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Deviations From Mendelian Genetics

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Published in: Biology
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Genetics notes for Class XII students

P. V / Mumbai

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  1. MANDELIAN GENETICS Crosses that deviate from Mandelian inherintance
  2. TO THE STUDENTS, QExplain recessive lethal vallele, QCalculate genotypic and phenotypic ratios for lethal alleles (2:1) QExplain linked genes, Obescribe the effects of linked genes with crossing over on the dihybrid test cross ratio. QExplain sex-linked genes,
  3. Mendelian Inheritance Monohybrid No. Character Genes/ character Alleles/gene Phenotype Genotype F2 generation Phenotypic ratio Genotypic rotio One One Two Two Three 3 Red: I White Flower colour Gene for flower colour Dominant: Red (R) Recessive: White (r) Red (RR, Rr) and White (rr)
  4. RECESSIVE LETHAL GENE The gene which, when homozygous for a certain allele, bring about death Example: coat color of mice Dominant : Yellow (Y) Recessive : Grey (y)
  5. WILD nee grey-colored fur (agouti) Y allele dominant for fur color & RECESSIVE LETHAL GENE MUTANT yellow-colored fur recessive for the lethal characteristic
  6. Coat color of mice RECESSIVE LETHAL GENE Yellow P: G: Yellow (Die) Yellow K Yellow Yellow 2 Grey 1
  7. LINKED GENES Genes that are on the same chromosome are linked do not undergo independent assortment Linkage group Mendel Character No. Gene No allele/ gene Location of gene Two Two Two/gene, dominant & recessive Different homologous chromosome a b
  8. Figure 9.25 Linked genes (i.e., on same chromosome) [don't confuse with 'sex-linked'!] Without crossing over, how many types of gametes can be made? Just TWO - Tetrad AB and Crossing over With crossing over, how many types of gametes can be made? FOUR-AA and ab & Ab and aB. Parental gametes Recombinant gametes WEB
  9. Example: body color and wing size of Drosophila WILDTYPE (gray with normal wings) b+ b vg+ vg 9 OFFSPRING EXPECTED (independent assortment) OBSERVED PARENTS x WILD TYPE BLACK- VESTIGIAL GRAY- VESTIGIAL BLACK- NORMAL b vg+ vg bb vg vg b vg vg bb vg+ vg 575 575 575 575 x-..........-.....-.....-...-.--.-v--...-..-..-..-.........-.-....--.,c e--......-................-......-.v-...............-.-....-.-.----.-./ BLACK WITH VESTIGIAL WINGS b b vg vg Result of test cross is not in Parental phenotypes Recombinant phenotypes 965 944 206 185
  10. Drosophi/a - body colour & wing size B - grey body (dominant) b - black (recessive) V - normal (dominant) v - vestigial (recessive) e Grey,normal Black, vestigial x bv/bv Gamete BV/BV BV BV bv bv BV/bv Fl genot e BV/bv F henot pe BV/bv BV/bv All grey, normal Fl self cross
  11. x Gamete Grey,normal BV/bv BV Grey,normal BV/bv BV bv BV/bv bv F2 genot e Ratio genotype F2 phenotype Ratio phenotype BV/BV 1 BV/bv Grey, 2 normal 3 bv/bv 1 Black, vestigial 1
  12. You Knoweeo?? SEX DETERMINATION IN HUMANS 44 + Parents XY Sperm Y X xx Ova 44 + Zygotes (offspring)
  13. SEX LINKED GENES Genes carried on the sex chromosomes 13 19 14 20 15 21 10 16 22 11 12 SCIENCEPhOtOLlBRARY
  14. SEX LINKED GENES Eg : 1, Haemophilia (XH:Normal allele; Xh:Allele cause haemophilia 2, Colour blindness xHxH xHxh xhxh Female normal Female carrier XHY Male normal XhY Male haemophilia/ patient Female haemophilia/ patient
  15. Parent gamete progeny xcxc Color blind x XCY Normal xcxc xcxc XCY XCY 100% carrier 100% color blind

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