CHAPTER 10 mendel

CHAPTER 10 mendel - CHAPTER 10 MENDEL & MEIOSIS...

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Unformatted text preview: CHAPTER 10 MENDEL & MEIOSIS 10.1 MENDEL’S LAWS OF HEREDITY HEREDITY I. WHY MENDEL SUCCEEDED Gregor Mendol – 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 SUBJECT Used garden peas to study 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 RESEARCHER USED CAREFULLY CONTROLLED EXPERIMENTS STUDIED ONE TRAIT AT A TIME KEPT DETAILED DATA II. MENDEL’S MONOHYBRID CROSSES CROSSES MENDEL STUDIED 7 TRAITS CAREFULLY Pg. 262 – figure 10.3 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 1 GENERATION A. ST Mendel crossed two plants – 1 tall & 1 short (they came from tall & short populations) 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 (the short plants were totally excluded) B. THE 2 B. ND 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!!!!!!) TO GO ANY FURTHER, WE MUST UNDERSTAND ALLELES, DOMINANCE, & SEGREGATION DOMINANCE, 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 ALLELES THESE 2 ALLELS ARE NOW KNOWN TO BE FOUND ON COPIES OF CHROMOSOMES – ONE FROM EACH PARENT THE RULE OF DOMINANCE THE 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 DOMINANCE 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 THE LAW OF SEGREGATION THE 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 SEGREGATION 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 F1 GENERATION T T FATHER T t T t MOTHER T t t t 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 PHENOTYPES & GENOTYPES PHENOTYPES PG. 264 PHENOTYPE – THE WAY AN ORGANISM LOOKS AND BEHAVES – ITS PHYSICAL CHARACTERISTICS (i.e. – TALL, GREEN, BROWN HAIR, BLUE EYES, ETC.) GENOTYPE – THE GENE COMBONATION (ALLELIC COMBINATION) OF AN ORGANISM – (i.e. – TT, Tt, tt, ETC.) HOMOZYGOUS – 2 ALLELES ARE THE SAME ANSWER ON YOUR SHEET ANSWER TRAITS = BLUE SKIN & YELLOW SKIN BB – IS THIS HOMOZYGOUS OR HETEROZYGOUS? HOMOZYGOUS IS BLUE SKIN OR YELLOW SKIN DOMINANT? BLUE MENDEL’S DIHYBRID CROSSES MENDEL’S 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 DIHYBRID 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 ALL THE OFFSPRING ARE ROUND DOMINANT) DIHYBRID CROSS – 1ST DIHYBRID GENERATION CONT’D GENERATION 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 DIHYBRID GENERATION 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) EXPLANATION OF 2ND EXPLANATION GENERATION GENERATION MENDEL CAME UP W/ 2ND LAW – THE LAW OF INDEPENDENT ASSORTMENT GENES FOR DIFFERENT TRAITS ARE INHERITED INDEPENDENTLY FROM EACH OTHER THIS IS WHY MENDEL FOUND ALL THE DIFFERNENT COMBONATIONS OF TRAITS PUNNETT SQUARES PUNNETT A QUICK WAY TO FIND THE GENOTYPES IN UPCOMING GENERATIONS 1ST DRAW A BIG SQUARE AND DIVIDE IT IN 4’S PUNNETT SQUARE PUNNETT CROSS T T X Tt CONT’D CONT’D T T X T t T T T T T T T t T t T t DIHYBRID CROSSES DIHYBRID A LITTLE DIFFERENT H h G g X H h G g MUST FIND OUT ALL THE POSSIBLE ALLELIC COMBONATIONS USE THE FOIL METHOD LIKE IN MATH 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 CROSS H h G g X H h G g hg HG HG Hg hG HHGG HHGg HhGG HhGg HHgg HhGg Hhgg Hg HHGg hG HhGG HhGg hhGG hhGg hg HhGg Hhgg hhGg hhgg WHAT ARE THE PHENOTYPIC RATIO’S? RATIO’S? H h G g X H h G g DD: 9 HhGg Dr: 3 HhGg Hhgg rD: 3 rr: 1 HG HG Hg hG HHGG HHGg HhGG HHgg hg Hg HHGg hG HhGG HhGg hhGG hhGg hg HhGg Hhgg hhGg hhgg PROBABILITY PROBABILITY WILL REAL LIFE FOLLOW THE RESULTS FROM A PUNNETT SQUARE? NO!!!!!! – A PUNNETT SQUARE ONLY SHOWS WHAT WILL PROBABLY OCCUR IT’S A LOT LIKE FLIPPING A COIN – YOU CAN ESTIMATE YOUR CHANCES OF GETTING HEADS, BUT REALITY DOESN’T ALWAYS FOLLOW PROBABILITY 10.2 MEIOSIS 10.2 GENES, CHROMOSOMES, AND NUMBERS CHROMOSOMES HAVE 100’S OR 1000’S OF GENES GENES FOUND ON CHROMOSOMES DIPLOID & HAPLOID CELLS DIPLOID ALLBODY CELLS (SOMATIC CELLS) HAVE CHROMOSOMES IN PAIRS BODY CELLS ARE CALLED DIPLOID CELLS (2n) HUMANS HAVE THE 2n # OF CHROMOSOMES DIPLOID AND HAPLOID CELLS CONT’D CONT’D HAPLOID CELLS ONLY HAVE 1 OF EACH TYPE OF CHROMOSOME (DIPLOID CELLS HAVE 2 OF EACH TYPE) SYMBOL IS (n) SEX CELLS HAVE THE n # OF CHROMOSOMES HOMOLOGOUS CHROMOSOMES HOMOLOGOUS HOMOLOGOUS CHROMOSOMES ARE THE PAIRED CHROMOSOMES THAT CONTAIN THE SAME TYPE OF GENTIC INFORMATION, SAME BANDING PATTERNS, SAME CENTROMERE LOCATION, ETC. THEY MAY HAVE DIFFERENT ALLELES, SO NOT PERFECTLY IDENTICAL WHY DO THEY HAVE DIFFERENT ALLELES? CAME FROM DIFFERENT PARENTS WHY MEIOSIS? WHY MITOSIS – RESULTS IN GENETICALLY IDENTICAL OFFSPRING – INCLUDING THE # CHROMOSOMES WHAT WOULD HAPPEN IF THE EGG AND SPERM HAD THE SAME # OF CHROMOSOMES AS THE BODY CELLS? EGG = 46 CHROMOSOMES SPERM = 46 CHROM. ZYGOTE = 46 + 46 = 92 CHROMOSOMES = NOT HUMAN MEIOSIS MEIOSIS A TYPE OF CELL DIVISION WHICH PRODUCES GAMETES CONTAING HALF THE NUMBER OF CHROMOSOMES AS THE BODY CELLS 2 STAGES – MEIOSIS I & MEIOSIS II START W/ 1 DIPLOID CELL, END UP W/ 4 HAPLOID CELLS (GAMETES) 4 DAUGHTER CELLS ARE GENETICALLY DIFFERENT FROM EACH OTHER AND MOTHER CELL INTRO TO MEIOSIS CONT’D INTRO SPERM – MALE GAMETE (n) EGG – FEMALE GAMETE (n) FERTILIZATION PRODUCES A ZYGOTE (2n) THIS TYPE OF REPRODUCTION IS CALLED SEXUAL REPRODUCTION STAGES OF MEIOSIS MEIOSIS MEIOSIS I PROPHASE I, METAPHASE I, ANAPHASE I, TELOPHASE I (PMAT) MEIOSIS II PROPHASE II, METAPHASE II, ANAPHASE II, TELOPHASE II (PMAT) IMPORTANT THINGS TO KNOW IMPORTANT CROSSING OVER – OCCURS DURING PROPHASE I CREATES GENETIC VARIABILITY (RECOMBINATION OF GENES) IN MEIOSIS I, HOMOLOGOUS CHROMOSOMES SEPARATE (ANAPHASE I) IN MEIOSIS II, SISTER CHROMATIDS SEPARATE TETRAD – WHAT THE HOMOLOGOUS CHROMOSOMES ARE CALLED WHEN THEY PAIR UP DURING PROPHASE I ...
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This note was uploaded on 11/18/2011 for the course BI 107 taught by Professor Fuller during the Spring '08 term at Montgomery College.

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