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D.N.A AP Biology When meiosis goes wrong! The most common malfunction in meiosis is called nondisjunction This is when the chromosomes DO NOT come apart in anaphase AP Biology Nondisjunction This can result in some gametes with too many chromosomes AP Biology EXAMPLE: DOWN SYNDROME •When nondisjunction occurs on the 21st chromosomes AP Biology •2 of our 46 chromosomes are sex chromosomes •Males have the combination XY •Females have the combination XX AP Biology EXAMPLE: TURNER AND KLINEFELTER’S SYNDROME •Males with Klinefelter’s Syndrome have XXY AP Biology EXAMPLE: TURNER AND KLINEFELTER’S SYNDROME •Individuals with Turner Syndrome have XO AP Biology CHECK FOR UNDERSTANDING What is nondisjunction? When the chromosomes don’t separate correctly in meiosis AP Biology CHECK FOR UNDERSTANDING What are the sex chromosomes for females? XX What are the sex chromosomes for males? XY AP Biology CHECK FOR UNDERSTANDING What might be the chromosomes in a male if nondisjunction occurred? XXY What might be the chromosomes in a female if nondisjunction occured? XO AP Biology Looking at Chromosomes A Karyotype is a picture of human chromosomes It shows all 46 chromosomes matched up with their homologous pairs A karyotype can allow a doctor or scientist to spot any chromosome abnormalities. AP Biology KARYOTYPES Normal Human Karyotype AP Biology Is this a male or female? Karyotyping Chromosomal Mutations Stations! Read the descriptions of abnormalities on your worksheet 5 -6 people at each station You will spend 5 minutes at each station After the 5 minutes are up, you will rotate to the next station AP Biology Warm Up All of the following are true about the karyotype above except: A. The karyotype is of a female B. The karyotype is of a female with 47 chromosomes C. The karyotype is of a normal human D. The karyotype is of an abnormal human AP Biology D.N.A Objective: SWBAT explain how Mendel’s particulate mechanism differed from the blending theory of inheritance. Quarter 2 Reflection Questions 1. How did you perform academically in Ms. Nakamura’s class for 2nd quarter? 2. How did you perform behaviorally in Ms. Nakamura’s class for 2nd quarter? rd quarter? 3. How can you improve for 3 4. How can Ms. Nakamura improve for 3rd quarter to help you have a better learning environment? AP Biology Genetics & The Work of Mendel AP Biology 2006-2007 Gregor Mendel Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas used experimental method used quantitative analysis collected data & counted them AP Biology excellent example of scientific method Mendel’s work Bred pea plants Pollen transferred from white flower to stigma of purple flower P cross-pollinate true breeding parents (P) P = parental raised seed & then observed traits (F1) F = filial allowed offspring to self-pollinate & observed next generation (F2) AP Biology anthers removed all purple flowers result F1 self-pollinate F2 Mendel collected data for 7 pea traits AP Biology Looking closer at Mendel’s work P F1 true-breeding true-breeding X purple-flower peas white-flower peas 100% purple-flower peas Where did the white flowers go? 100% generation (hybrids) self-pollinate F2 generation AP Biology 75% purple-flower peas White flowers came back! 25% white-flower peas 3:1 What did Mendel’s findings mean? Traits come in alternative versions purple vs. white flower color alleles different alleles vary in the sequence of nucleotides at the specific locus of a gene some difference in sequence of A, T, C, G purple-flower allele & white-flower allele are two DNA variations at flower-color locus different versions of gene at same location on homologous chromosomes AP Biology Traits are inherited as discrete units For each characteristic, an organism inherits 2 alleles, 1 from each parent diploid organism inherits 2 sets of chromosomes, 1 from each parent homologous chromosomes like having 2 editions of encyclopedia Encyclopedia Britannica Encyclopedia Americana AP Biology What are the advantages of being diploid? What did Mendel’s findings mean? Some traits mask others purple & white flower colors are separate traits that do not blend I’ll speak for both of us! purple x white ≠ light purple purple masked white dominant allele functional protein masks other alleles mutant allele producing malfunctioning protein recessive allele allele makes a malfunctioning protein AP Biology wild type allele producing functional protein homologous chromosomes Genotype vs. phenotype Difference between how an organism “looks” & its genetics phenotype description of an organism’s trait the “physical” genotype description of an organism’s genetic makeup X P Explain Mendel’s results using …dominant & recessive …phenotype & genotype AP Biology purple white F1 all purple Making crosses Can represent alleles as letters flower color alleles P or p true-breeding purple-flower peas PP true-breeding white-flower peas pp PP x pp X P purple white F1 AP Biology all purple Pp Looking closer at Mendel’s work P true-breeding true-breeding X purple-flower peas white-flower peas phenotype PP pp 100% purple-flower peas F1 genotype 100% generation (hybrids) Pp Pp Pp Pp self-pollinate F2 75% purple-flower peas 25% white-flower peas generation AP Biology ? ? ? ? 3:1 Punnett squares Pp x Pp F1 Aaaaah, phenotype & genotype can have different ratios generation (hybrids) % genotype male / sperm female / eggs P p PP 25% 75% Pp P PP % phenotype 50% Pp Pp p AP Biology Pp pp pp 25% 25% 1:2:1 3:1 Phenotype vs. genotype 2 organisms can have the same phenotype but have different genotypes purple PP purple Pp heterozygous homozygous dominant How do you determine the genotype of an individual with with a dominant phenotype? AP Biology Can’t tell by lookin’ at ya! Test cross Breed the dominant phenotype — the unknown genotype — with a homozygous recessive (pp) to determine the identity of the unknown allele How does that work? x is it PP or Pp? AP Biology pp How does a Test cross work? Am I this? Or am I this? x PP pp x Pp p p P Pp Pp P Pp Pp P Pp Pp p pp pp AP Biology 100% purple p pp p 50% purple:50% white or 1:1 D.N.A Objective: SWBAT to apply mathematical routines to determine Mendelian patterns of inheritance. In humans the allele for albinism is recessive to the allele for normal skin pigmentation. If two heterozygtoes have children, what is the chance that a child will have normal skin pigment? What is the chance that a child will be albino? A a Normal Pigment chance: AA or Aa (75%) Albino chance: 25% aa Aa AA A If the child is normal, what is the chance that 2/3 or 67% Aa aa a it is a carrier (heterozygous) for the AP Biology albino allele? Mendel’s 1st law of heredity PP Law of segregation during meiosis, alleles segregate P P homologous chromosomes separate each allele for a trait is packaged into a separate gamete p pp p P Pp AP Biology p Law of Segregation Which stage of meiosis creates the law of segregation? Metaphase 1 Whoa! And Mendel didn’t even know DNA or genes existed! AP Biology Monohybrid cross Some of Mendel’s experiments followed the inheritance of single characters flower color seed color monohybrid crosses AP Biology Dihybrid cross Other of Mendel’s experiments followed the inheritance of 2 different characters seed color and seed shape dihybrid crosses AP Biology Mendel was working out many of the genetic rules! Dihybrid cross P true-breeding yellow, round peas Y = yellow R = round true-breeding green, wrinkled peas x YYRR yyrr y = green r = wrinkled yellow, round peas F1 100% generation (hybrids) YyRr self-pollinate F2 generation AP Biology 9:3:3:1 9/16 yellow round peas 3/16 green round peas 3/16 yellow wrinkled peas 1/16 green wrinkled peas What’s going on here? If genes are on different chromosomes… how do they assort in the gametes? together or independently? YyRr YR AP Biology yr Is it this? Or this? YR YyRr Yr Which system explains the data? yR yr YyRr Dihybrid cross YR YyRr x YyRr YR Yr yR yr or YR Yr yr YyRr Yyrr yR YyRR YyRr yyRR yyRr yr AP Biology YYRr YyRr YYrr Yyrr yyRr yyrr yR yr 9/16 yellow round 3/16 green round YR YYRR YYRr YyRR YyRr Yr YyRr BINGO! 3/16 yellow wrinkled 1/16 green wrinkled Mendel’s 2nd law of heredity Can you think of an exception to this? Law of independent assortment different loci (genes) separate into gametes independently green non-homologous chromosomes align independently classes of gametes produced in equal amounts round only true for genes on separate chromosomes or yellow YR = Yr = yR = yr wrinkled on same chromosome but so far apart that crossing over happens frequently YyRr Yr Yr 1 AP Biology yR : yR 1 YR : YR 1 yr : yr 1 Law of Independent Assortment Which stage of meiosis creates the law of independent assortment? Remember Mendel didn’t even know DNA —or genes— existed! AP Biology Metaphase 1 EXCEPTION If genes are on same chromosome & close together will usually be inherited together rarely crossover separately “linked” The chromosomal basis of Mendel’s laws… Trace the genetic events through meiosis, gamete formation & fertilization to offspring AP Biology Review: Mendel’s laws of heredity Law of segregation monohybrid cross single trait each allele segregates into separate gametes established by Metaphase 1 Law of independent assortment dihybrid (or more) cross 2 or more traits genes on separate chromosomes assort into gametes independently established by Metaphase 1 AP Biology EXCEPTION linked genes metaphase1 Mendel chose peas wisely Pea plants are good for genetic research available in many varieties with distinct heritable features with different variations flower color, seed color, seed shape, etc. Mendel had strict control over which plants mated with which each pea plant has male & female AP Biology structures pea plants can self-fertilize Mendel could also cross-pollinate plants: moving pollen from one plant to another Mendel chose peas luckily Pea plants are good for genetic research relatively simple genetically most characters are controlled by a single gene with each gene having only 2 alleles, one completely dominant over the other AP Biology Any Questions?? AP Biology 2006-2007