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Transcript
Intro…GENETICS MENDEL & MEIOSIS MENDEL’S LAWS OF HEREDITY I. WHY MENDEL SUCCEEDED Gregor Mendel – father of genetics 1st studies of heredity – the passing of characteristics to offspring Genetics – study of heredity The characteristics passed on called traits 1. MENDEL CHOSE HIS SUBJECT CAREFULLY Used garden peas for a model organism Have male & female gametes (sex cells) Male & female same flower Know what pollination & fertilization mean He could control the fertilization process Not many traits to keep track of 2. MENDEL WAS A CAREFUL RESEARCHER USED CAREFULLY CONTROLLED EXPERIMENTS STUDIED ONE TRAIT AT A TIME KEPT DETAILED DATA II. MENDEL’S MONOHYBRID CROSSES MENDEL STUDIED 7 TRAITS CAREFULLY seed shape/color, flower color/position, pod color/shape, plant height Mendel crossed plants w/ diff. traits to see what traits the offspring would have These offspring are called hybrids – offspring of parents w/ different traits A monohybrid cross is one that looks at only one trait (let’s look at plant height – tall or short) A. THE 1ST GENERATION Mendel crossed two plants – 1 tall & 1 short These plants are called the parental generation (P generation) The offspring were all called the 1st filial generation (F1 generation) All the offspring were tall B. THE 2ND GENERATION Next, Mendel crossed two plants from the F1 generation The offspring from this cross are called the 2nd filial generation (F2 GENERATION) Mendel found that ¾ of the offspring were tall & ¼ were short (the short plants reappeared!!!!!!) VOCABULARY: Allele Genotype Phenotype Dominant Recessive Trait Heterozygous Homozygous Laws: Independent Assortment Segregation TO GO ANY FURTHER, WE MUST UNDERSTAND ALLELES, DOMINANCE, & SEGREGATION Genes – a section of DNA that codes for one protein These genes are what control & produce traits The genes Mendel studied came in two forms (tall/short - round/wrinkled yellow/green…….etc.) Alternate forms of a gene are called alleles Alleles are represented by a one or two letter symbol (e.g. T for tall, t for short) ALLELES CONT’D THESE 2 ALLELS ARE NOW KNOWN TO BE FOUND ON COPIES OF CHROMOSOMES – ONE FROM EACH PARENT THE RULE OF DOMINANCE A dominant trait is the trait that will always be expressed if at least one dominant allele is present The dominant allele is always represented by a capital letter A recessive trait will only be expressed if both alleles are recessive Recessive traits are represented by a lower case letter DOMINANCE CONT’D LET’S USE TALL & SHORT PEA PLANTS FOR AN EXAMPLE WHICH OF THESE WILL SHOW THE DOMINANT & RECESSIVE TRAIT? TT Tt DOMINANT TRAIT tt RECESSIVE TRAIT THE LAW OF SEGREGATION MENDEL ASKED HIMSELF……..”HOW DID THE RECESSIVE SHORT PLANTS REAPPEAR IN THE F2 GENERATION?” HE CONCLUDED THAT EACH TALL PLANT FROM THE F1 GENERATION CARRIED TWO ALLELES, 1 DOMINANT TALL ALLELE & ONE RECESSIVE SHORT ALLELE SO ALL WERE Tt SEGREGATION CONT’D HE ALSO CONCLUDED THAT ONLY ONE ALLELE FROM EACH PARENT WENT TO EACH OFFSPRING HIS CORRECT HYPOTHESIS WAS THAT SOMEHOW DURING FERTILIZATION, THE ALLELES SEPARATED (SEGREGATED) & COMBINED WITH ANOTHER ALLELE FROM THE OTHER PARENT The law of segregation states that during gamete formation, the alleles separate to different gametes F1 GENERATION TT FATHER MOTHER Tt T t Tt tt F2 GENERATION - the law of dominance explained the heredity of the offspring of the f1 generation - the law of segregation explained the heredity of the f2 generation PUNNETT SQUARE CROSS T T X Tt CONT’D TT X Tt T T T T T T T t T t T t PHENOTYPES & GENOTYPES PHENOTYPE – The Physical appearance – how an organism looks – the Trait GENOTYPE – the Allele combination…Aa or AA or aa…….also Ttyy or ttyy or TTYY HOMOZYGOUS – 2 ALLELES SAME HETEROZYGOUS – 2 ALLELES DIFFERENT Like Homo-Sexual… Same gender couple Hetero-Sexual Different gender couple ANSWER ON YOUR SHEET TRAITS = BLUE SKIN & YELLOW SKIN BB – IS THIS HOMOZYGOUS OR HETEROZYGOUS? HOMOZYGOUS IS BLUE SKIN OR YELLOW SKIN DOMINANT? BLUE MENDEL’S DIHYBRID CROSSES MONOHYBRID – MENDEL LOOKED AT ONE TRAIT IN HIS DIHYBRID CROSSES – HE LOOKED AT 2 TRAITS WANTED TO SEE IF TRAITS ARE INHERITED TOGETHER OR INDEPENDENTLY DIHYBRID CROSS TOOK TWO TRUE BREEDING PLANTS FOR 2 DIFFERENT TRAITS (ROUND/WRINKLED SEEDS ------- YELLOW/GREEN SEEDS) 1ST GENERATION WHAT WOULD HAPPEN IF HE CROSSED JUST TRUE BREEDING ROUND W/ TRUE BREEDING WRINKLED (ROUND IS DOMINANT) ALL THE OFFSPRING ARE ROUND DIHYBRID CROSS – 1ST GENERATION CONT’D SO WHAT DO YOU THINK HAPPENED WHEN HE CROSSED TRUE BREEDING ROUND/YELLOW SEEDS WITH TRUE BREEDING WRINKLED/GREEN SEEDS ALL THE F1 WERE ROUND AND YELLOW DIHYBRID CROSS – 2ND GENERATION TOOK THE F1 PLANTS AND BRED THEM TOGETHER (PHENOTYPE WAS ROUND/YELLOW X ROUND/YELLOW) 2ND GENERATION FOUND ROUND/YELLOW FOUND ROUND/GREEN FOUND WRINKLED/YELLOW FOUND WRINKLED/GREEN ( 9 : 3 : 3 : 1 RATIO) -9 -3 -3 -1 EXPLANATION OF 2ND GENERATION MENDEL CAME UP W/ 2ND LAW – THE LAW OF INDEPENDENT ASSORTMENT Genes for different traits (Pea color, and flower color) are inherited independently of each other Just because you have brown hair, doesn’t mean you will be short! DIHYBRID CROSSES A LITTLE DIFFERENT HhGg X HhGg What are the possible Allele combinations? USE THE FOIL METHOD First, Outer, Inner, Last FOIL – FIRST, OUTSIDE, INSIDE, LAST H hGg X HhGg 1. HG 2. Hg 3. hG 4. hg BOTH PARENTS ARE THE SAME NOW LET’S DO A DIHYBRID CROSS HhGg X HhGg HG Hg hG HG HHGG HHGg HhGG HhGg Hg HHGg HHgg HhGg Hhgg hG HhGG HhGg hhGG hhGg hg HhGg Hhgg hhGg hhgg hg WHAT ARE THE PHENOTYPIC RATIO’S? HhGg X HhGg DD: 9 HhGg Dr: 3 HhGg Hhgg rD: 3 HhGg hhGG hhGg rr: 1 Hhgg hhGg hhgg HG Hg hG HG HHGG HHGg HhGG Hg HHGg HHgg hG HhGG hg HhGg hg PROBABILITY Does real life follow Punnett Squares?? NO!!!!!! – only shows what will PROBABLY occur Like flipping a coin 10 times: PROBABILITY says you’ll get heads 50% of the time. But you may not … try it. Certainly over time, with hundreds and hundreds of flips, YES, you’ll end up with 50% heads