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Transcript
UNIT 7: MENDELIAN GENETICS Union Academy Charter School Traits Your characteristics: Can be PHYSICAL – how your body LOOKS eye color & hair color Can be PHYSIOLOGICAL – how your body WORKS cystic fibrosis, sickle cell anemia, diabetes Alleles G Different forms of a gene g R Different DNA sequences Alleles for eye color Blue, brown, green, hazel, etc. S s t T Think of the word OPTIONS!! Alleles are represented by letters (ex. B,b). alleles of a gene at a gene locus Alleles For each trait, you get one allele (letter) from Mom and one allele from Dad. These alleles can be represented by capital or lowercase letters. Capital letters are dominant – winner! Lowercase letters are recessive – loser! Dominant The allele that SHOWS Written with a CAPITAL letter In pea plants, tall is DOMINANT over short T = Tall t = Short Recessive The allele that is HIDDEN unless you get it from BOTH parents (bb). Written with a lowercase letter Blue eye allele = b Homozygous vs. Heterozygous Homo means SAME When both alleles are the SAME Homozygous dominant - TT Homozygous recessive – tt Aka “pure bred” Hetero means DIFFERENT When both alleles are DIFFERENT Heterozygous Aka “hybrid” – Tt Out of the three, which two look the same and why? Phenotype PHenotype – PHysical features Use descriptive words ONLY!! Tall, short, yellow, green, etc. TT = tall tt = short Tt = tall Genotype G g R Genetic make-up for a trait ‘Type-o-Genes’ To figure out genotype, ask 2 questions: Homozygous or Heterozygous? Dominant or Recessive? TT – Homozygous Dominant Tt – Heterozygous tt – Homozygous Recessive S s t T alleles of a gene at a gene locus Genotype determines phenotype Who discovered all of this? Gregor Mendel is the “Father of Genetics.” Austrian monk – grew pea plants in the garden. Studied traits like height, color, seed shape etc. Used mathematical probability to calculate results. Mendel’s laws Proposed 3 principles/laws: Principle of dominance – some traits are dominant over others. Law of segregation – each parent donates half of the genotype, chromosomes segregate independently. Law of independent assortment – alleles segregate independently (crossing over). If genes are very close together on chromosomes they are considered linked. Punnett Square A tool used to PREDICT offspring outcome Shows the cross between two parents If a heterozygous tall plant is crossed with a short plant (Tall is dominant), what kind of offspring would be possible? Tt x t t tt T t Tt Tt Genotype Phenotype tt 2/4 Heterozygous 2/4 Tall tt 2/4 Hom Recessive 2/4 Short Punnett Square T T T TT TT t Tt Tt The letters on the OUTSIDE of the Punnett Square represent the SPERM and EGG of the parents P generation The letters on the INSIDE of the Punnett Square represent the OFFSPRING (Babies) F1 generation Practice Problem In rabbits Brown fur is dominant to White fur. What would the offspring be when a Homozygous brown rabbit mates with a white rabbit? B = brown BB x B b = white bb B Genotype b Bb Bb b Bb Bb 4/4 Heterozygous Phenotype 4/4 Brown Practice Problem In Pea plants, tall plants are dominant over short plants. What would the offspring be if two hybrid pea plants pollinated? Practice Problem In rose bushes, straight thorns are dominant over curved thorns. If a homozygous dominant straight-thorned rose bush pollinates a homozygous recessive curved-thorned rose bush what kind of thorns would their offspring have? Practice Problem In rabbits, brown fur is dominant to white fur. If two brown rabbits mate and have offspring with white hair, what do we know about both parents? Show the Punnett square to prove your answer. Practice Problem In beagles, white snouts are recessive to brown snouts. What would the offspring look like if a white snout beagle mates with a hybrid brown snout beagle? Non-Mendelian genetics Mendel’s knowledge only went so far – there were exceptions that he did not study. Incomplete dominance – mixing of traits in a heterozygote (red + white = pink). Codominance – both traits are expressed (black + white = black and white spots). Multiple alleles – some traits have more than two options (blood type). Incomplete dominance - mix Heterozygotes are a mix of two traits. Ex. Wavy hair is a mix of straight and curly. Ex. Brachydactyly (short digits) – mix of digit or no digit. Ex. Pink flowers are a mix of red and white. Ex. Grey rabbits are a mix of black and white rabbits. Not represented as capital and lowercase! Ex. R = red and W = white Practice a Punnett square! RR X WW RR RW WW RW X RW Codominance – both expressed Both traits are expressed in a heterozygote. Ex. Red flower + white flower = flower with red and white pattern. Ex. Black rabbit + white rabbit = white & black spots Not represented as capital and lowercase! Codominance – the roan cow A roan cow is a classic codominance example Roan = red and white spots What color will the offspring be if you cross two roan cows? (R = red, W = white) Multiple alleles – more than 2 options Some traits have more than 2 alleles One example is blood type. The A and B represent antigens (carb/proteins that decorate blood cells). B A A B Blood type A B AB O Genotype(s) AA (IAIA) AO (IAi) BB (IBIB) BO (IBi) AB (IAIB) OO (ii) Can donate to: A, AB B, AB AB A, B, AB, O Can receive from A, O B, O A, B, AB, O O Blood type practice problem Cross a heterozygous Type A female with a Type O male. What are all the possible blood types of the offspring? Parent 1 – IAi , Parent 2 – ii IA i i IAi ii i IAi ii Polygenic inheritance Polygenic inheritance: one trait can be affected by multiple genes. Results Skin in a bell curve of results. color, height, weight etc.