Month: October 2018

Weekly Reflection #5

On By patrickledouxbiologyIn Uncategorized

This week we moved on from Hardy-Weinberg and focused on the process of speciation. Speciation can be defined as “reproductive isolation,” or the inability of two populations of organisms to interbreed and/or produce fertile offspring. But what would cause a population to split? And what would cause these groups to become so different they can no longer interbreed?

There are several ways this can happen. These fall into two general types of speciation: Allopatric and Sympatric speciation.

Image result for allopatric vs sympatric

In Allopatric speciation, two populations of the same species become physically separated, usually by geographic means. This can include a river, canyon, mountain range, separating continents, etc. This is the more common type of speciation.

In Sympatric speciation, two distinct groups emerge within a population without a physical/geographic barrier between them. This type of speciation is more complicated and less common.

We also learned about the barriers of species, aka the reasons why a giraffe doesn’t mate with a pine tree. These include pre-zygotic (before fertilization) and post-zygotic (after fertilization) barriers. Mechanical isolation and gametic isolation are prezygotic because they make is mechanically impossible for organisms to mate, and for the sperm to fertilize an egg. Habitat isolation, temporal isolation and behavioral isolation are also prezygotic as they prevent organisms from even trying to mate. Postzygotic barriers include hybrid viability, reduced hybrid fertility and hybrid breakdown. These make hybrid offspring of two species either die during birth or are so unsuited to their environment they die anyways. Hybrid Breakdown indicates that the first generation of hybrid offspring are perfectly fine and viable, however after 2 or more generations severe problems begin to arise.

 

Image result for prezygotic vs postzygotic species barriers

Questions Going Forward:

Will these species barriers relate to HWE in any way? How often do hybrid offspring become their own species? How many of the earth’s species are a product of hybrid reproduction?

Weekly Reflection #4 – HWE

On By patrickledouxbiologyIn Big Idea 1

This week’s focus was all Hardy-Weinberg Equilibrium.

Image result for hardy-weinberg equilibrium

We learned the history behind the HWEQ equation, who discovered it, and how to properly use it. We also focused on the conditions necessary for HWEQ. We started out with defining some terms as they relate to Hardy-Weinberg:

  • Gene-  DNA that determines a trait
  • Allele – A variant of a trait (DNA)
  • Dominant Allele – Shows a trait/phenotype, regardless of the other allele.
  • Recessive Allele – An allele that only shows when paired with another recessive.
  • Homozygous – A matching allele pair (PP, dd, hh, KK, etc.)
  • Heterozygous – An unmatched allele pair (Pp, Dd, Hh, Kk, etc.)
  • Evolution – Change in allele frequencies over time.
  • Population – a localized group of interbreeding individuals.
  • Gene Pool – The collection of all the alleles present in a population.
  • Mutation – Creates variation/ new and novel traits. Always happening.
  • Gene Flow – Movement of organisms into/out of a population, changes allele frequencies.
  • Non-Random Mating – Causes sexual selection and sexual dimorphism.
  • Genetic Drift – Random, chance events that change the gene pool.

After learning these terms, we went over the conditions necessary for a population to in HWE, listed below.

  1. Random Mating
  2. No Mutations
  3. No Gene Flow
  4. No Natural Selection
  5. No Genetic Drift

As you can see, very few real-world populations are actually in HWE. What is the purpose of HWE then, if it fails to describe reality? This was an important question this week. Turns out HWE is best used as a null model- a control group.  If you calculate the allele frequencies for a population if it stopped evolving and changing altogether, you can then see how that population has evolved over time compared to the null model. We did a lab to try this technique out on Friday to see if we could achieve HWEQ amongst ourselves. No surprises, we couldnt.

HWE Equation: p^2 + 2pq + Q^2 = 1,     p + q = 1

Synthesis/Questions Going Forward

HWE seems to pull together everything we’ve been learning the past few weeks. It brings all the vocab and methods of evolution and types of alleles into play. This feels like the first relatively powerful tool we’ve received, akin to M1V1 = M2V2 in Chemistry. But how will we better mathematically describe populations and allele frequencies in the future? How will we better simulate reality? Are there ways to account for the things HWE must hold constant?

Big Idea #1

Image result for six fingered amish

 ^ Polydactyly ^

 

 

 

Weekly Reflection #3

On By patrickledouxbiologyIn Big Idea 1

9/23 – 9/28

This week we covered many topics related to evidence for evolution. We began by defining several terms, as to avoid confusion with the way they are used in common speaking.

  • Falsifiability: the idea that scientific thoughts can never be 100% proven, only supported by evidence.
  • Hypothesis: A testable Statement
  • Theory: A major unifying framework supported by all evidence currently known.
  • Law: A deduced fact that will always hold true.

We then discussed the names for the various structures used in comparative anatomy that suggest evolution. Comparative anatomy is a method of deducing organism’s evolutionary relationships by comparing similar structures in their bodies.Image result for comparative anatomy structures

  • Homologous Structures: similar structures in related organisms that serve independent purposes. These suggest that organisms share a common ancestor that had this structure.

 

  • Image result for comparative anatomy structures Structures: Similar adaptations to similar situations and problems (these serve as evidence for convergent evolution)
  • Vestigial Structures: Structures that no longer serve any or very little function, but don’t cause the organism to be selected against (Like the human appendix or the pelvic bones and femurs of whales).

Another topic we covered was the development of phylogenetic (or evolutionary) trees. We learned how modern DNA sequencing results have helped scientists build more expansive and accurate trees, as comparing DNA sequences can reveal evolutionary histories often better than comparative anatomy.Image result for phylogenetic tree

Ongoing Questions:

How is DNA actually collected and read? Can we recreate synthetic DNA? If so, could we design our own synthetic organism? Would that organism be in its own synthetic domain?

HHMI Activity Link: https://www.hhmi.org/biointeractive/creating-phylogenetic-trees-dna-sequences