Morgan's Experiment
Morgan's Experiment
Morgan was a geneticist .He was particularly interested how traits are inherited to offspring.He took a mutant male and bred with wild female.The resulting members of F1 generation all had red-eyes,but morgan suspected that white-eye trait is present in F1 generation,but remains unexpressed,like a recessive trait.He then crossed male and female of F1 generation and the get the resulting members of F2 with ratio 3:1 means one white eyed and three red eyed.
Morgan was curious that the why females never show white-eye trait,he predicted that white eye trait were lethal in females, he conducted a test cross of heterozygous F1 female and crossed with F2 male,and was surprised to see the ratio of 1:1:1:1 means red eyed ♀ ♂ and white eyed ♀ ♂,from this morgan comes to the conclusion:
The white eyed trait is expressed when F1♀ are bred with F2 ♂.
The appearance of the white eyed trait is not lethal in females.
Morgan's Test Crosses
* X+ = Red-eye trait (wild type)
* Xw = White-eye trait
In his first cross in which he wanted to explore relationship between eye color and sex.He crosses white eyed male with red eyed female,and the resulting generation had all red eyes as shown in fig(1).
Morgan's First Test Cross.
In his second test cross he bred a red eyed ♂ with red eyed ♀ from F1 generation and have resulting members of ratio 3:1 as shown in fig(2)
Morgan's Second Test Cross.
Morgan conducted the third cross to check that white eyed trait were lethal in females or not?He bred red eyed ♀ (X+ Xw) with white eyed ♂ (Xw Y) as shown in fig(3)
Morgan's Third Test Cross.
The third cross revealed that the white eyed trait were not lethal in females because it yielded a ratio of 1:1:1:1.
Finally,morgan conducted his fourth test cross to check wether the white eyed trait follow the inheritance of X-chromosomes from female gametes to male offspring.By this cross Morgan could predict that the white eyed female would be homozygous recessive.Because the male only inherit X-chromosome from the mother,so by crossing white eyed ♀(homozygous recessive) with red eyed ♂ shows that X-linked white eyed trait that male offspring carry from that Homozygous recessive mother.Thus, Morgan could predict that all ♂ offspring resulting from a cross between a white-eyed ♀ and a red-eyed ♂ would be white eyed.Likewise,because ♀ carry on X-chromosome from her father gametes,so all females from this cross(4rth) will carry red -eyed trait,and this trait dominate the recessive trait from female gametes.Morgan crossed a White eyed ♀with the red eyed ♂ as shown in fig(4)
Morgan's Fourth Test Cross.
This cross yielded all white-eyed ♂ and all red-eyed ♀ , Morgan could indeed conclude that the white-eye trait followed a sex-linked pattern of inheritance.
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