"In humans, NLGN4 (another gene associated with ASD) is sex-linked, and NLGN4X and NLGN4Y combine to form an X-Y gene pair." "NLGN4X and NLGN4Y are remarkably conserved with only 19 amino acid differences between them." Nguyen TA, Lehr AW, Roche KW. Neuroligins and Neurodevelopmental Disorders: X-Linked Genetics. Front Synaptic Neurosci. 2020 Aug 11;12:33. doi: 10.3389/fnsyn.2020.00033. PMID: 32848696; PMCID: PMC7431521. NLGN4X and NLGN4Y are homologous, in which of the following cases would you expect recombination to occur between them in meiosis? O When X chromosome is activated If they are located in the Pseudoautosomal region of the sex chromosomes O Never O When X chromosome is inactivated

Red–green color blindness is caused by an X-linked recessive genetic defect. Hence females rarely exhibit the red–green colorblind phenotype but may be carriers of the defective gene. When a narrow beam of red or green light is projected onto some areas of the retina of such a female carrier, she can readily diff erentiate the two colors, but on other areas she has diffi culty in doing so. Explain.

Predict the probability (using a Punnett square) of producing an offspring affected by a single gene X-linked mutation given the genotype of the parents. Compare these crosses in two cases: where the mutant allele is “A” vs where the mutant allele is “a” (XAXA x XaY) (XAXa x XAY) (XAXa x XaY) (XaXa x XAY) (XaXa x XaY). Include gender in the phenotype.

Briefly describe the molecular processes that cause one X chromosome in each female cell to be active and the other X chromosome to be inactivated.