Human Reproduction

Twins are born to a family that lives next door to you. The twins are a boy and a girl. Which of the following must be true?

1. They were conceived through in vitro fertilization.
2. They have 75\% identical genetic content.
3. They are monozygotic twins.
4. They are fraternal twins.

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). In the light of the above statements, choose the correct answer from the options given below:

1. Both A and R are true but R is NOT the correct explanation of A.
2. A is true but R is false.
3. A is false but R is true.
4. Both A and R are true and R is the correct explanation of A.

Receptors for sperm binding in mammals are present on :

1. Zona pellucida
2. Corona radiata
3. Vitelline membrane
4. Perivitelline space

Meiotic division of the secondary oocyte is completed

1. At the time of fusion of a sperm with an ovum
2. At the time of copulation
3. Prior to ovulation
4. After zygote formation

Extrusion of second polar body from egg nucleus occurs :

1. Before entry of sperm into ovum
2. Simultaneously with first cleavage
3. After entry of sperm but before fertilization
4. After fertilization

Capacitation occurs in

1. epididymis
2. vas deferens
3. female reproductive tract
4. rete testis

Fertilisation in humans is practically feasible only if

1. the ovum and sperms are transported simultaneously to ampullary-isthmic junction of the cervix
2. the sperms are transported into cervix within 48 hrs of release of ovum in uterus
3. the sperms are transported into vagina just after the release of ovum in Fallopian tube
4. the ovum and sperms are transported simultaneously to ampullary-isthmic junction of the Fallopian tube.

Ectopic pregnancies are referred to as

1. implantation of defective embryo in the uterus
2. pregnancies terminated due to hormonal imbalance
3. pregnancies with genetic abnormality
4. implantation of embryo at site other than uterus.

Capacitation refers to changes in the

1. ovum after fertilisation
2. sperm after fertilisation
3. sperm before fertilisation
4. ovum before fertilisation

Identify the human developmental stage shown below as well as the related right place of its occurrence in a normal pregnant woman, and select the right option for the two, together. [Figure]

1. Developmental stage Late morula, Site of occurrence Middle part of Fallopian tube
2. Developmental stage Blastula, Site of occurrence End part of Fallopian tube
3. Developmental stage 8-celled morula, Site of occurrence Starting point of Fallopian tube
4. Developmental stage Blastocyst, Site of occurrence Uterine wall

Which one of the following statements is false in respect of viability of mammalian sperm?

1. Viability of sperm is determined by its motility
2. Sperms must be concentrated in a thick suspension
3. Sperm is viable for only up to 24 hours
4. Survival of sperm depends on the pH of the medium and is more active in alkaline medium

What happens during fertilization in humans after many sperms reach close to the ovum?

1. Only two sperms nearest the ovum penetrate zona pellucida
2. Secretions of acrosome help one sperm enter cytoplasm of ovum through zona pellucida
3. All sperms except the one nearest to the ovum lose their tails
4. Cells of corona radiata trap all the sperms except one.

In human female the blastocyst

1. gets implanted into uterus 3 days after ovulation
2. gets nutrition from uterine endometrial secretion only after implantation
3. gets implanted in endometrium by the trophoblast cells
4. forms placenta even before implantation

The second maturation division of the mammalian ovum occurs

1. Shortly after ovulation before the ovum makes entry into the Fallopian tube
2. Until after the ovum has been penetrated by a sperm
3. Until the nucleus of the sperm has fused with that of the ovum
4. in the Graafian follicle following the first maturation division

Which one of the following statements about morula in humans is correct?

1. It has almost equal quantity of cytoplasm as an uncleaved zygote but much more DNA
2. It has far less cytoplasm as well as less DNA than in an uncleaved zygote
3. It has more or less equal quantity of cytoplasm and DNA as in uncleaved zygote
4. It has more cytoplasm and more DNA than an uncleaved zygote

Grey crescent is the area -

1. Just opposite to the site of entry of sperm into ovum
2. At the point of entry of sperm into ovum
3. At the vegetal pole
4. At the animal pole

What is true for cleavage?

1. Size of embryo decreases
2. Size of embryo increases
3. Size of cells increases
4. Size of cells decreases

Cleavage in mammals is

1. holoblastic equal
2. holoblastic unequal
3. superficial
4. discoidal.