Evolutionary Biology: Speciation, Reproductive Isolation, and Hybrids

In this video, I explain speciation, the process by which one lineage splits into two independent lineages that evolve separately. For speciation to occur, reproductive isolation is required, which can result from physical barriers (like geographic separation) or genetic incompatibilities. Hybrids are offspring of two different species, such as a mule or hinny, which are crosses between a horse and a donkey. Hybrids are often selected against, either due to reduced viability or infertility (mules and hinnies typically have 63 chromosomes—a mix of 64 from the horse and 62 from the donkey—leading to infertility in most cases). When reproductive isolation between two closely related species is incomplete, a hybrid zone can form. Over time, this zone may disappear, the two species may merge, or the hybrid zone can remain stable.

Time stamps:

- Speciation splits one lineage into two independent lineages: 0:00
- Bateson-Dobzhansky-Muller model for incompatibilities between genes: 3:04
- Hybrid incompatibility occurs in most hybrids of different species and can't reproduce: 5:12
- Figure showing mutations occuring in isolated populations: 7:26
- Comparison of allopatric, peripatric, parapatric, and sympatric speciation: 11:16
- Allopatric speciation: physical barrier.
- Peripatric speciation: much smaller isolated peripheral population: 13:00
- Parapatric speciation: two subpopulations evolve reproductive isolation while continuing to exchange genes: 13:54
- Sympatric speciation: genetic polymorphism or 2+ different morphs or forms in the population: 14:15
- Pre-zygotic isolation occurs before fertilization or mating: 15:17
- Post-zygotic isolation occurs after fertilization or mating and can select against hybridization: 18:52
- Mules and hinnies have 63 chromosomes, a mixture of 64 from horse and 62 from donkey: 19:32
- Mule = male donkey (jack) + female horse (mare)
- Hinnie = male horse (stallion) + female donkey (jenny)
- Hybrid zone is where interbreeding species or diverged lineages meet and cross-fertilize: 21:15
- Possible outcomes of hybrid zones: reinforcement, fusion, or stability: 24:41

Full video below:

- Full video and playlist: https://www.youtube.com/playlist?list=PLai3U8-WIK0FYO6bxFbBAtVJ9sDOJnH72
- Notes: https://peakd.com/hive-128780/@mes/messcience-3-overview-of-biology
- MES Science playlist: https://www.youtube.com/playlist?list=PLai3U8-WIK0FjJpwnxwdrOR7L8Ul8VZoZ .

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