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SEX- LINKED INHERITANCE. Lateral view of a male Fruit Fly (Drosophila melanogaster) showing its red wild type eye. LM.

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Presentation on theme: "SEX- LINKED INHERITANCE. Lateral view of a male Fruit Fly (Drosophila melanogaster) showing its red wild type eye. LM."— Presentation transcript:

1 SEX- LINKED INHERITANCE

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3 Lateral view of a male Fruit Fly (Drosophila melanogaster) showing its red wild type eye. LM

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5 P: FEMALE DROSOPHILAX MALE DROSOPHILA RED- EYED ♀WHITE-EYED ♂ F1: ALL RED-EYED OFFSPRING CONCLUSION: RED-EYE GENE IS DOMINANT P (FROM F1) RED- EYED ♀ XRED-EYED ♂ F2: 3/4 RED-EYED ; 1/4 WHITE-EYED ♀ AND ♂♂ !

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9 P: X R X R XX r Y G: 1/1 X1/2, 1/2 F1: 1/2 X R X r ; 1/2X R Y CONCLUSION: ALL RED-EYED OFFSPRING P (FROM F1): X R X r X X R Y G: 1/2 X R, 1/2 X r x1/2 X R, 1/2 Y F2: 1/4X R X R ; 1/4 X R X r ; 1/4 X R Y ; 1/4 X r Y * XRXR XrXr Y ¾ RED-EYED ♀ AND ♂¼ WHITE-EYED ♂

10 P: RED EYED FEMALE FROM F1 x ORIGINAL WHITE-EYED MALE F1: Female offspring ; male offspring (50% red; 50% white) ( 50%red; 50% white) Conclusion: Eye-color gene is found on the X chromosome and there is no corresponding allele on the Y chromosome P : X R X r X X r Y G: 1/2 X R, 1/2 X r X1/2 X r, 1/2 Y F1: 1/4X R X r ; 1/4 X r X r ; 1/4 X R Y ; 1/4 X r Y RED-EYED ♀WHITE-EYED ♀RED-EYED ♂WHITE -EYED ♂ TEST CROSS

11 SEX- LINKED INHERITANCE IN HUMANS X-LINKED TRAITS IN HUMAN (HEMOPHILIA, DUCHENNE MUSCULAR DYSTROPHY, COLORBLINDNESS)

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13 HEMOPHILIA (a) P: Homozygous normal female X hemophiliac male X H X H X X h Y G: 1/1 X H 1/2 X h ; 1/2 Y F1 : 1/2 X H X h ; 1/2 X H Y (carrier – female) (normal - male) H: DOMINANT GENE FOR HEMOPHILIA h: RECESSIVE GENE FOR HEMOPHILIA

14 (b) P: Heterozygous (carier) female X normal male X H X h X X H Y G: 1/2 X H, 1/2 X h 1/2 X H, 1/2 Y F1 : 1/4 X H X H ; 1/4 X H X h ; 1/4 X H Y ; 1/4 X h Y Homozygouscarrier ♀ normal hemophiliac normal ♀ Normal phenotyped ♀

15 (c) P: Heterozygous (carrier) female X hemophiliac male X H X h X X h Y G: 1/2 X H, 1/2 X h 1/2 X h, 1/2 Y F1 : 1/4 X H X h ; 1/4 X h X h ; 1/4 X H Y ; 1/4 X h Y carrier ♀ hemophiliac ♀ normal hemophiliac

16 DUCHENNE MUSCULAR DYSTROPHY

17 COLORBLINDNESS Normal ♀color blind♂carrier♀ X R X R X r Y X R X r Normal ♂colorblind ♀ X R Y X r X r

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20 The pattern of inheritance of X- linked traits; A man inherits his X chromosome and all his X- linked traits from his mother A woman inherits one X chromosome from her mother and one from her father A defective X chromosome in a man is always passed to each daughter but never to a son A defective X chromosome in a woman has a 50% chance of being passed to each son and daughter

21 Y-LINKED TRAITS IN HUMAN Ichtyosis hystrix (balık pulluluk) Hair on the rim of the ears joined 2nd and 3rd toes A pedigree chart: Inheritance of Y-linked trait in a family

22 Ichtyosis hystrix : balık pulluluk

23 Name: Radhakant Bajpai, India. Length: 13.2cm (5.2 inches) Hair on the rim of the ears

24 A map of the human X and Y chromosomes, showing the locations of some of the genes that cause disease Duchenne muscular dystrophy Hemophilia A Colorblindness Hemophilia B Diabetes insipidus Genes for testes Ichtyosis hystrix Hair on the rim of ear Joined 2nd and 3rd toes DNA that is not organized into genes

25 SEX-INFLUENCED TRAITS P: Heterozygous female X heterozygous male Bb X Bb G: 1/2 B, 1/2 b 1/2 B, 1/2 b F1 : Inheritance of pattern baldness in humans ♀ BB Bbbb Bald normal ♂ BB Bb bb Bald normal

26 Other examples of sex- influenced traits include; -Development of mammary glands in human -Coat patterns and milk production in cattle -Egg production in birds

27 NON-DISJUNCTION P: Vermillion- eyed female X red eyed male 6 + X r X r X 6+ X R Y G: 1/1(3+ X r ) 1/2(3+ X R ), 1/2(3+ Y) F1 : 1/2(6 + X R X r ) ; 1/2 (6+ X r Y) R= dominant red-eye gene r = vermillion (recessive) gene

28 P: Vermillion-eyed female X red eyed male 6 + X r X r X 6+ X R Y G: (3+ X r X r ) (3+0) (3+ X R ), (3+ Y) F1 : (6 + X R X r X r ) (6+ X R 0) ; (6+X r X r Y) (6+ Y0) R= dominant red-eye gene r = vermillion (recessive) gene Nondisjunction explains exceptions in the sex–linked inheritance of eye color in Drosophila: nondisjunction ♂ Red (sterile) ♀Vermillicdies

29 Primary nondisjunctionSecondary nondisjunction

30 ANEUPLOIDY: When an organism gains or loses one or more chromosome but not a complete set MONOSOMY The loss of a single chromosome TRISOMY The gain of one chromosome EUPLOIDY: The condition in which complete haploid sets of chromosomes are found. If there are three or more sets, the condition is called polyploidy.(3n, 4n, 5n, 6n, 7n etc.) Egg (n-1) + sperm (n) (2n -1) ex: Turner (XO) Egg (n+1) + sperm (n) (2n + 1) ex: Down Syndrome (45 +XX or 45 + XY)

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33 GENE LINKAGE Genes linked on the same chromosome are generally inherited together; they move together during meiosis (does not obey Mendel’s Principle of Independents Assortment unless crossing over occurs)

34 F1: All purple-flowered and elongated pollen-grained offspring (purple-flowered and elongated pollen grain genes are dominant) P : x Pure purple-flowered and elongated pollen-grained pea plant Pure red-flowered and elongated pollen-grained pea plant PPEEppee P from F1: Dihybrid purple-flowered and elongated pollen-grained parents PpEe X F2: ¾ purple-flowered and elongated pollen-grained offspring : ¼ purple-flowered and elongated pollen-grained offspring

35 Expected phenotypic ratio was 9:3:3:1 But the actual ratio was found to be 3:1 Conclusion: The genes for flower color and pollen grain shape are linked The inheritance of two linked traits produced the same genotype and phenotype ratio in F2 as in monohybrid cross, (1:2:1) and (3:1) respectively. Gene linkage reduces variety

36 P: PPEE x ppee G: PE pe F1: PpEe ( purple elongated pollen *dominant traits) P (from F1): PpEe x PpEe G: ½ PE, ½ pe ½ PE, ½ pe F2: ¼ PPEE, 2/4 PpEe, ¼ ppee are linked PEPE pepe ¾ purple elongated ; ¼ red-round 3:1 phenotypic ratio 1:2:1 genotypic ratio

37 Test cross of F1 P: PpEe X ppeePpEe X ppee G: 1/2 PE, 1/2 pe 1/1 pe ¼ PE, ¼ Pe, ¼ pE, ¼pe X 1/1 pe F1 : 1/2 PpEe ; 1/2 ppee ¼ PpEe; ¼ Ppee; ¼ppEe; ¼ ppee Expected phenotypic ratio: 1:1 Actual phenotypic ratio: 7 : 1 : 1 : 7 Recombinants due to the crossing over Gene linkage

38 CROSSING OVER AND RECOMBINATION

39 Ex: In Drosophila the genes for gray body (G) and normal wing (N) are dominant over the genes for black body (g) and vestigial wing (n) In a Drosophila of genotype GgNn, 12% of the primary sex cells undergo crossing-over. a)What are the types of gametes formed? b)What are the expected percentages of the types of gametes formed?

40 Ex 2: A Drosophila dihybrid forbody color and wing shape (GgNn) is tes crossed and F1 is as follows: Gray – normal : 965Gray – vestigial: 185 Black – vestigial: 944 Black – normail: 206 What is the crossing over value (recombination frequency)?

41 Chromosome Mapping Genes that are close together rarely cross- over Genes that are farther apart will cross-over more often Cross-over studies and cross-over values have been used to construct chromosome maps

42 Ex: Determine the order (sequence) of genes along a chromosome based on the following cross-over (recombination) frequincies. A-B: 8 map units (m.u) A-C: 12 m.uA-D: 25 m.u B-D: 33 m.u D-C: 13 m.uB-C: 20 m.u


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