Question

Suppose a graduate student is studying a loss-of-function mutation in the mouse gene zigzag. whereas wild type mice have straight tails, zigzag mutant mice have tails with two sharp kinks, so that the tail looks like the letter z. to determine how the zigzag phenotype is inherited, he performs the crosses listed in the first colu

Answer 1

Complete question:

Suppose a graduate student is studying a loss-of-function mutation in the mouse gene zigzag. Whereas wild type mice have straight tails, zigzag mutant mice have tails with two sharp kinks, so that the tail looks like the letter Z. To determine how the zigzag phenotype is inherited, he performs the crosses listed in the first column of the table below, using parents from true-breeding lines. Three possible sets of results from these crosses are shown. Determine the mode of inheritance of the zigzag gene that would yield each result set.

Mode of inheritance Options:

• cytoplasmic-linked recessive inheritance,  

• maternal effect inheritance,

• genomic imprinting (paternal allele is inactive),

• genomic imprinting (maternal allele is inactive),

• x-linked recessive inheritance

Note: You will find the table in the attached file

Answer:

• Set A: X-linked recessive inheritance

• Set B: maternal effect inheritance
• Set C: genomic imprint (paternal allele is inactive)

Explanation:

SET A:

X-linked recessive inheritance: This pattern refers to a recessive mutated allele that expresses the abnormal character and is linked to the X chromosome.  

• Cross 1: zig zag female   x   wild type male

Parental) Xz Xz     x    X+Y

F1) Phenotype---> 50% zigzag (all males)   ;  50% wild type (all females)    

      Genotype---> ½ X+ Xz   ;   ½ Xz Y      

• Cross 2:  

Parental) X+ Xz     x   Xz Y    

F1) Phenotype---> From the whole progeny: 25% wild type females ; 25% wild type males ; 25% zigzag females ; 25% zigzag males - 50% wild type animals + 50% zigzag animals

     Genotype---> ¼ Xx Xz  ; ¼  Xx Y ;   ¼ Xz Xz  ; ¼  Xz Y      

• Cross 3: wild type female   x   zigzag male

Parental) X+ X+     x    XzY

F1) Phenotype---> 100% wild type animals (50% females + 50% males)

      Genotype --->  ½ X+ Xz   ;   ½ X+ Y      

• Cross 4:

Parentals) X+ Xz     x    X+Y

F1) Phenotype---> From the whole progeny: 50% wild type females ;  25% wild type males ; 25% zigzag males

      Genotype --->  ¼ X+ X+ ; ¼  X+ Xz   ;  ¼ X+ Y  ;  ¼  Xz  Y

SET B:

Maternal effect: Refers to the influence of the “environment provided by the mother” on the progeny phenotype. The mother´s genotype directly determines the progeny phenotype. The progeny genotype is irrelevant, as well as the father´s genotype or phenotype. This means that no matter what is the genotype of the offspring, all of them will express the same phenotype as their mother. This effect is commonly seen in insects, but it might also occur in mammals and plants. A much known experiment about this effect is the one performed on Limnea sp snail.  

• Cross 1: zig zag female   x   wild type male

Parental) Xz Xz     x    X+Y

F1) Phenotype-->100% zigzag animals, due to the female´s phenotype, Xz Xz      

      Genotype--> ½ X+ Xz   ;   ½ Xz Y      

• Cross 2:  

Parental) Xx Xz     x   Xz Y    

F1) Phenotype-->100% wild type animals, due to the female´s phenotype, Xx Xz      

     Genotype--> ¼ Xx Xz  ; ¼  Xx Y ;   ¼ Xz Xz  ; ¼  Xz Y      

• Cross 3: wild type female   x   zigzag male

Parental) X+ X+     x    XzY

F1) Phenotype-->100% wild type animals, due to the female´s phenotype, X+X+      

      Genotype --> ½ X+ Xz   ;   ½ X+ Y      

• Cross 4:

Parentals) X+ Xz     x    X+Y

F1) Phenotype-->100% wild type animals, due to the female´s phenotype, X+ Xz      

      Genotype---> 100% wild type animals      

SET C:

Genomic imprint (Paternal allele inactive): Refers to a pattern that characterizes for epigenetically inheritance and for unequally functional paternal and maternal genomes. Males X chromosomes are inactive or imprinted and have a different function from those females X chromosomes. This is a common pattern in some mammals, insects and angiosperms. The paternal allele can not be expressed which causes an unequal contribution to the progeny phenotype.  

• Cross 1: zig zag female   x   wild type male

Parental) Xz Xz     x    X+Y

F1) Phenotype--->100% zigzag animals, because the male´s X chromosome is imprinted or inactive      

      Genotype--->½ X+ Xz   ;   ½ Xz Y      

• Cross 2:  

Parental) Xx Xz     x   Xz Y    

F1) Phenotype--->50% wild type animals ; 50% zigzag animals.  Due to both the female´s chromosomes, Xx Xz      

     Genotype---> ¼ Xx Xz  ; ¼  Xx Y ;   ¼ Xz Xz  ; ¼  Xz Y      

• Cross 3: wild type female   x   zigzag male

Parental) X+ X+     x    XzY

F1) Phenotype--->100% wild type animals, due to the female´s phenotype, X+X+      

      Genotype ---> ½ X+ Xz   ;   ½ X+ Y      

• Cross 4:

Parentals) X+ Xz     x    X+Y

F1) Phenotype--->50% wild type animals ; 50% zigzag animals

      Genotype ---> ¼ X+ X+ ;  X+ Y  (Wild type)  

                            ¼  X+ Xz   ;  ¼ Xz Y  ( zigzag)