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Biology 2nd Baccalaureate

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Skip navigation Color blindness or daltonism (problems solved)

Sex-linked inheritance 2. Color blindness. (Page 17)

The color blindness is a genetic defect that causes difficulty distinguishing colors. It is a type of inheritance linked to sex, specifically, to the X chromosome. Women have two X chromosomes while men have one X and one Y chromosome. The genes of the X chromosome can be recessive or dominant, and their expression in women and men is not the same because the genes of the X chromosome are The Y chromosome does not pair exactly with the X genes. X-linked recessive genes are expressed in women only if there are two copies of the gene (one on each X chromosome). However, in males there must only be one copy of an X-linked recessive gene for the trait or disorder to be expressed, so they are much more common in males than females. For example, a woman may unknowingly carry a recessive gene on one of her X chromosomes and pass it on to her son, who will express the trait or disorder.

Simulator: Practice simulating color blind crossovers.

Genetics problem 133

Color blindness is determined by a recessive gene (d) linked to the X chromosome. 

How can they be the descendants of a colorblind man and a normal non-carrier woman?.

Genetics problem 134

Color blindness is determined by a recessive gene (d) linked to the X chromosome. 

How can the descendants of a color-blind man and a non-color-blind woman be the daughter of a color-blind man?

Genetics problem 135

The maternal grandmother of a man has normal vision, his maternal grandfather was color blind, his mother is color blind and his father has normal vision. What type of vision will the man have? Indicate the genotype of all.

Genetics problem 136

A woman of normal vision, whose parents were not color blind, married a color blind man. As a result of this union, they have had a son whose vision is correct and a daughter who is colorblind. Determine the genotype of this woman and her parents.

Genetics problem 137

a) Can a normal child have a color-blind father? And a mother?

b) Can normal parents have a color blind child? And a daughter?

Genetics problem 138

The daltonism depends on a recessive gene (d) (located on the X chromosome). A normal vision woman whose father was color blind marries a normal vision man whose father was also color blind. What type of normal vision can be expected of the offspring?

Genetics problem 139

A colorblind woman asks herself the following question: how is it possible that I am colorblind if my mother and grandmother are not? Propose an explanation for this case. This woman's husband has normal vision, can the couple have colorblind daughters? Reason for the answer.

Genetics problem 140

What will be the possible genotypes of the descendants of a woman carrying the color blindness gene and a man with normal vision? What is the probability that one of your descendants is color blind? If they have daughters, what is the probability that they are color blind? What is the probability of having a descendant with color blindness? Reason for the answers representing the diagrams of the possible crosses.

Genetics problem 141

a) Can a normal man have a color blind mother? And a colorblind father?

b) Can a color blind man have a normal mother?

Genetics problem 142

Color blindness is a recessive character linked to sex. A couple, in which he is normal and she is heterozygous, have a color-blind male child.

a) (0.5 points) What is the probability that the couple has a color blind daughter?

b) (1 point) What is the probability that the couple will have a child with normal vision? Argue your answer.

c) (1 point) Which of the woman's (male) grandparents could not be a source of transmission of the gene for color blindness? Argue your answer.


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