University:
University of Virginia
Course:
BIOL 2200 | Introduction to Biology II: Organisms & Evolution
Academic year:

2023
Views:

402

Pages:

4
Author:

Zoe C.

Lecture 6: How Species Are Formed (1/29) balancing selection • maintains multiple forms of alleles • heterozygote advantage heterozygotes have greater • fitness than either homozygote • frequency-dependent selection • sickle cell alleles fitness depends on how common the phenotype is in the population constraints on evolution • laws of physics, thermodynamics, gravity • sources of genetic variation • adaptation is opportunistic • trade-offs • environmental change what is a species? • biological species concept: groups of actually or potentially interbreeding populations, which are reproductively isolated from other groups (mayr 1942) difficulties in defining species • local variation • asexual reproducers • hybrids prezygotic reproductive isolation • habitat isolation: species mate in different places • temporal isolation: species mate at different times • behavioral isolation: unique behaviors attract different species • mechanical isolation: morphological differences prevent mating • gametic isolation: sperm cannot fertilize eggs postzygotic reproductive isolation • reduced hybrid viability: hybrids do not live to maturity • reduced hybrid fertility: hybrids do not produce viable offspring • hybrid breakdown: offspring viability is reduced after several generations allopatric speciation sympatric speciation sympatric speciation: autopolyploidy • cell division error within a species leads to increase in chromosome number • in a diploid, error leads to diploid gametes and tetraploid species • new species likely established through self-fertilization sympatric speciation: allopolyploidy • hybridization between species, chromosomes cannot pair up • error doubles chromosomes, hybrids can now interbreed • new species likely established through self-fertilization • functionally diploid: two unpaired sets of chromosomes and one unpaired chromosome • functionally tetraploid with two sets of paired chromosomes polyploidy is > 2 sets of chromosomes