Types of Reproduction: Sexual versus Asexual Reproduction

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00:00:16.05 Although most species on the planet reproduce sexually,
00:00:19.22 why do some species still reproduce asexually?
00:00:22.14 Why is it evolutionarily beneficial
00:00:24.27 for some species to require two parents to produce offspring
00:00:28.07 and others only one?
00:00:30.28 Let's explore why different forms of reproduction exist
00:00:33.22 and what makes each one beneficial
00:00:35.25 in specific circumstances.
00:00:38.24 The two types of reproduction
00:00:40.15 are asexual and sexual.
00:00:42.01 Asexual reproduction is when an organism
00:00:45.14 makes a genetically identical clone of itself.
00:00:48.17 Most of the simplest life forms,
00:00:50.18 such as bacteria,
00:00:52.13 reproduce in this manner.
00:00:54.16 Sexual reproduction is much more complex
00:00:57.21 and involves two members of a species
00:01:00.01 coming together to produce genetically distinct offspring.
00:01:03.25 Most eukaryotic multicellular organisms,
00:01:07.17 such as humans, birds, and insects,
00:01:09.11 undergo sexual reproduction.
00:01:12.12 The biggest advantage of sexual reproduction
00:01:14.14 is that offspring are genetically distinct
00:01:18.03 from their parents and their siblings.
00:01:19.24 This allows a species to evolve,
00:01:22.11 since natural selection will favor the offspring carrying genes
00:01:24.25 that improve their survival in diverse environmental conditions.
00:01:28.16 For example, humans who carry two abnormal copies
00:01:32.07 of the hemoglobin gene
00:01:34.03 develop sickle cell anemia,
00:01:36.01 a devastating disease that results in
00:01:38.21 abnormally low levels of oxygen in the blood.
00:01:41.10 Individuals who have only one copy of the abnormal gene
00:01:44.18 have a much less severe form of the disease.
00:01:47.27 Interestingly, heterozygous individuals
00:01:50.00 are much less prone to infection by malaria,
00:01:52.06 making them more likely to survive
00:01:54.05 and have higher reproductive success
00:01:56.08 in malaria-endemic areas.
00:01:59.09 This example shows how sexual reproduction
00:02:01.14 can produce offspring
00:02:03.14 who are genetically distinct from their parents
00:02:05.15 and are better suited to survive
00:02:07.22 under certain environmental conditions.
00:02:10.02 We have been talking about genetic diversity,
00:02:12.14 but how does sexual reproduction
00:02:14.19 generate this diversity in the first place?
00:02:17.03 During meiosis, which produces the sperm and the egg
00:02:19.29 needed for sexual reproduction,
00:02:22.09 there are two key steps that produce genetic diversity.
00:02:25.11 First is recombination between homologous chromosomes.
00:02:29.09 Recombination mixes maternal and paternal alleles,
00:02:32.07 and results in novel gene combinations
00:02:34.17 on each chromosome in each generation.
00:02:37.18 The second is the independent assortment of chromosomes,
00:02:40.29 which generates unique combinations of chromosomes
00:02:44.11 in each gamete.
00:02:46.20 During fertilization,
00:02:48.24 one genetically unique sperm
00:02:50.26 and one genetically unique egg
00:02:54.02 randomly combine to form an offspring
00:02:56.01 that is genetically distinct from its parents.
00:02:58.01 While genetic diversity arising from sexual reproduction
00:03:01.00 has been critical for the survival of many species,
00:03:04.07 mating is an energy consuming, slow, and risky process.
00:03:08.02 To improve the chance of selecting the best partner,
00:03:11.03 and therefore the best alleles,
00:03:13.04 some species have evolved highly sophisticated courtship behaviors.
00:03:18.10 Male peacocks, for example,
00:03:20.03 grow long, iridescent tail feathers
00:03:22.20 and perform an elaborate dance to attract a mate.
00:03:26.00 But this process requires energy
00:03:27.29 and can attract predators.
00:03:30.01 In addition, the generation of gametes for sexual reproduction,
00:03:33.05 and the subsequent gestation and incubation,
00:03:36.07 take time and energy.
00:03:37.27 For example,
00:03:40.19 emperor penguins must sit on their eggs for over two months,
00:03:43.14 and elephants can be pregnant for almost two years.
00:03:49.02 While asexual reproduction
00:03:51.03 does not produce genetically distinct offspring,
00:03:53.07 it has important advantages
00:03:55.07 that allow for species survival.
00:03:57.11 One, it is energy efficient
00:03:59.15 and does not require attracting a mate.
00:04:02.02 Two, it is usually fast.
00:04:04.10 Some bacteria can reproduce
00:04:06.12 in as little as twenty minutes.
00:04:08.17 And three, it produces offspring that are genetically identical,
00:04:12.14 an advantage in stable environmental conditions.
00:04:16.24 For example, bacteria that carry
00:04:19.04 an ampicillin antibiotic resistance gene
00:04:22.07 will continue to grow in patients prescribed this antibiotic.
00:04:25.16 Conversely, because asexual reproduction
00:04:28.22 results in genetic clones,
00:04:30.20 these bacteria would all die if the patient
00:04:32.20 was treated with a different antibiotic.
00:04:35.26 Rare, random mutations in the genome
00:04:38.13 do allow asexually reproducing organisms
00:04:41.23 to evolve diversity.
00:04:44.17 However, this is a slow process,
00:04:46.27 and there is no mechanism to separate harmful and beneficial mutations
00:04:50.17 for propagation to future generations.
00:04:54.04 Both sexual and asexual reproduction
00:04:56.20 provide important methods
00:04:59.07 for species survival and adaptation,
00:05:01.01 allowing the millions of species on Earth today
00:05:04.00 to evolve and survive in their current forms.
00:05:09.05 This video has been provided to you by Youreka Science
00:05:11.22 and iBiology, bringing the world's best biology to you.

This Talk

Speaker: Youreka Science

Audience:

General Public
Educators of H. School / Intro Undergrad
Student
Educators of Adv. Undergrad / Grad
Researcher

Recorded: August 2017

Talk Overview

There are two types of reproduction: asexual and sexual reproduction. Though asexual reproduction is faster and more energy efficient, sexual reproduction better promotes genetic diversity through new combinations of alleles during meiosis and fertilization. However, as Youreka Sciences explains, both of these types of reproduction can be beneficial to different organisms.

Speaker Bio

Youreka Science

Youreka Science was created by Florie Mar, PhD, while she was a cancer researcher at UCSF. While teaching 5th graders about the structure of a cell, Mar realized the importance of incorporating scientific findings into classroom in an easy-to-understand way. From that she started creating whiteboard drawings that explained recent papers in the scientific literature… Continue Reading