SEX- LINKED INHERITANCE

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

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

CONCLUSION: ALL RED-EYED OFFSPRING P (FROM F1): XR Xr X XR Y P: XR XR X Xr Y G: 1/1 X 1/2 , 1/2 F1: 1/2 X R X r ; 1/2XR Y CONCLUSION: ALL RED-EYED OFFSPRING P (FROM F1): XR Xr X XR Y G: 1/2 XR , 1/2 Xr x 1/2 XR , 1/2 Y F2: 1/4XR XR ; 1/4 XRXr ; 1/4 XR Y ; 1/4 Xr Y * XR Xr Y ¾ RED-EYED ♀ AND ♂ ¼ WHITE-EYED ♂

F1: 1/4XR Xr ; 1/4 XrXr ; 1/4 XR Y ; 1/4 Xr Y TEST CROSS P : XR Xr X Xr Y G: 1/2 XR , 1/2 Xr X 1/2 Xr , 1/2 Y F1: 1/4XR Xr ; 1/4 XrXr ; 1/4 XR Y ; 1/4 Xr Y RED-EYED ♀ WHITE-EYED ♀ RED-EYED ♂ WHITE -EYED ♂ 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

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

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

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

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

DUCHENNE MUSCULAR DYSTROPHY

Normal ♀ color blind♂ carrier♀ XR XR Xr Y XR Xr COLORBLINDNESS Normal ♀ color blind♂ carrier♀ XR XR Xr Y XR Xr Normal ♂ colorblind ♀ XR Y X r Xr

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

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

Ichtyosis hystrix : balık pulluluk

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

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

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

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

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

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

Primary nondisjunction Secondary nondisjunction

The gain of one chromosome MONOSOMY The loss of a single chromosome ANEUPLOIDY: When an organism gains or loses one or more chromosome but not a complete set TRISOMY The gain of one chromosome MONOSOMY The loss of a single chromosome 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) 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.)

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)

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

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

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

P: PpEe X ppee PpEe X ppee Test cross of F1 P: PpEe X ppee PpEe 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 Gene linkage Expected phenotypic ratio: 1:1 Actual phenotypic ratio: 7 : 1 : 1 : 7 Recombinants due to the crossing over

CROSSING OVER AND RECOMBINATION

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. What are the types of gametes formed? What are the expected percentages of the types of gametes formed?

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

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

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.u A-D: 25 m.u B-D: 33 m.u D-C: 13 m.u B-C: 20 m.u