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Variation & genetics
- 1. VARIATION & GENETICS CHAPTER22 2ND YEAR BIOLOGY
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- 3. MENDLE’S LAWS OFINHERITENCE
- 4. Seven Contrasting Pairsstudied by Mendle
- 5. Due to itsshort life span Short time between generation Rapid growth Many generations can be raised within short period of time Capability of self fertilization as well as cross fertilization Easy to handle
- 6. Monohybrid Cross F3 Generationresults 1/3 of F2 Round produced only round (True breeding like P1) 2/3 of F2 round produced both round and wrinkled in 3:1 ratio(Monohybrids like F1 round) F2 wrinkled produced wrinkled
- 7. Mendles’s Interpretation Particulate HerditaryFactor (Elementen) Homozygous (RR)________Homozygote Hetrozygous(Rr)_________Hetrozygote F1 Segregation Gametes 1/2 1/2 Rr R r Monohybrid Cross Interpretation Phenotypic Ratio 3:1 Genotypic Ratio 1:2:1 1/4 = RR (Homozygous round) 2/4 = Rr (Hetrozygous round) 1/4 = rr (Homozygous Wrinkled)
- 8. Used to testthe genotype of an individual showing a .dominant phenotype
- 10. Probability is chanceof an event to occur In monohybrid cross there is a independent chance for a seed to be round is ¾ or wrinkled ¼. When two independent events are occurring simultaneously the ratio of each joint phenotypic combination can be obtained by multiplying the probabilities of individual phenotypes and it is a product rule.
- 12. Independent assortment ofgenes depends upon independent assortment of their chromosomes The genes present on homologous chromosomes does not assort independently henxe co assortment happened. They are linked on homologous chromosomes as linkage group. Mendles knew nothing about chromosomes The traits studied by Mendle confined to these four chromosomes who assort independently while other three present far away from each other on homologous chromosomes hence no linkage possible so assort independently. 1865---Mendle presented his work to Brunn Society for study of natural Science 1866—work Published 1990 his work was rediscovered and acknowledged after 34 Years
- 14. 1) Complete Dominance 2)Incomplete Dominance 3) Codominance 4) Over Dominance
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- 18. Over Dominance In overdominance the expression of heterozygous allele become more dominant than both homozygous allele
- 19. Genes having morethan two altered forms or alleles are multiple alleles Well understood by ABO blood group System in humans.
- 20. Karl Land Steiner in 1901 Encodedby single polymorphic gene I on chromosome 9. Gene has three multiple alleles IA, IB and i. Blood group start their expression at early embryonic stage and keep on expressing till death.
- 21. Anti Bodies appearin Plasma during few months after birth Naturally occurring in absence of corresponding antigen Phenotype A will agglutinate or clump any RBC with B antigen and vice versa AB phenotype has neither A nor B Antibody and O phenotype has neither A nor B Antigen The Blood serum containing antibodies is called antiserum Any blood transfusion is safe if its not causing agglutination in recipient. Agglutination leads to serious results because clumped cells can not pass through fine capillaries ultimately leading to capillary blockage.
- 22. A child havingAB Phenotype can nor be the child of O type phenotype Similarly Blood group type B can not be the father of child having A type phenotype whose mother is of phenotype O.
- 23. Rh Blood GroupSystem Encoded by three genes C, D and E which occupy two tightly linked loci. Allele of D occupy one locus while other locus is occupied by C and E alternatively. Prime importance is of D. Gene D has two alleles D (dominant) and d (recessive). DD or Dd= Rh+ dd= Rh- Rh antibody production requires stimulus from respective Rh antigen.
- 24. Erythroblastosis foetalis If Fathers genotypeis DD then all of their offspring Rh+ and If the genotype is Dd then half of their offspring Rh+. Liver and Spleen of baby swell due to rapid production of RBC. The breakdown product of RBC is Bilirubin. Bilirubin damages brain cells and turns his skin and whites of the eye yellow. (Jaundice)
- 25. When an effectcaused by a gene or gene pair at one locus interferes with or hides the effect caused by another gene or gene pair at another locus.
- 26. Expression of IAor IB gene depends upon another gene present on chromosome no.19. H gene insert a precursor substance which insert a sugar molecule onto surface molecule (glycoprotein) of RBC. Respective antigen then attach to that sugar molecule But the recessive hh gene lack that precursor and no sugar molecule is inserted. Antgens don’t get space to adhere hence fall away. Their RBCs lack antigens A or B but genes IA and IB present. So they look phenotypically O but they are not O genotypically
- 31. Numerous characters controlledby thousands of genes residing on limited no of chromosomes. All genes present on homologous chromosomes linked together through linkage group. staying together of all of genes together on same chromosome is called linkage. No of linkage group corresponds to the no of homologous pairs of chromosomes present. genes for colour blindness, haemophilia, gout etc form 1 linkage group on X chromosome. Gene for sickle cell anemia, leukemia and albinism make another linkage group on human chromosome 11. Gene linkage minimizes the chances of genetic recombination.
- 33. Exchange of segments betweennon sister chromatids of homologous chromosomes during meiosis. Crossing over produces genetic variations among offspring's
- 35. Proportion of recombinanttypes between two gene pairs as compared to sum of all combinations Recombinant frequency is directly proportional to distance b/w the linked gene loci. Genes can be mapped on a chromosome on the basis of their recombination frequency.
- 36. SEX CHROMOSOME 8 chromosomesin 4 homologous pair Morgan notices notable difference in male and female drosophila Female had 2 similar rod shaped x chromosome Male had one rod shaped x chromosome but other morphologically different j shaped Y chromosome
- 37. 46 chromosomes in23 pairs are present 23rd pair is different and is call sex chromosome Male is heteromorphic having a x and a very short y chromosome Female is homomorphic having same 2 x chromosomes SRY is male determining gene Male= 11 pairs of autosomes with only 1 x chromosome Female= 11 pairs of autosomes with 2 x chromosome
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- 42. Syndrome Drosophila Humans Turner’sSyndrom (XO) Sterile male Sterile female Klinefelters Syndrome (XXY) Sterile Female Sterile male
- 43. X-Y System X-chromosome autosomebalance system for sex determination Correns (1970) discovered pollens to be sex determining Many microorganisms like Yeast don not have sex chromosomes Depends on genic system for determination of sex
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- 49. Normal trichromatic colourvision is based on three kinds of cone cells Red Opsin is on X Chromosome Green Opsin is on X Chromosome Blue Opsin Is in Autosome 7 Mutation in opsin genes gives 3 types of blindness Dichromat---perceive 2 primary colours Monochromat—perceive one coloue Tricchromat—perceive no colour Protanopa—Red Blindness Deuteranopa—Green Blindnedd Tritanopia—Blue Blindness
- 52. LIMITED TO ONESEX DUE TO ANATOMICAL DIFFERENCE Affects structure present only in males or females E.g. Genes for milk yields in Cows SEX INFLUENCES TRAIT Occurs in both male and females but more common in one sex Controlled by allele that is dominant in one sex but recessive in other sex. E.g. Baldness
- 53. Type I IDDM& Type II NIDDM Type I-- immune disorder Insulin gene is located on short arm of chromosome 11 Polymorphism and genetic variation within this locus is responsible for diabetes Type I susceptibility Multifactorial or Polygenic MODY Blood Pressure is also a multifactorial trait.
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