Question

1. Describe the phenotype of an individual with the following condition: XY chromosomes, mother exposed to large amounts of a DHT receptor antagonist during critical window of sex development in pregnancy. Include: gametes, internal genitalia, and external genitalia

2. Describe a mechanism that could cause an individual to develop testes, external male genitalia, and both internal female and internal male genitalia.

Answer 1

Answer of Part I:

sex-determination in the developing fetus follows these steps:

1. Initially, the internal genitalia in the male and female fetus is the same
2. The presence of the Y chromosome is important for the development of the male gender
3. The SRY gene on the Y chromosome releases the testis-determining factor.
4. This causes the gonadal ridge to develop into a testis
5. The testis starts secreting 2 hormones
   1. testosterone (secreted by the Leydig cells)
   2. anti -Mullerian hormone (Secreted by the Sertoli cells)
6. Testosterone promotes the development of the structures of the Wolffian duct
   1. Epididymis
   2. Vas deferes
   3. Ejaculatory duct
   4. Seminal vesciles
7. The anti -Mullerian hormones - causes regression of the mullerian duct. This prevents the development of female reporductive organs

Phenotype:

1. low muscle mass
2. chest like a female breast (gynecomastia)
3. lack of hoarseness in the voice
4. lack of facial hair
5. Lack of development of secondary sexual characters
6. Gametes - produced by this individual will be X and Y ( however, the sperm count may be low due to underdevelop testis)
7. Internal genitalia - the absence of Mullerian duct structure like fallopian tube, uterus
   • Explanation - the fetal testes will produce 2 hormones
     • testosterone
     • anti -Mullerian hormone
   • The anti-mullerian hormone will cause the regression of the Mullerian duct
   • This will prevent fallopian tube, uterus from forming
   • The anti-mullerian hormone is not affected by the DHT (dihydrotestosterone) receptor antagonist
   • Structures like Epididymis, Vas deferen, Ejaculatory duct may be underdeveloped
8. External genitalia
   • there will be a feminization of the male external genitalia
   • The anorectal distance is reduced.
   • ambiguous external genitalia
   • This individual will have testes( may be hypofunctional and undescended). As the chromosomes are XY

Answer Part II

The mechanism behind the development of both male and female internal and external genitalia in the same individual are

1. An ovum may split into two. the two ova get fertilized by 2 different spermatozoa (one X and other Y). so there are 2 zygotes ( one is XY and other XX). These zygotes may later fuse
2. One ovum fertilized by 2 spermatozoa (one X other Y)
3. Two ova may get fertilized with 2 different spermatozoa (one X and other Y). This would lead to the formation of 2 zygotes (XX, XY). These may fuse with each other.
4. Mutation in the SRY gene