XX SexLinked Inheritance XY Autosomal chromosomes Chromosome pairs
- Slides: 9
XX Sex-Linked Inheritance XY
Autosomal chromosomes • Chromosome pairs 1 to 22 • Responsible for determining nonsexual characteristics (e. g. eye and hair colour)
Sex chromosomes • The 23 rd pair of chromosomes • Responsible for determining sex (male or female) and sex-related traits (e. g. facial hair)
Sex-linked Inheritance • Many nonsexual traits appear to be inherited along with sex (are more common in one sex than in the other). • Why are some traits more common in one sex vs the other? • Y chromosome is small most gene locations determine sexual characteristics
Sex-linked Inheritance con’t • X chromosome is larger • Nearly 100 genes that control nonsexual characteristics • For example: the X chromosome carries the gene for colour-blindness • B = normal vision b = colour-blind • XBXB = female with normal colour vision • XBXb = female who carries gene for colour-blindness (but has normal colour vision) • Xb. Xb = colour-blind female • XBY = male with normal colour vision • Xb. Y = colour-blind male
Practice Questions 1. A woman who carries the gene for colour-blindness has a child with a man who has normal colour vision. What are the possible genotpyes and phenotypes of their child? 25% female with normal colour vision XB Xb XB XB Xb Y XB Y Xb. Y 25% female with normal colour vision (carrier for colour-blindness) 25% colour-blind male 25% male with normal colour vision
2. A colour-blind man has children with a woman who has normal colour vision (and no history of colour-blindness in her family). What is the possibility that their children will be colour-blind? XB XB Xb Y XB Y There is a 0% chance that their children will be colour-blind. However, their daughters will be carriers of colourblindness.
3. A man and his wife have normal vision, but the daughter is colour-blind. The man sues his wife for divorce on grounds of infidelity. You are his lawyer. What evidence will you provide to the judge? XB Xb XB XB Xb Y XB Y Xb. Y Even if mother was a carrier of colour-blindness, there is a 0% chance of having a colour-blind daughter if the father is not colour-blind.
