Hoi Ki asked in 科學及數學生物學 · 1 decade ago

Genetics

Why are males more likely to be colour blind than females?

(Hint:Colour blindness in a recessive characteristic in humans)

2 Answers

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  • 莫愁
    Lv 6
    1 decade ago
    Favorite Answer

    The genotype of colourblindness can be classified as normal and abnormal ones. For normal gene is XH while for colourblindness gene is Xh and XH is dominant comparing Xh recessive. For male, his sex chromosome is XY while for female her sex chromosome is XX.

    For male, he only has one copy of X chromosome which is said to be hemizygous, medically.[解作:即是只有單一條 X chromosome ]. This hemizygous state makes male to express the colourblindness condition completely if he has the defected gene inherited by her mother. For XHY正常,For XhY中招.

    For female, she has two copies of X chromosomes. This implies if one of the genes is defected(Xh), the other one (XH) will act as a backup and prevents the expression of the colourblindness due to its (normal one's ) dominant nature. XHXH正常, for XHXhY也是正常[因為XH是顯性,而Xh是隱性,所以Xh不會表現出來. ],但是XhXh中招Due to this reason, even a female has a defected gene, it will not be expressed. Hence the chance for a female to suffer from colourblindness will be smaller. This female is just a carrier of the defected gene.

    Colourblindness is said to be sex-linked disease, the same as G-6-PD. Sex linkage disorder means 父親傳了這個缺陷基因給女兒,女兒結婚後把這個缺陷基傳了給兒子.

    I hope you will find them helpful.

  • Anonymous
    1 decade ago

    In the XY sex-determination system, females have two of the same kind of sex chromosome (XX), and are called the homogametic sex. Males have two distinct sex chromosomes (XY), and are called the heterogametic sex.

    The majority of affected individuals are males. Females are carriers, but are not normally affected. This indicates that the X chromosome is one of the locations for color blindness. Male offspring of females who carry the altered gene have a 50-50 chance of being color-blind.

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