Bio 31 Lecture 4: Gene Segregation and Interaction PDF

BIO 31 (Principles of Genetics) Lecture 4 Gene Segregation and Interaction Prepared by: Helen LV. Ebuña Department of Agronomy & Plant Breeding College of Agriculture, Central Mindanao University Musuan, 8710 Bukidnon...

BIO 31 (Principles of Genetics) Lecture 4 Gene Segregation and Interaction Prepared by: Helen LV. Ebuña Department of Agronomy & Plant Breeding College of Agriculture, Central Mindanao University Musuan, 8710 Bukidnon https://study.com/cimages/multimages/16/464px-independent_assortment__segregation.svg8896999839333204121.png Bio31 Lecture 4. Prepared by HLVEbuña TERMINOLOGIES 1. Factor: A particle or unit in the organism which is responsible for the inheritance and expression of a particular character. 2. Gene: Mendel’s factor is now known as gene. A gene is a particular segment of a DNA molecule which determines the inheritance and expression of a particular character. 3. Alleles or Allelomorphs: Two or more alternative forms of a gene. E.g. In pea, the gene for seed shape may occur in two alternative forms: round (R) and wrinkled (r). Round and wrinkled forms of the gene are alleles of each other. Alleles occupy same locus on homologous chromosomes 2 Bio31 Lecture 4. Prepared by HLVEbuña TERMINOLOGIES 4. Dominant: The trait which appears in the F1 (first filial generation) hybrid is called the dominant trait (Dominant Allele). 5. Recessive: trait, one which is suppressed (does not appear) in the F1 hybrid is called the recessive trait (recessive allele). 6. Genotype: The genetic make-up or genic constitution of an individual (which he/she inherits from the parents) is called the genotype e.g., the genotype of pure round- seeded parent will be RR 3 Bio31 Lecture 4. Prepared by HLVEbuña TERMINOLOGIES 7. Phenotype: The appearance (morphology, physiology, and behavior) of an organism for any trait or traits is called the phenotype, e.g. for seeds, round shape or wrinkled shape is the phenotype. 8. Homozygous: An individual possessing (receiving from parents) identical alleles for a trait is said to be homozygous or pure for that trait, e.g. plant with RR alleles is homozygous for the seed shape. A homozygous always breeds true for that trait. 9. Heterozygous: An individual receiving dissimilar alleles for a trait is said to be heterozygous or impure for that trait, e.g. a plant with Rr alleles is heterozygous for the seed shape. Heterozygous is also called a hybrid. Bio31 Lecture 4. Prepared by HLVEbuña 4 TERMINOLOGIES 10.Parent generation: The parents used for the first cross represent the parent (or P) generation. 11. F1 generation: The progeny produced from a cross between two parents (P) is called First Filial or F1 generation. 12. Inbreeding: When the individuals of a progeny (e.g. F1 generation) are allowed to cross with each other, it is called inbreeding. ✓ Mating of closely related individuals. 13. F2 generation: The progeny resulting from self hybridization or inbreeding of F1 individuals is called Second Filial or F2 generation. Bio31 Lecture 4. Prepared by HLVEbuña 5 TERMINOLOGIES 15.Monohybrid cross: The cross between two parents differing in a single pair of contrasting characters is called monohybrid cross and the F1offspring as the monohybrid(heterozygous for one trait only). 15. Monohybrid ratio: The phenotypic ratio of 3 dominants : 1 recessive obtained in the F2 generation from the monohybrid cross is called monohybrid ratio. 16. Dihybrid cross: The cross between two parents in which two pairs of contrasting characters are studied simultaneously for the inheritance pattern. The F1 offspring is described as dihybrid or double heterozygous (i.e. with dissimilar alleles for two characters). 6 Bio31 Lecture 4. Prepared by HLVEbuña Mendel’s Hybridization Experiments Involved testing 7 characters individually by hybridizing 2 varieties showing alternative traits E.g. tall x short; green-seeded x yellow-seeded The parental plants (P generation) were from pure breeding lines (homozygous) The F1 generation produces all round seeds When F1 plants were self-fertilized, round and wrinkled seeds appear in F2 generation https://images.app.goo.gl/ahhNiyNd6Ly9KbdZA Bio31 Lecture 4. Prepared by HLVEbuña  Results of All Mendel’s Crosses in Which Parents Differed in One Character Parental phenotype F1 F2 F2 percentage F2 ratio 1. Round×wrinkled All round 5474 round; 1850 wrinkled 74.74; 25.26 2.96:1 seeds 2. Yellow×green seeds All yellow 6022 yellow; 2001 green 75.06; 24.94 3.01:1 3. Purple×white petals All purple 705 purple; 224 white 75.89; 24.11 3.15:1 4. Inflated×pinched All inflated 882 inflated; 299 pinched 74.68; 25.32 2.95:1 pods 5. Green×yellow pods All green 428 green; 152 yellow 73.79; 26.21 2.82:1 6. Axial×terminal All axial 651 axial; 207 terminal 75.87; 24.11 3.14:1 flowers 7. Long×short stems All long 787 long; 277 short 73.97; 26.03 2.84:1 Bio31 Lecture 4. Prepared by HLVEbuña Mendel’s Hybridization Experiments The following pattern was established from summarizing the results: 1. For any character, F1 showed one of the alternative traits. Such character that was shown was dominant and the character that was hidden was recessive. 2. Reciprocal crosses gave the same result 3. The trait that did not appear in the F1 reappeared in the F2 but in a frequency of ¼ of the total number https://images.app.goo.gl/UJPEXt8fzWqEUTAa7 Bio31 Lecture 4. Prepared by HLVEbuña Mendel’s Hybridization Experiments Q: What can be deduced from these observations? Each parent must have contributed equally to the progeny F1 contains the two alternative factors or is heterozygous These two factors or alleles separate or segregate from each other during gamete formation in the F1 https://images.app.goo.gl/f6VVguuHb22vAo3EA https://images.app.goo.gl/UJPEXt8fzWqEUTAa7 some gametes carry R and others r. Bio31 Lecture 4. Prepared by HLVEbuña Mendel’s Hybridization Experiments These two type of gametes occur at equal frequences in the ova and in the pollen grains Self fertilization of the F1 causes the random combination of the male and female gametes to form the F2 embryos This accounts for the 1:2:1 genotypic ratio and 3:1 The inheritance of seed characteristics follows https://images.app.goo.gl/f6VVguuHb22vAo3EA https://images.app.goo.gl/UJPEXt8fzWqEUTAa7 complete dominance. Bio31 Lecture 4. Prepared by HLVEbuña Law of Dominance In a hybrid union, the allele which expresses itself phenotypically is the dominant allele while the other allele which fails to express itself phenotypically is the recessive https://microbenotes.com/wp- content/uploads/2021/06/Mendels- allele. The hybrid individual shows Law-of-Dominance-Pea-Plant.jpeg phenotypically only the dominant character. The law of dominance is often described as Mendel’s first law of inheritance. Bio31 Lecture 4. Prepared by HLVEbuña Pea traits studied by Mendel Bio31 Lecture 4. Prepared by HLVEbuña Dominant and recessive characters in some plants and animals Examples Dominant Recessive Appearance of F1 hybrids PLANTS Sorghum (i) Pearly grain Chalky grain Pearly (ii) Awnless Awned Awnless Maize Full Endosperm Shrunken Full endosperm Rice Starchy Glutinous Starchy endosperm endosperm ANIMALS Rabbit Black coat white coat Black Mice Normal body dwarf Normal size Man (i) Brown eyes blue eyes Brown (ii) Short stature tall short Bio31 Lecture 4. Prepared by HLVEbuña  Law of Segregation On the basis of the results obtained for the monohybrid crosses, Mendel formulated the law of segregation, also called Mendel’s second law of heredity. The law states that unit of hereditary characters (e.g. round vs. wrinkled) occur in pairs and that in the formation of gametes during meiosis, these separate from each other so that only one member of the pair goes into a particular gamete. It is a matter of chance whether a particular gamete gets the dominant or recessive allele. Fusion of male and female gametes during fertilization to form the embryo will restore the diploid chromosome number Bio31 Lecture 4. Prepared by HLVEbuña https://cdn.kastatic.org/ka-perseus-images/233cb1be87053c9e4d58d20d75ca2cb310f70712.png  Law of Segregation when a pair of alleles is brought together in hybrid union, the members of the allelic pair remain together without A Punnett square mixing, diluting or can be used to altering each other predict genotypes and separate or (allele combinations) segregate from and phenotypes each other when (observable traits) the hybrid forms of offspring from gametes. genetic crosses. Bio31 Lecture 4. Prepared by HLVEbuña  Results of All Mendel’s Crosses in Which Parents Differed in One Character Parental phenotype F1 F2 F2 percentage F2 ratio 1. Round×wrinkled All round 5474 round; 1850 wrinkled 74.74; 25.26 2.96:1 seeds 2. Yellow×green seeds All yellow 6022 yellow; 2001 green 75.06; 24.94 3.01:1 3. Purple×white petals All purple 705 purple; 224 white 75.89; 24.11 3.15:1 4. Inflated×pinched All inflated 882 inflated; 299 pinched 74.68; 25.32 2.95:1 pods 5. Green×yellow pods All green 428 green; 152 yellow 73.79; 26.21 2.82:1 6. Axial×terminal All axial 651 axial; 207 terminal 75.87; 24.11 3.14:1 flowers 7. Long×short stems All long 787 long; 277 short 73.97; 26.03 2.84:1 Bio31 Lecture 4. Prepared by HLVEbuña  Law of Independent Assortment Mendel’s Law of Segregation applies to the behavior of a single pair of alleles or a single gene. When two or more genes are considered simultaneously, the Law of Independent Assortment applies The law states that genes for different characteristics are inherited independently of one another or alleles of different gene pairs separate independently from each other and randomly combine during meiosis Mendel based this law on the results of his dihybrid crosses https://study.com/cimages/multimages/16/464px-independent_assortment__segregation.svg8896999839333204121.png Bio31 Lecture 4. Prepared by HLVEbuña  Law of Independent Assortment "When a dihybrid (or a polyhybrid ) forms gametes, (i) each gamete receives one allele from each allelic pair and (ii) the assortment of the alleles of different traits during the gamete formation is totally independent of their original combinations in the parents. In other words, each allele of any one pair is free to combine with any allele from each of the remaining pairs during the formation for the gametes This is known as the Law of Independent Assortment of characters. It is also referred to as Mendel’s third law of heredity https://study.com/cimages/multimages/16/464px-independent_assortment__segregation.svg8896999839333204121.png Bio31 Lecture 4. Prepared by HLVEbuña Law of Independent Assortment https://study.com/cimages/multimages/16/464px-independent_assortment__segregation.svg8896999839333204121.png Bio31 Lecture 4. Prepared by HLVEbuña Law of Independent Assortment https://study.com/cimages/multimages/16/464px-independent_assortment__segregation.svg8896999839333204121.png Bio31 Lecture 4. Prepared by HLVEbuña  Law of Independent Assortment https://study.com/cimages/multimages/16/464px-independent_assortment__segregation.svg8896999839333204121.png https://images.app.goo.gl/MVgnM7P3HEwuXGQZA Bio31 Lecture 4. Prepared by HLVEbuña Law of Independent Assortment https://study.com/cimages/multimages/16/464px-independent_assortment__segregation.svg8896999839333204121.png Bio31 Lecture 4. Prepared by HLVEbuña  Formulas NO. OF GENE KINDS OF KINDS OF KINDS OF PAIRS GAMETES GENOTYPES PHENOTYPES 1 2 3 2 2 4 9 4 3 8 27 8 4 16 81 16 n 2n 3n 2n Bio31 Lecture 4. Prepared by HLVEbuña Chi-Square test Q: How do we know if our data fit any of the Mendelian ratios? ✓A statistical test that can test out ratios is the Chi-Square or Goodness of Fit test. Chi-Square Formula for n>2 Degrees of freedom (df) = n-1 where n is the number of classes Bio31 Lecture 4. Prepared by HLVEbuña  Chi-Square test E.g. To test if the following data follows a 9:3:3:1 ratio: Observed Values Expected Values 315 Round, Yellow Seed (9/16)(556) = 312.75 Round, Yellow Seed 108 Round, Green Seed (3/16)(556) = 104.25 Round, Green Seed 101 Wrinkled, Yellow Seed (3/16)(556) = 104.25 Wrinkled, Yellow 32 Wrinkled, Green (1/16)(556) = 34.75 Wrinkled, Green 556 Total Seeds 556.00 Total Seeds Bio31 Lecture 4. Prepared by HLVEbuña  Chi-Square test E.g. To test if the following data follows a 9:3:3:1 ratio: Number of classes (n) = 4 df = n-1 = 4-1 = 3 Chi-square value = 0.47 Bio31 Lecture 4. Prepared by HLVEbuña Chi-Square test A Chi-Square Table Probability Degrees of Freedom 0.9 0.5 0.1 0.05 0.01 1 0.02 0.46 2.71 3.84 6.64 2 0.21 1.39 4.61 5.99 9.21 3 0.58 2.37 6.25 7.82 11.35 4 1.06 3.36 7.78 9.49 13.28 5 1.61 4.35 9.24 11.07 15.09 Bio31 Lecture 4. Prepared by HLVEbuña Chi-Square test Decision: Since the calculated Chi-Square value is lesser than the tabular Chi-Square value at 5% level of significance, we do not reject the null hypothesis that the observed values followed the Mendelian ratio of 9:3:3:1. https://images.app.goo.gl/cDBycvtugWLF1yCq5 Bio31 Lecture 4. Prepared by HLVEbuña