Human Reproduction Set-6

Q1. During an IVF cycle two blastocysts are transferred and the implantation probability for each transferred blastocyst is $p=0.35$, independent of the other. What is the probability that at least one embryo implants?

Q2. In an IVF cycle Woman A (age 30) produced $n_A=4$ oocytes with probability $p_A=0.5$ that any one embryo is euploid. Woman B (age 40) produced $n_B=6$ oocytes with probability $p_B=0.2$ that any one embryo is euploid. Assuming independence, the probability a woman has at least one euploid embryo is $P=1-(1-p)^n$. Which of the following gives the correct probabilities (A then B)?

Q3. An ovulation induction protocol results in single ovulation with probability $0.6$ and double ovulation (two oocytes released) with probability $0.4$. Each released oocyte implants independently with probability $0.25$. What is the probability that the cycle results in dizygotic (fraternal) twins (i.e., two oocytes released and both implant)?

Q4. Assertion (A): Among pregnancies that occur with an intrauterine device (IUD) in place, the proportion of ectopic implantations is higher compared to pregnancies in women without an IUD. Reason (R): IUDs act mainly by preventing implantation in the uterine endometrium and do not significantly reduce fertilization in the fallopian tubes.

Q5. Which of the following correctly describes effects of increased parental age on genetic risks to offspring?
Statements:
I. Increased maternal age is strongly associated with higher risk of chromosomal nondisjunction (e.g., trisomy 21).
II. Increased paternal age is primarily associated with higher rates of de novo single-nucleotide (point) mutations in offspring.
III. Increased paternal age substantially increases transmission of mitochondrial DNA mutations to offspring.
IV. Both increased maternal and paternal age equally increase risk of meiotic nondisjunction.

Q6. A woman has a regular menstrual cycle of 31 days. If her luteal phase is consistently 14 days long, on which day of the cycle is ovulation most likely to occur? (Use ovulation day ≈ cycle length − luteal phase, $C - L$, where $C=31$ and $L=14$)

Q7. A couple undergoes assisted reproduction. Semen analysis shows sperm count = 60 million/ml but only 2% progressive motility and many immotile but morphologically intact sperm. Which ART procedure is most appropriate to maximize chance of fertilization?

Q8. Both partners are heterozygous carriers (genotype Aa) of the same autosomal recessive disorder. They plan IVF with preimplantation genetic diagnosis and will implant only embryos that are homozygous normal (AA). If 5 independent embryos are produced, what is the probability that at least one embryo will be homozygous normal? (Use Mendelian probabilities.)

Q9. An anabolic steroid–using male athlete has been self-administering high-dose testosterone for several months. He now has reduced testicular size and semen analysis shows azoospermia, yet serum testosterone remains high. Which mechanism best explains his azoospermia?

Q10. For a normally fertile couple the probability of conception from a single act of intercourse during the fertile window is ~20% (0.20). If they have intercourse on five consecutive days during the fertile window and each act is assumed independent with probability $0.20$ of fertilization, what is the probability that they achieve pregnancy in that cycle?

Q11. A man's ejaculate has volume $2.5\ \mathrm{ml}$, sperm concentration $80\times10^{6}\ \mathrm{ml^{-1}}$ and motile fraction $60\%$. Using $N=V\times C\times f$, the approximate number of motile spermatozoa in the ejaculate is:

Q12. A couple seeks assisted reproduction. Investigations reveal the woman has bilateral tubal blockage (hydrosalpinx) and the man has severe oligozoospermia with total sperm count $\approx 5\times10^{6}\ \mathrm{ml^{-1}}$. Which single technique is most appropriate to maximise chance of fertilisation?

Q13. Assertion (A): A loss‑of‑function mutation in the LH/hCG receptor on luteal cells will most likely cause failure of early pregnancy despite normal embryonic hCG secretion. Reason (R): hCG acts via LH receptors on the corpus luteum to sustain progesterone production until placental steroidogenesis takes over at about $7$–$9\ \text{weeks}$ of gestation.

Q14. Assertion (A): Monochorionic diamniotic monozygotic twins result when the zygote splits between days $4$ and $8$ after fertilisation. Reason (R): The trophoblast (which forms the chorion) differentiates earlier than the amnion, so splitting after chorion formation but before amnion formation yields one chorion but two amniotic sacs.

Q15. A Rh‑negative mother who is already sensitised (has circulating anti‑D IgG) conceives with a man heterozygous for the Rh D antigen (genotype $D d$). Assuming no other modifiers, the probability that the fetus will be Rh‑positive and therefore at risk of haemolytic disease of the newborn is: