CHAPTER 9 MENDEL & MEIOSIS

10.1 MENDEL’S LAWS OF 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

copyright cmassengale Mendelian Genetics 12/6/2018 Gregor Johann Mendel Between 1856 and 1863, Mendel cultivated and tested some 28,000 pea plants He found that the plants' offspring retained traits of the parents Called the “Father of Genetics" copyright cmassengale

Particulate Inheritance Mendelian Genetics 12/6/2018 Particulate Inheritance Mendel stated that physical traits are inherited as “particles” Mendel did not know that the “particles” were actually Chromosomes & DNA copyright cmassengale

copyright cmassengale Mendelian Genetics 12/6/2018 Genetic Terminology Trait - any characteristic that can be passed from parent to offspring Heredity - passing of traits from parent to offspring Genetics - study of heredity copyright cmassengale

copyright cmassengale Mendelian Genetics 12/6/2018 Designer “Genes” Alleles - two forms of a gene (dominant & recessive) Dominant - stronger of two genes expressed in the hybrid; represented by a capital letter (R) Recessive - gene that shows up less often in a cross; represented by a lowercase letter (r) copyright cmassengale

1. MENDEL CHOSE HIS SUBJECT CAREFULLY 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

Reproduction in Flowering Plants Mendelian Genetics 12/6/2018 Reproduction in Flowering Plants Pollen contains sperm Produced by the stamen Ovary contains eggs Found inside the flower Pollen carries sperm to the eggs for fertilization Self-fertilization can occur in the same flower Cross-fertilization can occur between flowers copyright cmassengale

copyright cmassengale Mendelian Genetics 12/6/2018 How Mendel Began Mendel produced pure strains by allowing the plants to self-pollinate for several generations copyright cmassengale

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

Mendel’s Experimental Methods Mendelian Genetics 12/6/2018 Mendel’s Experimental Methods Mendel hand-pollinated flowers using a paintbrush He could snip the stamens to prevent self-pollination Covered each flower with a cloth bag He traced traits through the several generations copyright cmassengale

II. MENDEL’S MONOHYBRID CROSSES MENDEL STUDIED 7 TRAITS CAREFULLY 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 (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 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!!!!!!)

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 tt DOMINANT TRAIT 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

Applying the Law of Segregation Mendelian Genetics 12/6/2018 Applying the Law of Segregation copyright cmassengale

- the law of segregation explained the heredity of the f2 generation FATHER MOTHER F1 GENERATION T t T t t t 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 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 HETEROZYGOUS – 2 ALLELES DIFFERENT

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

ALL THE OFFSPRING ARE ROUND 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 - 9 FOUND ROUND/GREEN - 3 FOUND WRINKLED/YELLOW - 3 FOUND WRINKLED/GREEN - 1 ( 9 : 3 : 3 : 1 RATIO)

EXPLANATION OF 2ND 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

Summary of Mendel’s laws Mendelian Genetics 12/6/2018 Summary of Mendel’s laws LAW PARENT CROSS OFFSPRING DOMINANCE TT x tt tall x short 100% Tt tall SEGREGATION Tt x Tt tall x tall 75% tall 25% short INDEPENDENT ASSORTMENT RrGg x RrGg round & green x round & green 9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow pods copyright cmassengale

copyright cmassengale Mendelian Genetics 12/6/2018 Incomplete Dominance F1 hybrids have an appearance somewhat in between the phenotypes of the two parental varieties. Example: snapdragons (flower) red (RR) x white (rr) RR = red flower rr = white flower r R copyright cmassengale

copyright cmassengale Mendelian Genetics 12/6/2018 Codominance Problem Example: homozygous male Type B (IBIB) x heterozygous female Type A (IAi) IB IA i IAIB IBi 1/2 = IAIB 1/2 = IBi copyright cmassengale

copyright cmassengale Mendelian Genetics 12/6/2018 Codominance Question: If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents? boy - type O (ii) X girl - type AB (IAIB) copyright cmassengale

copyright cmassengale Mendelian Genetics 12/6/2018 Codominance Answer: IB IA i IAIB ii Parents: genotypes = IAi and IBi phenotypes = A and B copyright cmassengale

copyright cmassengale Mendelian Genetics 12/6/2018 Sex-linked Traits Traits (genes) located on the sex chromosomes Sex chromosomes are X and Y XX genotype for females XY genotype for males Many sex-linked traits carried on X chromosome copyright cmassengale

copyright cmassengale Mendelian Genetics 12/6/2018 Sex-linked Traits Example: Eye color in fruit flies Sex Chromosomes XX chromosome - female Xy chromosome - male fruit fly eye color copyright cmassengale

copyright cmassengale Mendelian Genetics 12/6/2018 Codominance Answer: IB IA i IAIB ii Parents: genotypes = IAi and IBi phenotypes = A and B copyright cmassengale

PUNNETT SQUARES A QUICK WAY TO FIND THE GENOTYPES IN UPCOMING GENERATIONS 1ST DRAW A BIG SQUARE AND DIVIDE IT IN 4’S

PUNNETT SQUARE CROSS T T X Tt

CONT’D T T X T t T T T T T T T t T t T t

DIHYBRID CROSSES 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

H h G g X H h G g 1. HG BOTH PARENTS ARE THE SAME 2. Hg 3. hG 4. hg 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

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

WHAT ARE THE PHENOTYPIC RATIO’S? H h G g X H h G g DD: Dr: rD: rr: 9 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

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 GENES, CHROMOSOMES, AND NUMBERS CHROMOSOMES HAVE 100’S OR 1000’S OF GENES GENES FOUND ON CHROMOSOMES

DIPLOID & HAPLOID CELLS ALL BODY 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 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 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

ZYGOTE = 46 + 46 = 92 CHROMOSOMES = WHY MEIOSIS? 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 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 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 I MEIOSIS II PROPHASE I, METAPHASE I, ANAPHASE I, TELOPHASE I (PMAT) MEIOSIS II PROPHASE II, METAPHASE II, ANAPHASE II, TELOPHASE II (PMAT)

IMPORTANT THINGS TO KNOW 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