Question

least one pathway by genotypically male (XY) could be phenotypically female. 3. If a person is missing all or part of an X chromosome, which syndrome do they have? 4. When does differentiation of the gonads occur embryologically? When does differentiation of the brain occur embryologically? 5. What gene is critical for typical sexual differentiation and where is it found? 6. Draw or describe two pathways by which an individual can develop intermediate or ambiguous genitalia. 7. Can an individual with XX chromosomes develop typical male genitalia? Can they develop typical male gonads? Describe the pathway. 8. What hormone appears to have an important role in sexual differentiation of the brain? 9. What happens to the gonads of most phenotypic females whose chromosomes are atypical? 10. What is Klinefelter syndrome?

Answer 1

2).

Gamete XY XX XY No role Absence of Y and XY Sertoli cells, Anti-Müllerian (7-9th week) Sertoli cells, Anti-Müllerian hormone (AMH), spermatogenesis (7-9th week) ovary - No role on Müllerian system and external genitalia Leydig cells Testosterone Absence of AMH Development accessory organs Development of Müllerian system Testosterone - dihydrosterone (7-8 weeks) Absence of testosterone Male external genitalia (16 weeks) Failed dihydrotestosterone Female external genitalia (14 weeks) Female phenotype (male pseudohermaphrodite) Development of male and female reproductive organs.

3). Turner's Syndrome - either the short arm of X chromosome is deleted or the nucleus possesses only 45 chromosome ie 22 pairs of autosomes plus a sex chromosome XO. .. Mosaicism of XO/XX or even XO/XY produce less clear cut sy drome.

4).
Chronological order of sexual development Time in Weeks Organ Male Female At fertilization XX or absence of Y chromosome induces ovarian development 7-8 weeks 10-12 weeks Genetic determinant (XX or XY) D Gonads are formed Internal and external genitalia XY and SRY antigen in the short arm of Y chromosome induce testicular development Testes seminiferous tubules Wolffian duct develops vas, epididymis, seminal vesicles and external genitalia Ovarian cortex medulla-rete ovarii Müllerian duct develops into fallopian tube, uterus, cervix and upper three-fourths of vagina. External genitalia Appropriate external genitalia Pulsatile secretion of GnRH releases FSH, LH and ovarian hormones At birth Puberty Appropriate external genitalia Continuous GnRH releases testosterone secretion and development of male secondary sex characters Development of secondary sex characters

Fetal sex differences in human brains coupled with early differences in experience may be responsible for sex differences observed in children between 4 years old and adolescence...brain sexual differentiation is generally orchestrated by a surge in gonadal steroid hormones during embryo development followed by a second surge later in adulthood...

5). SRY gene on the short arm(p) of the Y chromosome is the gene invovled in testis determination. At first the germ cells appear followed by sertoli cells that secrete MIF and prevent development of female genital tract. A week later (eighth week) Leydig cells start secreting testosterone by human chorionic gonadotropin hCG and develop accessory organs (Wolfian Duct).

unless SRY is expressed , ovarian development ensues in the presence of XX karyotype . The ovary had no role in the development of Mullerian system and external genital organs.

10). Klienfelter syndrome is seen in 1:500 males. The patient externally resembles a male in general body conformity, the pe*is is small or normal in size. The testes are small but as a rule are normally placed... It karyoptype is 47 XXY.. sterility is common , gynaecomastia is frequently present , the voice is high pitched and apearance maybe eunuchoid. The patient is oftem mentally defective or delinquent..

Sole to pubic length is more than normal. Hyaline degenration of seminiferous tubules seen on testicular biopsy. The person should be bred as male and should not be told about chromosomal abnormality...

note - dear student due to time constraint we have been asked to solve only one question but i have solved quite few... Please repost other question separately.