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Intro…GENETICS

Intro…GENETICS. MENDEL & MEIOSIS. MENDEL’S LAWS OF HEREDITY. I. WHY MENDEL SUCCEEDED Gregor Mendel – father of genetics 1 st studies of heredity – the passing of characteristics to offspring Genetics – study of heredity The characteristics passed on called traits.

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Intro…GENETICS

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  1. Intro…GENETICS MENDEL & MEIOSIS

  2. 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

  3. 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

  4. 2. MENDEL WAS A CAREFUL RESEARCHER • USED CAREFULLY CONTROLLED EXPERIMENTS • STUDIED ONE TRAIT AT A TIME • KEPT DETAILED DATA

  5. 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)

  6. 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

  7. 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!!!!!!)

  8. Laws: Independent Assortment Segregation VOCABULARY: Allele Genotype Phenotype Dominant Recessive Trait Heterozygous Homozygous

  9. 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)

  10. ALLELES CONT’D • THESE 2 ALLELS ARE NOW KNOWN TO BE FOUND ON COPIES OF CHROMOSOMES – ONE FROM EACH PARENT

  11. 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

  12. DOMINANCE CONT’D • LET’S USE TALL & SHORT PEA PLANTS FOR AN EXAMPLE • WHICH OF THESE WILL SHOW THE DOMINANT & RECESSIVE TRAIT? TT Tt tt DOMINANT TRAIT RECESSIVE TRAIT

  13. 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

  14. 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

  15. FATHER MOTHER F1 GENERATION T t T t tt 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

  16. PUNNETT SQUARE CROSS T T X Tt

  17. CONT’D T T X T t T T T T T T T t T t T t

  18. 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… Hetero-Sexual • Same gender couple Different gender couple

  19. ANSWER ON YOUR SHEET TRAITS = BLUE SKIN & YELLOW SKIN BB – IS THIS HOMOZYGOUS OR HETEROZYGOUS? IS BLUE SKIN OR YELLOW SKIN DOMINANT? HOMOZYGOUS BLUE

  20. 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

  21. 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

  22. 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

  23. DIHYBRID CROSS – 2ND GENERATION • TOOK THE F1 PLANTS AND BRED THEM TOGETHER (PHENOTYPE WAS ROUND/YELLOW X ROUND/YELLOW) • 2ND GENERATION • FOUND ROUND/YELLOW - 9 • FOUND ROUND/GREEN - 3 • FOUND WRINKLED/YELLOW - 3 • FOUND WRINKLED/GREEN - 1 ( 9 : 3 : 3 : 1 RATIO)

  24. 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!

  25. DIHYBRID CROSSES • A LITTLE DIFFERENT • H h G g X H h G g • What are the possible Allele combinations? • USE THE FOIL METHOD • First, Outer, Inner, Last

  26. FOIL – FIRST, OUTSIDE, INSIDE, LAST H h G g X H h G g 1. HG BOTH PARENTS ARE THE SAME 2. Hg 3. hG 4. hg

  27. NOW LET’S DO A DIHYBRID CROSS H h G g X H h G g HG Hg hG hg HG HHGG HHGg HhGG HhGg Hg HHGg HHgg HhGg Hhgg hG HhGG HhGg hhGG hhGg hg HhGg Hhgg hhGg hhgg

  28. WHAT ARE THE PHENOTYPIC RATIO’S? H h G g X H h G g DD: Dr: rD: rr: 9 3 3 1 HG Hg hG hg HG HHGG HHGg HhGG HhGg Hg HHGg HHgg HhGg Hhgg hG HhGG HhGg hhGG hhGg hg HhGg Hhgg hhGg hhgg

  29. 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 

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