a) Draw a labelled diagram of strands of cell having hereditary characters with nitrogen bases. [2] b) Explain about In vitro fertilization with diagram. [3]

a) Strands of DNA with Hereditary Characters (Nitrogen Bases)

The diagram above illustrates the double-helix structure of DNA, the molecule responsible for carrying hereditary information. Key features include:

• Sugar-phosphate backbone: Composed of alternating deoxyribose sugar and phosphate groups linked by phosphodiester bonds in a 5′ → 3′ direction.
• Nitrogenous bases: Four types of bases form the "rungs" of the ladder:
  • Purines (Adenine (A), Guanine (G)): Two-ring structures.
  • Pyrimidines (Thymine (T), Cytosine (C)): Single-ring structures.
• Base pairing rules:
  • Adenine (A) pairs with Thymine (T) via two hydrogen bonds.
  • Guanine (G) pairs with Cytosine (C) via three hydrogen bonds.
• Hereditary function: The sequence of these bases encodes genetic information (genes) that determines traits.

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b) In-vitro Fertilization (IVF) with Diagram

Explanation of IVF Process

1. Ovulation Induction: Hormone injections (e.g., FSH, LH) stimulate the ovaries to produce multiple eggs.
2. Egg Retrieval: Eggs are collected via a minor surgical procedure (follicle aspiration) under anesthesia.
3. Sperm Collection: Sperm is collected from the male partner or a donor.
4. Fertilization in Lab: Eggs and sperm are combined in a petri dish. If fertilization fails, Intracytoplasmic Sperm Injection (ICSI) may be used.
5. Emryo Development: Fertilized eggs (zygotes) develop into embryos over 3–5 days. Embryos are monitored for quality.
6. Embryo Transfer: One or more healthy embryos are transferred into the uterus using a catheter.
7. Pregnancy Test: A blood test (β-hCG) is conducted 2 weeks post-transfer to confirm pregnancy.

Advantages of IVF:

• Assists couples with infertility due to blocked fallopian tubes, low sperm count, or unexplained infertility.
• Allows genetic screening for hereditary diseases.
• Enables single women or same-sex couples to conceive using donor sperm/eggs.

Limitations:

• High cost and emotional stress.
• Risk of multiple pregnancies (if multiple embryos are transferred).
• Ethical concerns (e.g., disposal of unused embryos).