Oxytocin is a hormone found in mammals that is associated with bonding, empathy, and trust. Testosterone is also a hormone, but it is associated with sexual development in males. Dopamine and endorphins are both associated with positive feelings, but they are types of neurotransmitters—a different type of chemical messengers—not hormones. 

"Eating a snack," specifically one filled with carbohydrates would introduce sugar into the body. After being absorbed into the bloodstream, the levels of glucose in the blood would rise to normal blood glucose levels. All other answer choices do not include a resolution to rectify low blood sugar levels. 

The gene for red-green color blindness is on the X chromosome, and the trait is recessive. Females carry two copies of the X chromosome, while males carry only one. The genotypes of the parents must be X^rX^r for the mother and X^RY for the father, with X^r representing the recessive color-blind allele and X^R representing the dominant healthy allele.

The possible genotypes for the children of these two individuals are: X^rX^R, X^rY, X^rX^R, X^rY. 

Any sons must receive the Y chromosome from the father and a color-blind X^r chromosome from the mother, giving them all the genotype X^rY. All of the couple's sons will be color-blind.

Any daughters must receive the dominant healthy X^R chromosome from the father and a color-blind X^r chromosome from the mother, giving the all the genotype X^rX^R. All of the couple's daughters will have normal vision.

The zygote refers to a fertilized egg. At eight weeks, the baby becomes known as an embryo, and fetus refers to the stage of development between 8 weeks and birth. 

Epistasis is when one gene is dependent on the prior function of another. Epistasis can influence the development of many mental disorders.

Our genes have an almost frightening level of influence on how we develop and grow. Genetic influence has been illustrated by many studies focused on twins. Many researchers have found that even when twins were reared in different environments, twins still had significant similarities in personality, intelligence, interests, and behavior. This is not to say that genes are the only factor, they are simply a significant factor in a sea of, nearly infinite, factors influencing development.

"Nature vs. nurture" refers to a long-standing debate about the degree to which our inherited genetic and biological qualities ("nature") or our environment/surroundings ("nurture") influence and shape us. It is generally agreed upon that both influence our behavior in differing ways, but there is still theoretical controversy as to how much each one does. 

The 5-TT gene has been shown to play a role in depression due to its influence on serotonin levels. In a research study, it was found that those with a shorter 5-TT gene were more prone to become depressed after a stressful event compared to those with a longer 5-TT gene. It is difficult to say it is directly linked however, since a strict cause-effect relationship has not been definitively proven, but a strong correlation has been indicated.

A host of family, twin, and adoption studies have shown that all of the disorders provided as answer choices share a hereditary component. Other mental illnesses such as major depression and panic disorder have also shown indications of genetic influence. Genetics will play a role in virtually any disease, but due to the complex nature of the brain and environmental factors, the direct genetic factors influencing psychological disorders are difficult to pinpoint.

Because John's phenotype is brown eyes and brown eyes are dominant, his genotype must be either BB or Bb. However, because we know he carries the gene for blue eyes as well, one of his alleles must be a b (small b). The only genotype that fits these conditions is Bb.