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Haploid vs. Diploid. This is a crucial concept in genetics. You can remember Diploid is Double of each chromosome. Or, think about the dance floor: it takes two people to execute a dip (diploid = 2), but only one person to hop (haploid = 1).
You may have heard hermaphrodite used to describe humans. This is a different meaning of the word. In humans, it means that they were born with atypical development of the male and/or female genitalia. It does not mean that they have the ability to produce both types of gametes.
Estrus bleeding? Although dogs, cats, and other animals "in-heat" often have a bloody discharge, this is not menstruation. It is a slight amount of bleeding caused by ovulation. It can also be a cue to males that the female is ready. Menstruation discharge is a whole different story.
1) Although 2 single-celled gametes fuse during fertilization, only a single-celled zygote is formed. The sperm provide little more than chromosomes to the egg; therefore, it remains a single cell when they fuse.
2) Maybe you were confused reading that brain snack because you thought that the only cause of male infertility was the inability for sperm to reach the egg (bad swimmers or few swimmers). However, as shown in this video there are sometimes problems with the sperm getting in too. Some clinics can fix this problem by directly injecting the sperm into the egg as shown here.
Embryo phases: Blastocyst is the first hollow stage, so think of it like something that got blasted and hollowed out.
Ovo, ovovivi, and viviparous: Ovo is the egg layer. Vivi is the live birth. Ovovivi is both: eggs carried inside for live birth.