Question

A chromosomally XY fetus with normally functioning testes has a mutation in the androgen receptor so it can't respond to testosterone (but it can still respond to MIS). Which of the following WILL develop by the time the child is born?

Select one:

a. A uterus

b. Fallopian tubes

c. A cletoris

d. An epididymis

What important difference appears to explain why some species form pair bonds and others don't?

Select one:

a. Species differences in the size of the nucleus accumbens

b. Species differences in the number and/or distribution of oxytocin and vasopressin receptors in the brain

c. Species differences in the circulating concentrations of oxytocin and vasopressin

Answer 1

1. Androgen receptors allow the body to respond properly to androgen (hormones like testosterone that are important for normal sexual development). Mutation in androgen receptor can result in defect in androgen receptor function, hence will not be able to respond to testosterone.

In females, Mullerian ducts develop into fallopian tubes, the uterus, and parts of female genital tract. In males they are largely reduced. Mullerian inhibiting substance (MIS) causes regression of Mullerian ducts. It is produced in the male embryos.

Since the fetus is able to respond to MIS, fallopian tubes, uterus, and parts of female genital tract will not develop. Option (c) is a part of female genital tract but usually lacks a reproductive function.

Hence, options (a), (b), and (c) are incorrect.

An epididymis is a part of male reproductive system, a tube that holds the testicle in place. Sperm passes along this to the vas deferens. An epididymis can develop in a normally functioning testes and development is independent of testosterone. But maturation and functioning of it depends on the level of testosterone. Thus, an epididymis will develop by the time the child is born.

Therefore, the correct answer is option (d).

2. Pair bond refers to the strong affinity that develops in some species between a pair (a male and a female) leading to the production of offsprings. Some species form pair bonds while others do not.

Nucleus accumbens is a part of the brain and is the reward circuit of the brain. Size of the nucleus accumbens is not critical in forming pair bonds.

Hence, option (a) is incorrect.

Oxytocin and vasopressin are hormones (function as neurotransmitters too) that are important in various processes like sexual behaviors, social recognition and stress response.

Differences in circulating concentrations of oxytocin and vasopressin do not significantly lead to species forming pair bonds.

Hence, option (c) is incorrect.

Distribution of oxytocin and vasopressin receptors in the brain differs in different species. For example, prairie voles are socially monogamous. Males and females form long-term pair bonds. They have significantly greater distribution of oxytocin and vasopressin receptors in the brain compared to polygamous species like montane and meadow voles. Studies have shown that high levels of oxytocin receptor in the nucleus accumbens and high levels of vasopressin receptors in ventral pallidum enables pair bonding in prairie voles.

Therefore, the important difference that explains why some species form pair bonds and others don't is species differences in the number and/or distribution of oxytocin and vasopressin receptors in the brain.

The correct answer is option (b).