* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Document
Survey
Document related concepts
Population genetics wikipedia , lookup
Genetically modified crops wikipedia , lookup
Inbreeding avoidance wikipedia , lookup
Transgenerational epigenetic inheritance wikipedia , lookup
Behavioural genetics wikipedia , lookup
Pharmacogenomics wikipedia , lookup
Genomic imprinting wikipedia , lookup
Hybrid (biology) wikipedia , lookup
Heritability of IQ wikipedia , lookup
Genetic drift wikipedia , lookup
Designer baby wikipedia , lookup
Microevolution wikipedia , lookup
Quantitative trait locus wikipedia , lookup
Transcript
Chapter 9, Section 1: Pre-Mendel Early Ideas about Heredity • The Blending Theory: – Main theory of inheritance until the late 19th century – Each parent contributed “factors” that were blended in the offspring • What was the problem with this theory? – All individuals of a population would eventually look the same. – Once blended, traits would never separate and show up in later generations. Chapter 9, Section 1: Mendel Gregor Mendel (1822 – 1884) • Augustinian monk who studied pea plants • Established the particulate theory of heredity • Significance: – Developed pure lines – Counted results and kept statistical notes • His work remained undiscovered until 1903. Mendel’s Research Character Dominant Trait Why did he research pea plants? Flower Color 1. They are normally self-pollinated, but can be cross-pollinated. Flower Position 2. They have several qualitative traits that are easy to distinguish Seed Shape i.e.,Tall vs. Short Purple Recessive Trait White Side Top Yellow Green Round Wrinkled Inflated Constricted Seed Color Pod Shape Pod Color Green Yellow Stem Length Tall Dwarf Mendel’s Research 1. 2. 3. 4. 5. Removed stamens from purple flower. Transferred pollen from stamens of white flower to pistil of purple flower. Pollinated flower matured into a pod. Planted seeds from pod. Examined offspring: All purple flowers… Watch this video clip, and see if you can explain why… Mendel’s Conclusions 1. Law of Segregation a. Factors (genes) for a particular trait occur in pairs b. For each trait, an organism inherits two genes, one from each parent. c. Dominant alleles mask recessive ones i. Exception 1: Incomplete Dominance ii. Exception 2: Co-dominance d. Two alleles for each trait segregate during gamete production Law of Segregation: Factors for a particular trait occur in pairs Homologous pair of Chromosomes Genes: The “factors” that control traits. Alleles: Different forms of a gene. Allele for White Flowers Locus for Flower Color Gene Allele for Purple Flowers Back to Mendel’s Conclusions W or w Ww w or w ww • Each individual is diploid – Diploid: Containing a double-set of chromosomes (2n) • Each gamete is haploid – Gamete: Reproductive cell (egg or sperm) – Haploid: Containing a single-set of chromosomes (n) Law of Segregation: One version of each gene is inherited from each parent Back to Mendel’s Conclusions Dominant alleles mask recessive ones P (Parent) Generation True-breeding parents 705 plants had purple flowers 224 plants had white flowers F1 (1st Filial) Generation Hybrid Offspring What happened to the recessive traits? F2 (2nd Filial) Generation What is the F2 ratio? 705:224 3:1 Dominant alleles mask recessive ones P Generation Phenotype (Appearance) Genotype (Genetic Makeup) Gametes Purple Flowers PP P White Flowers pp p F1 Generation Phenotype (Appearance) Genotype (Genetic Makeup) Gametes Purple Flowers Pp p P Punnett Square F2 Generation What is the Genotypic Ratio of the F2 Generation? PP:Pp:pp 1:2:1 P P PP p Pp p Pp pp What is the Phenotypic Ratio of the F2 Generation? 3: 1 Dominant alleles mask recessive 1 ones Genotype Phenotype PP (homozygous) Purple Pp (heterozygous) Purple Pp (heterozygous) Purple pp (homozygous) White Ratio = 1:2:1 Ratio = 3:1 3 2 1 1 Dominate alleles mask recessive ones Dominant phenotype, unknown genotype: PP or Pp? Recessive phenotype, known genotype: pp What would your If you have a dominant phenotype hypothesis be if the genotype was Pp? (like purple flowers) how would you design an experiment to determine P p (PP) P p if it was homozygous Pp Pp P p p p or heterozygous (Pp)? What would your hypothesis be if the genotype was PP? If PP, then all offspring purple: Pp Pp If Pp, then ½ offspring purple and ½ offspring white: pp Pp pp Pp This is called a test cross Back to Mendel’s Conclusions P Generation Phenotype(s): Red and White Genotype(s): CRCR and CWCW Gametes: CR and CW CR CW F1 Generation Phenotype: Pink Genotype: CRCW Gametes: CR and CW ½ CR ½ CW F2 Generation ½ ½ CR CRCR Exception to Dominant Alleles Masking Recessive Alleles: Incomplete Dominance: Pink Snapdragons ½ CW CRCW CR ½ CRCW CWCW CW Exception to Dominant Alleles Masking Recessive Alleles: Co-dominance: Blood Types Back to Mendel’s Conclusions Law of Segregation: Two alleles for each trait segregate during gamete production Back to Mendel’s Conclusions This is a process called meiosis: Specifically it is “crossing over,” which occurs very early during Prophase I of Meiosis Mendel’s Conclusions 2. Law of Independent Assortment The law of segregation followed one single trait at a time, such as flower color. What if two traits were followed? Two hypotheses were written and experimented on to determine if traits were: – – Dependent (linked), or Independent (not linked) If the genes are not connected, then they should segregate independently. P Following two traits: Seed shape and seed color Gametes YR F1 Ova yr F2 yr YyRr YR YR Sperm yr Hypothesis: If the genes for seed shape and color are connected in some way, then the dominant R and Y alleles and the recessive r and y alleles will be segregated as matched sets in the gametes. What are the genotypes of the P Generation? YYRR What does the P Generation pass on to F1? yr YR F1 Phenotype? F1 Genotype? What does the F1 Generation pass on to F2? Combine the sperm and ova to produce the offspring in F2 yr What do you expect the phenotype will be when YR and YR are combined? What will the Genotype be when YR and YR are combined? Law of Independent Assortment yyrr Gametes YyRr Ova YR Yr yR YR Yr YYRR YYRr YyRR Sperm yR YYRr yr YyRR YYrr Phenotypic Ratios YyRr YyRr Yyrr yyRr 9/16 Yellow & Round 3/16 Green & Round 3/16 Yellow & Wrinkled 1/16 Green & Wrinkled Yyrr yyRR Now try to do it on your own! What are the phenotypic ratios? YyRr YyRr yyRr yyrr Significance of Mendel’s Research 1. Probability was introduced as a biological concept: The number of times an event occurs The number of trials 2. Punnett Square was introduced as a tool Probability: Segregation of alleles into ova Pp x Pp The number of times an event occurs The number of trials ½ ½ P P ½ Segregation of alleles into sperm p P P ½ ½x½= ¼ p P P ¼ p How do you get a genotypic ratio of 1:2:1 from these numbers? p ¼ p p ¼ Back to Mendel’s Principles Punnett Square Exercise One-trait cross The allele for the hairy trait is “H,” while the allele for the hairless trait is “h.” Make a cross between two homozygotes for each of these traits. Punnett Square Exercise One-trait cross Henry VIII divorced six of his wives (two of whom were executed) for not bearing him any sons. Use Mendelian Genetics to prove to King Henry that it wasn’t his wives’ fault. Remember: Females are XX and Males are XY. Punnett Square Exercise One-trait cross In a populations of hamsters, brown fur is dominant (B), and white fur is recessive (b). Predict the offspring from the cross of a white hamster and a brown hamster if the brown hamster's mother was white. Punnett Square Exercise Two-trait cross Following two traits: Kernel shape: Plump vs. withered (P and p) and Kernel color Red vs. yellow (R and r) Predict the cross between a homozygous recessive corn plant and a homozygous dominant corn plant. Punnett Square Exercise Two-trait cross Now take the offspring from that cross, and self-pollinate that plant. What is the phenotypic ratio of this cross? Punnett Square Exercise Two-trait cross My pet guinea pigs (Joni and Chachi) are going to have little guinea pigs. What is the possibility that their offspring will have long hair, if I know that Joni and Chachi are heterozygous for the following traits? Black fur (B) White fur (b) Long hair (L) Short hair (l)