General Biology 1 Fall 2024 Introduction to Genetics PDF

General Biology 1 Fall 2024 Introduction to Genetics Part -1 Prof : Dr. Vincent Gagnon Book Raven, Biology, 13th edition  Introduction to Genetics Study guide: Topic...

General Biology 1 Fall 2024 Introduction to Genetics Part -1 Prof : Dr. Vincent Gagnon Book Raven, Biology, 13th edition  Introduction to Genetics Study guide: Topic References (13th Ed) Section 12.1 to 12.4, Identify Mendel's Principles. Be prepared to support the use of garden peas pages 231-239 as an experimental tool. Study all figures in this chapter Demonstrate how Mendel determined each principle using the mono- and Section 12, Figures dihybrid crosses. Be able to identify the parental and first or second filial 12.5 and 12. 7 pages generation in any genetic cross. 235 & 237. Relate Mendel's model to the scientific method and identify his hypotheses Section 12, pages 231- for the monohybrid and dihybrid experiment. 236. Define test cross and understand its importance in determining genotypes Section 12, pages 236- of dominant phenotypes. Use a Punnett square to determine the outcome 237, Figure 12.8 of a cross and calculate phenotypic ratios.  Introduction to Genetics Gregor Mendel Born in 1822 to Austrian parent, Mendel was first educated at the Monastery and then went to study chemistry and physics at the University of Vienna. University of Vienna He failed his license to become a teacher. He went back to the Monastery and became a monk and started to study the heredity of peas.  Introduction to Genetics Why use peas ? Other research showed that pea hybrids could be produced. Many pea varieties were available. Peas are small plants, fast and easy to grow.  Introduction to Genetics Why use peas ? Other research showed that pea hybrids could be produced. Many pea varieties were available. Peas are small plants, fast and easy to grow. Peas can self-fertilize Some plants have both sex in their flower!  Introduction to Genetics Why use peas ? Other research showed that pea hybrids could be produced. Many pea varieties were available. Peas are small plants, fast and easy to grow. Peas can self-fertilize or be cross-fertilized.  Introduction to Genetics 3 step of Mendel’s experimental method 1. Produce true-breeding strains for each trait he was studying. 2. Cross-fertilize true-breeding strains having alternate forms of a trait. 3. Allow the hybrid offspring to self-fertilize for several generations and count the number of offspring showing each form of the trait.  Introduction to Genetics 1. True-breeding strains : Variety which over multiple generations of self Only plant crossing give descendants with characteristics the seed identical to the parent plant. from a purple flower Ex.: Self crossing until you obtain only purple flowers.  Introduction to Genetics 1. True-breeding strains : Mendel produced true-breeding pea strains for 7 different traits. Flower color, seed color, seed texture, pod color, pod shape, flower position, plant height. Each trait had 2 variants.  Introduction to Genetics 2. Cross-fertilize true-breeding strains: What would be the colour of the flower from crossing two true breed parental generations, one with a purple flower and another with a white flower? ?  Introduction to Genetics 2. Cross-fertilize true-breeding strains: What would be the colour of the flower from crossing two true breed parental generations, one with a purple flower and another with a white flower? The pollen (male gametes) is carried from the anthers to the stigma, a sticky organ that traps pollen and allows the pollen to move down the pistil to the female gametes (ovary). Pollen Ovary  Introduction to Genetics 2. Cross-fertilize true-breeding strains: What would be the colour of the flower from crossing two true breed parental generations, one with a purple flower and another with a white flower? To prevent the pea plant that was receiving pollen from self-fertilizing and confounding his results, Mendel painstakingly removed all of the anthers from the plant’s flowers before they had a chance to mature.  Introduction to Genetics 2. Cross-fertilize true-breeding strains: What would be the colour of the flower from crossing two true breed parental generations, one with a purple flower and another with a white flower?  Introduction to Genetics 2. Cross-fertilize true-breeding strains: What would be the colour of the flower from crossing two true breed parental generations, one with a purple flower and another with a white flower? Strangely the first filial generation (F1) only produce purple flower, no white, no mix! Reciprocal cross: male and female cross give the same type of offspring then female and male cross.  Introduction to Genetics 2. Cross-fertilize true-breeding strains: What would be the colour of the flower from crossing two true breed parental generations, one with a purple flower and another with a white flower? True breed parental F1 generation generations (hybrid) F1 generation: Fist filial generation is the offspring produced by crossing 2 true-breed strains. For every trait Mendel studied, all F1 plants resembled only 1 of the parent: − Referred to this trait as dominant. − Alternative trait was recessive No plants with characteristics intermediate between the 2 parents were produced. No blending of traits  Introduction to Genetics 3. Self-fertilize hybrid offspring for several generations: F1 generation (hybrid) F2 generation: Second filial generation are the offspring resulting from the self- fertilization of F1 plants.  Introduction to Genetics 3. Self-fertilize hybrid offspring for several generations: F1 generation (hybrid) F2 generation: Second filial generation are the offspring resulting from the self- fertilization of F1 plants. Although hidden in the F1 generation, the recessive trait had reappeared among some F2 individuals. Counted a 3:1 phenotypic ratio.  Introduction to Genetics 3. Self-fertilize hybrid offspring for several generations: F2 generation: 2.82 to 1 3.15 to 1 2.95 to 1 3.01 to 1 3.14 to 1 2.96 to 1 2.84 to 1 Counted proportions of traits is always about 3 to 1 ratio (3:1).  Introduction to Genetics 3. Self-fertilize hybrid offspring for several generations: F3 generation: Third filial generation are the offspring resulting from the self- fertilization of F2 plants. Mendel discovered the ratio is actually 1:2:1 − 1 true-breeding dominant plant. − 2 not-true-breeding dominant plants. − 1 true-breeding recessive plant.  Introduction to Genetics Conclusion: His plants did not show intermediate traits (no pale purple). For each pair, one trait was dominant, the other recessive. Pairs of alternative traits examined were segregated among the progeny of a particular cross. Alternative traits were expressed in the F2 generation in the ratio of ¾ dominant (purple) to ¼ recessive (white).  Introduction to Genetics Mendel’s five-element model 1. Parents transmit discrete factors (those are genes on chromosomes, which were unknown at the time of Mendel!). 2. Each individual receives one copy of a “gene” from each parent. 3. Not all copies of a gene are identical − Allele: alternative form of a gene (flower purple or white). − Homozygous: 2 of the same allele. − Heterozygous: different alleles. 4. Alleles remain discrete, no blending (no pale purple).  Introduction to Genetics Mendel’s five-element model 5. Presence of allele does not guarantee expression. − Dominant allele: Is always expressed (denote with a CAPITAL letter). − Recessive allele: Is hidden by dominant allele. Only express when there are two recessive alleles present (small letter). − Phenotype: Physical appearance. − Genotype: Total set of alleles an individual contains  Introduction to Genetics Mendel Law of Segregation − The law states that paired unit factors (gene alleles) must segregate equally into gametes such that offspring have an equal likelihood of inheriting either factor. − Mendel had no knowledge of chromosomes, genes, alleles or meiosis, since it had not yet been described at the time.  Introduction to Genetics Mendel Law of Independent Assortment − Genes do not influence each other with regard to the sorting of alleles into gametes, and every possible combination of alleles for every gene is equally likely to occur when they are located on different chromosomes.  Introduction to Genetics Using a Punnett square to analyze Mendel’s cross Image you want to know the genotype and phenotype of true breed parental generations (one purple with one white). True breed parental generations  Introduction to Genetics Using a Punnett square to analyze Mendel’s cross Image you want to know the genotype and phenotype of true breed parental generations (one purple with one white). True breed parental generations Each true-breeding parent makes only one type of gamete. P P Dominant purple allele  Introduction to Genetics Using a Punnett square to analyze Mendel’s cross Image you want to know the genotype and phenotype of true breed parental generations (one purple with one white). True breed parental generations Each true-breeding parent makes only one type of gamete. P p P p Dominant Recessive purple white allele allele  Introduction to Genetics Using a Punnett square to analyze Mendel’s cross Image you want to know the genotype and phenotype of true breed parental generations (one purple with one white). Punnett squares True breed parental generations Each true-breeding parent makes only one type of gamete. F1 p p P P p P Possible children's  Introduction to Genetics Using a Punnett square to analyze Mendel’s cross Image you want to know the genotype and phenotype of true breed parental generations (one purple with one white). Punnett squares True breed parental generations Each true-breeding parent makes only one type of gamete. F1 p p P Pp Pp P p P Pp Pp Genotype Possible children's  Introduction to Genetics Using a Punnett square to analyze Mendel’s cross Image you want to know the genotype and phenotype of true breed parental generations (one purple with one white) Punnett squares True breed parental generations Each true-breeding parent makes only one type of gamete F1 p p − Dominant allele: P P Pp Pp − Recessive allele: p P Pp Pp Phenotype Possible children's  Introduction to Genetics Punnett square  Introduction to Genetics F1 Punnett square F1 are all purple heterozygotes. Make two types of gametes and produce three phenotypes of F2 offspring: - PP homozygous dominant (purple). - Pp heterozygous (also purple). - pp homozygous recessive (white). F2  Introduction to Genetics Test cross: To test his model further, Mendel devised a simple and powerful procedure called the testcross. In a testcross, an individual with unknown genotype is crossed with the homozygous recessive genotype. For example: When you have a purple-flowered pea plant, it is impossible to tell whether such a plant is homozygous (PP) or heterozygous (Pp) simply by looking at it since purple allele is dominant! ? ? or PP Pp Homozygous Heterozygous  Introduction to Genetics Test cross: To test his model further, Mendel devised a simple and powerful procedure called the testcross. In a testcross, an individual with unknown genotype is crossed with the homozygous recessive genotype. For example: When you have a purple-flowered pea plant, it is impossible to tell whether such a plant is homozygous (PP) or heterozygous (Pp) simply by looking at it since purple allele is dominant! ? ? Test cross or PP Pp Homozygous Heterozygous  Introduction to Genetics Test cross: For example: When you have a purple-flowered pea plant, it is impossible to tell whether such a plant is homozygous (PP) or heterozygous (Pp) simply by looking at it, since purple allele is dominant! Punnett squares Punnett squares p p p p Heterozygous Homozygous P P p P Pp PP Genotype Genotype  Introduction to Genetics Test cross: For example: When you have a purple-flowered pea plant, it is impossible to tell whether such a plant is homozygous (PP) or heterozygous (Pp) simply by looking at it, since purple allele is dominant! Punnett squares Punnett squares p p p p Heterozygous Homozygous P Pp Pp P Pp Pp p pp pp P Pp Pp Pp PP Genotype Genotype  Introduction to Genetics Test cross: For example: When you have a purple-flowered pea plant, it is impossible to tell whether such a plant is homozygous (PP) or heterozygous (Pp) simply by looking at it, since purple allele is dominant! Punnett squares Punnett squares p p p p Heterozygous Homozygous P Pp Pp P Pp Pp p pp pp P Pp Pp Pp PP Genotype Genotype  Introduction to Genetics Monohybrid crosses Cross to study only 2 variations of a single trait. Example: flower colour True breed parental generations Dihybrid crosses Examination of 2 separate traits in a single cross (genes located on different chromosomes). Produced true-breeding lines for 2 traits. Example: - Seed colour (Yellow or Green) - Seed shape (Round or wrinkle)  Introduction to Genetics Dihybrid crosses Examination of 2 separate traits in a single cross. True breeding parent of each traits Dominant Recessive RR YY rr yy The F1 generation of a dihybrid cross shows only the dominant phenotypes for each trait. Punnett squares ry ry RY RrYy RrYy RY RrYy RrYy  Introduction to Genetics Dihybrid crosses F1 self-fertilizes Self pollination of F1 hybrid Rr Yy Rr Yy The F2 generation shows all four possible phenotypes in a set ratio 9:3:3:1 The phenotype ratio of F2 show the independent assortment of the gene of each trait (they are on different chromosomes)  Introduction to Genetics Principle of Independent Assortment In a dihybrid cross, the alleles of each gene assort independently. The segregation of different allele pairs is independent. Independent alignment of different homologous chromosome pairs during metaphase I leads to the independent segregation of the different allele pairs. P p In other word the genes that we are testing are on different chromosomes.