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About Mendel and Genetics PG 101 • “The Father of Genetics” • Austrian Monk during the 19th century (1822-1884) • Studied Pea plants https://www.youtube.com/watch?v=GTiOETaZg4w Mendel’s Laws INDEPENDENT ASSORTMENT Allele pairs separate independently during the formation of gametes. Traits are transmitted to the offspring independently of one another LAW OF SEGREGATION When sex cells are made, then 2 “factors” separate… 1 per gamete Law of Segregation Mathematically proven through both generations Why did Mendel succeed? PG 101 • • • Peas were good choice. – Readily available – Easy to self-pollinate and cross-pollinate Good experimental choices. – Only chose “either-or” traits (purple OR white) – Started with true-breeding (purebred) plants – Followed for 3 generations (P, F1, F2) Kept good quantitative data. – Very large sample sizes Mendel’s Experiments (additional notes) Cross-pollinate 2 purebred plants (P generation) Resulting offspring (F1 generation) were all with dominant trait Results for F1 generation So where did the “white” go? Mendel allowed F1 plants to self-pollinate to see if they really had “lost” the white Results for F2 generation Approximately ¾ of F1 plants produced seeds that grew into purple flower plants The remaining ¼ made white flower plants Other traits… same results Mendel’s Hypotheses (bottom of pg 101) • Alternate versions of hereditary “factors” account for variation in inherited traits • For each trait, an organism inherits 2 “factors” (one from each parent) Mendel’s Hypotheses If the “factors” differ, one is dominant and is recessive The 2 “factors” for each trait separate during gamete production (meiosis) Law other of segregation - when sex cells are made… the 2 factors separate…1 per gamete Important Terms (Top of pg 101) Genotype Combination of genes (ex: Tt) Phenotype traits (ex: tall) Homozygous Two of same allele (ex: TT or tt) Heterozygous One of each allele (ex: Tt) Dominant Gets expressed; use capital letter Recessive Gets covered; use lowercase letter Putting it all together… Where are the “factors” that Mendel discovered? On our chromosomes How do these “factors” get passed on to offspring? Through the gametes during fertilization What do we call these “factors” now? Alleles (different forms of the same genes) Putting it all together… Why can’t we use mitosis to make gametes? Mitosis makes diploid cells with two sets of chromosomes (2n = diploid) * gametes must be haploid (n) having only one set of chromosomes What is the main goal of meiosis? Meiosis produces cells with only one set of chromosomes which are haploid gametes Punnett Square Basics Father genotypes always goes on top Mother genotypes always goes on the side Practice on your sheet! This is a monohybrid 1st square: AA x aa 2nd square: PP x pp (make your square) List genotypes & phenotypes List types of alleles Homozygous Heterozygous Punnett Square Basics Crosses can be larger then the simple 4 square- this is called a dihybrid Some AaBb you may see as: AaBb x When you cross this, you should “cross multiply” each individual by itself… i.e. (Aa)(Bb) x (Aa)(Bb) This will now look like this RECAP Mendel’s Laws: Independent assortment- allele pairs separate independently during the formation of gametes. Traits are transmitted to the offspring independently of one another Segregation- when sex cells are made, the 2 factors separate… 1 per gamete Discoveries: factors located on our chromosomes, through gametes during fertilization, now known as alleles (different forms of the same gene) Bell Ringer PG 102 Fertilization – fusing of sperm & egg Zygote – fertilized egg (diploid) which develops into an embryo Meiosis – type of cell division that produces egg & sperm; occurs in ovaries & testes Homologous Chromosomes- Carry same type of genes (though not necessarily the same version of that gene) Draw a dihybrid punnett square: 5 across, 5 down: making 25 squares… do not take up your whole page! Use your lines on the sheet!! Individual work- yes for a grade! Punnett square exercises Do the entire front page –get a check mark! We will work on the back page at a latter time! Recap of Mendel! Mendel’s Laws: Independent assortment- allele pairs separate independently during the formation of gametes. Traits are transmitted to the offspring independently of one another Segregation- when sex cells are made, the 2 factors separate… 1 per gamete Discoveries: factors located on our chromosomes, through gametes during fertilization, now known as alleles (different forms of the same gene) Why can’t we use mitosis to make gametes? Where are alleles located? How do alleles get passed down? Human Life Cycle Events PG 102 Fertilization – fusing of sperm & egg Zygote – fertilized egg (diploid) which develops into an embryo Meiosis – type of cell division that produces egg & sperm; occurs in ovaries & testes How do we get to haploid? PG 103 Meiosis is process to split chromosome # in half, making HAPLOID (n) CELLS (4) Result: 4 cells each with 1 of each type of chromosome Meiosis I – halves the chromosome # Meiosis II – reduces amount of DNA by half Meiosis Meiosis starts out with 1 cell that is DIPLOID (2n), (has both sets of chromosomes), and ends with 4 cells that are HAPLOID (n), (have only 1 set of chromosomes). Homologous Chromosomes • Homologous chromosomes – Carry same type of genes (though not necessarily the same version of that gene) – Ex: chromosome pair #1…both have gene for eye color in same spot…one codes for blue, other for brown Meiosis I: Reduce to Haploid PG 103 Draw each in their circle! Label & write the notes part under each KEY TERM: Synapsis Homologous chromosomes pair up (prophase I) WRITE THIS DEFINITION DOWN!! Meiosis I: Reduce to Haploid KEY TERM: Tetrad Group of 4 chromatids together during synapsis WRITE THIS DEFINITION DOWN!! Meiosis I: Reduce to Haploid KEY TERM: Chiasma (chiasmata) Crossing of non-sister chromatids (see crossing over) WRITE THIS DEFINITION DOWN!! Meiosis I: Reduce to Haploid Metaphase I: tetrads line up Anaphase I: homologous chromosomes separate Meiosis II: Reduce DNA Amount Draw each in their circle! Label & write the notes part under each Works just like mitosis Mitosis vs. Meiosis Mitosis cell division that produces 2 genetically identical diploid daughter cells ex. Somatic or body cells Meiosis cell division that produces 4 genetically different haploid daughter cells ex. Gametes or sex cells This type of cell division This type of cell division produces identical produces gametes which daughter cells which leads are all different and unique. to the development of tissues and organs Mitosis vs Meiosis So Many Possibilities… The positioning of tetrads in metaphase determines variability of resulting gametes So Many Possibilities… PG 104 If diploid # is 4 chromosomes 2 If diploid # is 6 chromosomes 2 x 2 = 4 possible gametes x 2 x 2 = 8 possible gametes If diploid # is 46 chromosomes (like us!) 2 x 2 x 2 x …x 2 = 8 million possible gametes And possibility after fertilization… 8 million x 8 million = 64 trillion possible individuals So Many Possibilities… Crossing over during meiosis I, nonsister chromatids of homologous chromosomes switch places Results in even more genetic variability Bell Ringer Page 104 comparing mitosis and meiosis Work No on this as individual work!! cell phones, no talking! Meiosis related to Mendel’s Laws Bottom of PG 103 Law of Independent Assortment: IA: a certain trait, the gamete can have either allele that is present in mom or dad MII: the 2 alleles will randomly move to opposite poles and 1 of those gametes produced will be fertilized How do Mendel’s Laws Relate to Meiosis? PG 110 Law of Independent Assortment Alleles for different traits are inherited independently or separately from each other. This occurs in Metaphase I… Meiosis related to Mendel’s Laws Law of Segregation: LoS: 2 factors that govern a trait separate from each other and go into different gametes MI: Homologous chromosomes pair up and separate form each other- just like Mendel said, even though he didn't know about meiosis How do Mendel’s Laws Relate to Meiosis? PG 103 Law of Segregation Every individual has two alleles of each gene and when gametes are produced, each gamete receives one of these allele. Happens during Anaphase I the homologous chromosomes separate (each chromatid has one allele per gene) Group Activity 4 people per lab table Draw what each phase looks like on the paper Write Write down what happens in each phase the genetic material name (i.e. chromatin, chromosome, tetrad, sister chromatids) Elbow partner work! Page 105 Front page only - Stages of Meiosis Label each phase, and put the correct number of order each phase goes in Label every structure within each phase Write down the definitions of the new terms under the correct phase they belong to: Tetrad Synapsis & Chiasma (Crossing over) Homologous Haploid Write pairs cells a brief statement of what is going on in each phase under the phases Punnett Squares PG102 Purebred- Homozygous dominant or recessive Hybrid- heterozygous traits Dominant- Capital letter-covers recessive trait Recessive- lower case letter- gets covered, unless homozygous Genotype- the letters used to represent the alleles Phenotype- physical appearance Punnett Square Basics PG 101 – review Parent genotypes listed on edges Fill in spaces…big letter listed first List genotype (G) and phenotype (P) including fractions, percent’s, or ratios G: 4/4 Aa P: 4/4 red Genotype vs Phenotype PG 101 Cross 2 heterozygous tall, purple pea plants with each other… PG 102 (T=tall, t=short, P=purple, p=white) TtPp x TtPp Cross 2 heterozygous tall, purple pea plants with each other… (T=tall, t=short, P=purple, p=white) TP TP Tp tP tp Tp tP tp Cross 2 heterozygous tall, purple pea plants with each other… (T=tall, t=short, P=purple, p=white) TP Tp tP tp TP TTPP TTPp TtPP TtPp Tp TTPp TTpp TtPp Ttpp tP TtPP TtPp ttPP ttPp tp TtPp Ttpp ttPp ttpp How many different phenotypes is that? Cross 2 heterozygous tall, purple pea plants with each other… (T=tall, t=short, P=purple, p=white) TP Tp tP tp TP TTPP TTPp TtPP TtPp Tp TTPp TTpp TtPp Ttpp tP TtPP TtPp ttPP ttPp tp TtPp Ttpp ttPp ttpp P: 9/16 tall, purple 3/16 tall, white 3/16 short, purple 1/16 short, white Work For Today! 1st – Work on page 106 (individual work) Problem Solving/Critical Thinking Raise hand when finished to get your grade 2nd – Genetic problems (pg106), Individual work Raise hand when finished to get your grade Bell Ringer Finish up your homework! You will have 10 minutes to complete it and turn it in! (problem solving & genetic problems) Testcross To determine genotype of a dominant phenotype organism Mendel’s Other Law What happens if you test 2 traits at the same time? (dihybrid cross) What if you cross purebred yellow-round with purebred green-wrinkled? Will traits “stick” to each other? Will traits “split up” from each other? Law of Independent Assortment Alleles are segregated (and inherited) separately Quiz time! Bell Ringer Individual Page work! 105- cell division concept map! You may listen to music while doing this assignment… Beyond Mendels’ Laws Mendel’s laws still apply, but many traits due to more complicated relationships between alleles Simple Dominance PG 107 A single dominant allele inherited from one parent is all that is needed for a person to show the dominant trait. Ex: -Earlobes attached is a recessive trait - Flower color in peas Sample Punnett Problem Cross a person who is heterozygous for dimples and a person who is recessive for no dimples Use the letter D & d for your dominant and recessive traits Write down how many will have and will not have the trait Incomplete Dominance Dominant partially covers recessive; heterozygotes will have an in-between phenotype Ex: curly-wavy-straight hair Sample Punnett Problem Cross a person who has straight hair (hh) with a person who has curly hair (HH) Write down the genotypes and phenotypes Codominance Both alleles dominant… both expressed (no blending in hetero’s) Ex: Human blood groups Sickle Cell Sample Problem Type AB – IA IB Sample Punnett Problem Cross a Sickle Cell Anemia (AA) with a person who is normal (NN) Cross a heterozygous and a normal Sample #1: G: 4/4 NA P: 4/4 s-c trait Sample #2: G: 2/4 NN, 2/4 NA P: 2/4 normal, 2/4 s-c Multiple Alleles Some traits have more than 2 possible alleles Ex: Human blood has A, B, and O Which other pattern does this reflect? codominance Sample Punnett Squares Practice doing your punnett squares at the bottom of 107, under Codominance and Multiple alleles Blood types: O= ii A= IA IA B= IB IB or IA i or IB I AB= IA IB Summary of “Dominance” Ranges from complete dominance to incomplete dominance to codominance Reflects expression of alleles, NOT one allele “covering up” another Does not reflect prevalence in population Recessive allele may be more common Sex-linked Gene Inheritance PG 108 In humans, sex-linked genes are the ones on the X chromosome Fathers pass these on to their daughters only and mothers pass these on to both sons & daughters Males traits more likely to have recessive sex-linked Sex-linkage – Sample Problem XX - female XY - male Sex-linked Inheritance Ex: male-pattern baldness; hemophilia; color-blindness Sample Punnett Problem PG 108 Cross a woman who is normal with a man who is colorblind Cross a woman who is a carrier for hemophilia with a normal man Cross a color-blind woman with a normal man Bell Ringer pg 114 If a black bunny (a dominant trait) is mated with a white bunny. The baby bunny is gray. What type of inheritance pattern does this express? Prove this with using a Punnett Square. Polygenic Inheritance pg 108 Due to more than one gene controlling a trait Has an “additive effect” Ex: human eye color, skin color, hair color, height The frequency of phenotypes of traits is controlled by PI follows a bell shaped curve Nature vs Nurture Ex: Flower color differs based on pH of soil Phenotype depends on environment & genes Ex: nutrition, physical activity, education, etc Norm of reaction = range of phenotype governed by a gene Some traits have no range (blood type) Some traits have large range (esp. polygenic) Mendelian Inheritance in Humans Not easy to study Generations Not enough offspring Cannot Must too long selectively breed find alternative methods to figure out human inheritance patterns Pedigrees PG 108 Traces traits through a family Used to determine genotypes & phenotypes Used to predict probability of certain traits in future offspring Pedigree Practice Purple = has disease Phenylketonuria (PKU) Is this trait due to a dominant or recessive gene? What are the genotypes for each individual? Human Disorders • Cystic fibrosis (recessive) – 1/2500 whites of European descent – 4% of whites are carriers (heterozygous) – Transport is abnormal…thick mucus Human Disorders Phenylketonuria(PKU) (autosomal recessive) rare condition in which a baby is born w/o the ability to properly break down amino acid called phenylalanine. products containing aspartame should be avoided Phenylalanine plays a role in the body's production of melanin, the pigment responsible for skin & hair color. Therefore, infants with the condition often have lighter skin, hair, and eyes Human Disorders Tay-Sachs Disease (recessive) 1/3600 of Ashkenazic (European) Jews Dysfunctional brain lipids Seizures, enzyme that does not break down blindness, motor & mental degeneration Human Disorders Duchenne’s Muscular Dystrophy (sex-linked recessive) Muscles Gene atrophy carried on X chromosome Recessives in the Population Recessives should be rare so chance that 2 people will have exact same recessives are low Chances related Lethal increase if the 2 people are recessive traits much more common than lethal dominant traits… Human Disorders Sickle-Cell 1/400 Disease (codominance) African Americans Substitution of 1 amino acid in hemoglobin Abnormal cell shape = less oxygen = many other symptoms (pleitropic) Heterozygotes symptoms may/may not have Codominance made Increases – both hemoglobins resistance to malaria Human Disorders Sickle-Cell Disease Human Diseases Hemophilia X-Linked recessive pattern (males are more affected, females carriers) 1/5000 Blood males inherited bleeding disorder doesn’t clot properly, may cause spontaneous bleeding, excessive bruising, bleed excessively during teething time, swollen bruised joints, frequent falling Human Dominant Disorders Achondroplasia Type of dwarfism 1/10,000 people Huntington’s disease Degenerative disease of nervous system starts ~35-45 yrs of age (after reproductive age) Bell Ringer PG 114 In chickens, rose comb (R) is dominant to single comb (r). A homozygous rose combed rooster is mated with a single combed hen. All of the chicks in F1 generation were kept together as a group for several years. They were allowed to mate only within their group. What is the expected phenotype of the F2 chicks? (use percentages). Multi-factor Disorders PG 109 Heart disease Diabetes Cancer Alcoholism Schizophrenia Manic-depression Trisomy 21 – Down Syndrome PG 117 Klinefelter’s Syndrome XXY (XXXXY) Male but often sterile; often with feminine characteristics XYY- Syndrome Male; perhaps taller than normal Other Aneuploids- pg 109 (write it down)! XXX female; nondistinguishable from XX X0 Turner’s syndrome Female; typically sterile 0Y Not viable; would not be born PG 114 Human blood types are one example of _________ ____ traits. _____________ _____________ is when there are more than 1 gene controlling a trait and has an “additive effect”. ________________ traces traits through a family, determines phenotypes & genotypes, and can predict probability of certain traits in future offspring. Quiz For Question 1, R=red, r=white 1. A) If a pure-bred red is crossed with a purebred white, what will the offspring be? B) Which inheritance pattern is this? For Questions 2, R=red, r=white 2. This plant shows incomplete dominance… If a pure-bred red is crossed with a pure-bred white, what will the offspring be? For Question 3, R=red, W=white 3. A) If a pure-bred red is crossed with a pure-bred white, what will the offspring be? B) Which inheritance pattern is this? Quiz 4. What is the name for this type of picture? 5. What gender is this person? 6. What defect does this person have? Quiz Purple = has disease White = does not have disease 7. Is this trait due to a dominant or recessive gene? 8. What is the likeliest genotype for Daniel? Quiz 9. Why can’t mitosis be used to make new sperm or egg cells? 10. In which phase of meiosis do tetrads form? 11. What is a tetrad? 12. What does Mendel’s law of independent assortment state? 13. What does Mendel’s law of segregation state?