Sex-Linked Traits and Colour Blindness

Sex-Linked Traits

• The majority of genes on the X chromosome are not present on the Y chromosome.
• Males only have one copy of most genes on the sex chromosomes.
• Traits coded for on the X chromosome that have no matching counterpart on the Y chromosome are considered sex-linked.
• The gene for normal colour vision is an example and is located only on the X chromosome.
• This gene is dominant, while a recessive variant causes red-green colour blindness.

Colour Blindness Inheritance

• A female with a faulty copy of the colour blindness gene is likely to have normal vision due to the presence of a normal gene on her other X chromosome.
• A female carrying the colour blindness gene can pass the faulty gene to her children, making her a carrier.
• If a male has the abnormal gene, he will be colour-blind due to having only one copy.

Figure 17.11

• Illustrates the potential genetic combinations of children from a carrier mother with one normal and one faulty gene.
• Shows a 50% chance of a son being color-blind and a 50% chance of a son having normal vision.
• Similarly, there is a 50% chance of a daughter being a carrier and a 50% chance of a daughter being normal.

Ageing and Genetics

Ageing and DNA

• The accumulation of mutations in a cell's genome increases with age, which contributes to disease risk, particularly cancer.
• This is due to prolonged exposure to potential mutagens and a decrease in DNA repair mechanisms over time.
• Mitochondrial DNA is more vulnerable to mutations than nuclear DNA and accumulates damage as it ages, impacting cellular function.

Cell Senescence (Ageing)

• Cells have a limited number of divisions, usually between 50 and 60.
• This is attributed to the effects of ageing on telomerase function.
• Telomerase repairs telomeres (chromosome ends) after DNA replication.
• As telomerase function declines, chromosomes shorten progressively, limiting cell division.

Explore the inheritance patterns of sex-linked traits, focusing on the X chromosome and the implications of colour blindness. This quiz covers the differences in gene expression between genders and the roles of carriers in genetic transmission. Test your understanding of how these traits are passed through generations.