X-Linked Inheritance and Colorblindness

This lecture discusses the genetic concepts of X-linked genes, focusing on the differences in gene expression between males and females due to the presence of defective alleles on the X chromosome. It explains hemizygosity in males, where they have only one copy of X-linked genes, leading to direct phenotype determination by the allele present. The lecture also covers X inactivation in females, which prevents them from being affected by single defective alleles. The session concludes with a problem on colorblindness, exploring its genetic basis and prevalence.

What does the term 'x-linked' refer to?

• Genes located on the Y chromosome

• Genes located on mitochondrial DNA

• Genes located on the X chromosome

• Genes located on autosomes

Why are males considered hemizygous for X-linked genes?

• They have more than two copies of each X-linked gene

• They have no X-linked genes

• They have only one copy of each X-linked gene

• They have two copies of each X-linked gene

What happens when a male inherits a defective allele on the X chromosome?

• The phenotype is determined by the defective allele

• The phenotype is always normal

• The phenotype is unaffected

• The phenotype is determined by the Y chromosome

Why do females generally not suffer from a single defective allele on the X chromosome?

• The defective allele is always recessive

• The defective allele is always dominant

• X inactivation ensures only one allele is active

• They have two defective alleles

How does X inactivation protect females from defective alleles?

• By activating both alleles in all cells

• By ensuring the functional allele is active in some cells

• By deactivating all alleles

• By activating only the defective allele

What is the assumed percentage of X chromosomes carrying the recessive allele for red-green colorblindness?

• 5%

• 10%

• 20%

• 15%

What is the genetic cause of red-green colorblindness?

• Dominant allele on the Y chromosome

• Recessive allele on the X chromosome

• Dominant allele on an autosome

• Recessive allele on the Y chromosome

What is the purpose of the colored images used in the lecture?

• To assess depth perception

• To measure visual acuity

• To screen for colorblindness

• To test for hearing defects

What is the main focus of the problem-solving exercise at the end of the lecture?

• Calculating the number of X chromosomes

• Determining the proportions of colorblind men and women

• Understanding Y-linked inheritance

• Identifying dominant alleles

Why might the colored images not be well controlled for screening?

• Due to variations in monitor colors

• Because they are black and white

• Due to their high resolution

• Because they are too small