries which genes (alleles) are present.» = 2 ominant alleles» = 1 ominant & 1 recessive» tt = 2 recessive alleles Phenotype escries what the physical trait looks like.» Tall stems ( an )» Short stems (tt) More vocaulary Geneticist use 2 terms to escrie GENOTYPE: Homozygous the organism has 2 same alleles.» = 2 ominant alleles» tt = 2 recessive alleles Heterozygous the organism has 2 ifferent alleles.» = 1 ominant & 1 recessive allele So, how o we know which genotype or phenotype the offspring will e? We can use a tool calle a punnett square to preict how likely it is for an offspring to inherit certain traits. A PUNNE SQUARE: is a chart that shows ALL the possile cominations of a genetic cross. shows genotype an phenotype of the offspring. is also use to preict the proaility (the chance) that an offspring will have a certain trait. How o we raw a Punnett Square? R is ominant for Roun sees. r is recessive for wrinkle sees. oth parents are heterozygous an have roun sees. The two-letter cominations are the possile genotypes of the offspring. They are RR,,, an rr genotypes. From this it is possile to etermine the proaility (chance) that a see will have: a roun see phenotype (3/4 or 75%) OR a wrinkle see phenotype (1/4 or 25%) 3
Cross a homozygous guinea pig with lack fur () with a homozygous guinea pig with white fur (). (lack fur is ominant over white fur). Cross a homozygous guinea pig with lack fur () with a homozygous guinea pig with white fur (). Cross a homozygous guinea pig with lack fur () with a homozygous guinea pig with white fur (). Cross a homozygous guinea pig with lack fur () with a homozygous guinea pig with white fur (). The result? All 4 possile offspring will e heterozygous an have one ominant allele for lack fur an 1 recessive allele for white fur. All the guinea pigs will have the lack fur phenotype; an genotype. More practice prolems 1) Cross a heterozygous tall pea plant () with a homozygous short pea plant (tt). Tall stems (T) are ominant over short stems (t). What are the possile offspring from this cross? 2) Cross a rait who is heterozygous for short ears (Ee) with another rait who is heterozygous for short ears (Ee). Short ears (E) are ominant over long, floppy ears (e). What are the possile offspring from this cross? Review - #8 from HW Tall eyealls (T) are ominant over short eyealls (t). Mr. Kras is homozygous for tall eyealls. What is his genotype? T T Mrs. Kras is heterozygous (). Does she have tall eyealls or short eyealls? Tall eyealls (the short allele is hien). Review - #8 from HW Draw the punnett square for Mr. an Mrs. Kras. T t T T Any ay that Mr. an Mrs. Kras woul have tall eyes (100% chance), ecause they get a ominant TALL eyeall allele from Mr. Kras. While 50% of their kis might have the short eyeall gene from their mom, it is ALWAYS hien if the ominant (T) gene is present! Punnett Square Practice Prolems Dalmatians are often orn eaf. These ogs are eaf if they inherit two copies of the recessive allele for hearing (). 4
Punnett Square Practice Prolems A og reeer has a male og that she woul like to ree. The og can hear, so she knows his genotype is either DD or. Punnett Square Practice Prolems She will only ree the og if his genotype is DD, so there will e no risk of eafness in the puppies. Punnett Square Practice Prolems To test his genotype, she rees him to a eaf () female. Use Punnett squares to preict the outcomes if the male is DD or. D D If the male is homozygous ominant (DD), all puppies will e ale to hear. The recessive eaf allele is hien. Punnett Square Practice Prolems To test his genotype, she rees him to a eaf () female. Use Punnett squares to preict the outcomes if the male is DD or. If the male is heterozygous (), D half of the puppies will e orn eaf. They will e homozygous for the recessive eaf allele. Punnett Square Practice Prolems Jimmy Neutron an Ciny Vortex may preten not to like each other, ut they en up marrying later in life! Punnett Square Practice Prolems Ciny wants to know if their chilren will all have ig, poofy hair ( or ), the ominant trait in Retroville. Jimmy an Ciny are oth heterozygous for the ig hair trait. What are Jimmy an Ciny s genotypes? Jimmy = Ciny = Punnett Square Practice Prolems Ciny, who is prou of her ig hair, oes not want a flathaire chil (). Set up a Punnett square to figure out whether Ciny will e isappointe or not. rain last! 25% of our kis will have flat hair. Sorry Ciny! Challenge Question! In purple people-eaters, 2-horns is ominant (H), an no horns is recessive (h). Two purple people-eaters crosse an they ha 4 chilren shown elow. (What are the genotypes?) Work ackwars from a punnett square to fin out the genotypes an phenotypes of the parents. hh hh Challenge Question! What are the genotypes an phenotypes of the parents? Genotype =, hh Phenotype = One parent ha horns, the other parent ha no horns! h? h?? H? h hh hh hh hh 5
Incomplete Dominance With some traits, there is a situation where the What ominant you think allele will is not happen completely in this ominant. cross? When RR (re the flowers) organism x is rr heterozygous, (white flowers) the trait is expresse as a len. All offspring will e heterozygous ut NOT re (ecause it is not completely ominant). R R They will e a len of re an white PINK! r r Incomplete Dominance What if we cross 2 of the pink flowers? (pink flowers) x ( pink flowers) R r R RR r rr 1 (RR) has RED flowers. 2 are a len () PINK flowers. 1 (rr) has white flowers. Exit Slip In humans, rown eyes () are ominant over lue (). A man who is heterozygous for rown eyes marries a lue-eye woman an they have 3 kis. 1) What is the genotype of the father? 2) What is the genotype of the mother? 3) Draw a punnett square for this cross. 4) What are the possile phenotypes an genotypes of their chilren? 5) What is the proaility (% chance) that their chil will have lue eyes? rown eyes? What is a peigree chart? How is it use? One important tool a geneticist uses to trace the inheritance of traits is a peigree chart. A peigree chart is one that geneticists use to track an inherite trait through several generations of a family to try to unerstan how it is inherite. How o you rea a peigree chart? A CIRCLE represents a FEMALE. A SQUARE represents a MALE. A horizontal line represents marriage. A vertical line an rackets connects parents to chilren. How o you rea a peigree chart? A shape that is not shae inicates that the person oes NOT have the trait. A shape that is half-shae inicates that the person is a carrier (has 1 allele). A shape that is completely-shae inicates that the person has the trait (homozygous oth alleles for the trait). What oes this peigree chart show? How many people are unaffecte carriers? How many people are affecte y the isorer? How many carriers are female? If only 1 parent is a carrier, what is the proaility of having a chil with the isorer? 6
What oes this peigree chart show? How many people are unaffecte carriers? How many people are affecte y the isorer? Can we tell if the isorer is ominant or recessive? If 1 parent has the isorer, what is the proaility of having a chil with the isorer? 7