Write short notes on any two of the following : (a) Intra-uterine devices (b) Structure of testis (c) Incomplete dominance.

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> [!TLDR]
> IUDs are uterus-inserted contraceptives (Cu-releasing, hormone-releasing or non-medicated) that prevent fertilisation/implantation; incomplete dominance is when the F1 heterozygote is intermediate between the two parents (e.g. pink snapdragon/Mirabilis), giving a 1:2:1 F2 ratio.
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> (a) Intra-uterine devices (IUDs):
> - These are contraceptive devices inserted into the uterus through the vagina by doctors or expert nurses.
> - Types:
>   1. Non-medicated IUDs — e.g. Lippes loop.
>   2. Copper-releasing IUDs — e.g. CuT, Cu7, Multiload 375. The released Cu ions suppress sperm motility and the fertilising capacity of sperms.
>   3. Hormone-releasing IUDs — e.g. Progestasert, LNG-20. These make the uterus unsuitable for implantation and the cervix hostile to sperms.
> - IUDs increase phagocytosis of sperms within the uterus and, in general, make the uterus unsuitable for implantation.
> - They are ideal contraceptives for females who want to delay pregnancy/space children; they are one of the most widely used, reversible methods in India.
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> (c) Incomplete dominance:
> - It is a pattern of inheritance in which one allele is not completely dominant over the other, so the heterozygous F1 shows a phenotype that is intermediate between the two homozygous parents.
> - Example: In the flower Mirabilis jalapa (four o'clock plant) / snapdragon (Antirrhinum), a cross between a red-flowered plant (RR) and a white-flowered plant (rr) gives F1 plants with pink flowers (Rr) — intermediate, not red.
> - On selfing the F1, the F2 shows red : pink : white in the ratio 1 : 2 : 1. Here the phenotypic ratio is the same as the genotypic ratio (1:2:1), because each genotype has its own distinct phenotype.
> - This showed that the dominance of one allele over another is not always complete.
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Q.Write short notes on any two of the following :

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