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Biology 2nd Baccalaureate

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Heredity linked to sex. Problems solved. (Page 21)

Genetics problem 157

Starfish are the main predators of mussels and can potentially cause economic losses to producers of this mollusk. To combat possible star plagues, the controlled introduction of dwarf stars, with short arms, without the force to open the mussels, a character due to a recessive allele linked to sex (Xe), is being studied. The dominant allele (XE) has no effect on animals (wild type).

a. In a first phase of the process, carried out in the laboratory, thousands of homozygous wild star eggs were fertilized with sperm from dwarf males. What phenotypes were obtained between F1 males and females?

b. At a later stage, female eggs obtained in F1 were fertilized with sperm from dwarf males. What proportion of the males of this F2 are still wild?

Genetics problem 158

After several attempts, a new variety of pangolin was obtained in a laboratory. When crossing a normal female with a snout male, all the normal males and all the snout females came out. Subsequently, the F2 was carried out and it was found that half of the males and half of the females were snout. Try to explain these results.

Genetics problem 159

A female Drosophila of unknown genotype regarding eye color is crossed with a male with white eyes (W). The white color of the eyes is an X-linked character and recessive with respect to the wild red eye color (W+). In the obtained offspring, half of the males and half of the females belong to the red eyes phenotype and half of the males and half of the females belong to the white eyes phenotype. Reasonably deduce:

a) What is the genotype and phenotype of the parental female Drosophila? 

b) What are the genotypes of the possible individuals of the filial F1 generation obtained from the indicated cross? Represents the crossover

Genetics problem 160

Duchenne muscular dystrophy is a genetic disease that mainly affects children. The disease is caused by the mutation of a gene located on the X chromosome, which codes for dystrophin, a fundamental protein for the structural and mechanical maintenance of the muscle fiber.

A woman, whose male child is born with this disease, sues the chemical company where she works claiming that no member of her family or that of her partner (neither man nor woman) has suffered from the disease in generations and, therefore Therefore, the chemical compounds to which it has been exposed for years have caused the mutation in the fetus.

Is the family right? Justify it genetically.


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