Optimal activation of transcription of the GAL genes in yeast requires the function of two proteins: Gal4p and Gal11p. Elimination of either protein decreases activation of the GAL promoters. However, inactivation of Gal11p has the additional and dramatic effect of cell lethality. Why might elimination of Gal11p have a greater effect than elimination of Gal4p

Gal4p is a transcription factor that targets specific GAL genes, while Gal11p is a core component of the Mediator complex that plays regulatory roles in the expression of many different genes (class II genes) in eukaryotic organisms

Explanation:

The Gal4 transcription factor is one of the most widely studied eukaryotic transcriptional activators capable of activating the expression of galactose-induced genes. Gal4 is well-known to target specific enzymes involved in galactose metabolism: GAL1, GAL7, and GAL10. On the other hand, Gal11p is a key subunit of the evolutionary conserved Mediator complex that binds to the RNA polymerase II (RNAP II) in order to regulate the transcription of class II genes (i.e., genes transcribed by RNAP II).

an individual’s sex (i.e., whether they are a male or female) is determined by the sex chromosomes. most people have two sex chromosomes, one that is inherited from their mother and one that is inherited from their father. typically, females have two x chromosomes (xx) and males have one x chromosome and one y chromosome (xy). conditions caused by changes (“mutations”) in genes located on the x chromosome are considered x-linked.

x-linked recessive inheritance

most x-linked conditions are recessive. this means that in a person with two x chromosomes (most females), both copies of a gene (i.e., one on each x chromosome) must have a change or mutation whereas in a person with one x chromosome (most males), only one copy of a gene must have a mutation. a female with a mutation in one copy of a gene on the x chromosome is said to be a “carrier” for an x-linked condition. a male with a mutation in a gene on the x chromosome is typically affected with the condition. because females have two copies of the x chromosome and males have only one x chromosome, x-linked recessive diseases are more common among males than females. however, x-linked recessive diseases can occur in both males and females.

for x-linked recessive disorders, an unaffected carrier mother who has a mutation in a gene on the x chromosome can transmit either the x chromosome with this mutation or a “normal” x chromosome to her children. if the father is unaffected, none of her daughters will be affected and all of her daughters will be unaffected—since they will inherit at least one normal x chromosome from their father. however, each daughter will have a 50% chance of being an unaffected carrier like her mother and a 50% chance of both x chromosomes being normal.

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".