Studied by 1 person
Continuous Variation
-No distinct classes or categories
-Shows a “normal distribution” and results cluster around an average value
-Range between 2 extremes
Discontinuous Variation
-Discrete with distinct categories
-Does not show “normal distribution”
-No immediate form
Species
A group of organisms with shared traits
Morphology
Naming and classifying by describing the outer form and inner structure of typical members of species
Morphological Species Concept
Idea of a species as a group of organisms that share a particular outer form and inner structure
Advantages of morphological species concept
Can be applied to asexual or sexual organism
Does not require any information on the extent of gene flow
Can be applied to extinct and fossilized species
Easiest and fastest concept to apply in the field
Disadvantages of morphological species concept
relies on subjective criteria and researchers may disagree on which structural features distinguish a species
Different individuals in a species may appear very different
Biological Species Concept
Defines a species as a group of organisms that can successfully interbreed and produce fertile offsprings
Advantages to BSC
There are more opportunities for breeding and evolving
Limitations to the biological species concept
-Does not apply to organisms that reproduce asexually
-Does not apply to organism that are extinct
-Does not apply to organisms that freely hybridized
Hybridization
Hybridization of two species suggest that those species are not distinct
Very difficult to apply when organism are geographically separated
Chromosomes in humans
Have 23 types of chromosomes (46 total) (22 autosomes + 1 sex chromosome)
Chromosomes
Each type of chromosome carries specific genes which occupies a specific locus on that chromosome
Homologous chromosomes
Two chromosomes with genes in the same loci
Same shape and size
Form homologous pairs
Haploid and Diploid
Haploid: (n) (Humans: n = 23)
Have 1 chromosome of each type
Have one full set of chromosomes
Diploid: (2n) (Humans: 2n = 46)
2 copies of each type of chromosome
2 full sets
Chromosome 2
Hypothesis that it was formed from the fusion of chromosomes 12 and 13 from a shared primate ancestor
Our closest relatives have diploid # of 48 while we have 46
<3% of human DNA is different from chimps
Genomes
All genetic info of 1 individual organism or group of organisms
The entire base sequence of each DNA molecules
Alleles
Alternate versions of a gene, which often exist within a species
Each allele codes for a different variation of a specific trait
As alleles are alternate forms of the same gene, they have the same locus
Single-Nucleotide Polymorphisms (SNPs)
Occur throughout the genome (occur about once in every 1000 nucleotides in people)
Typically 4000-5000 SNPs per individual
Main factor in making people different from each other
Variation in Genome Size
Overall size is measured in millions of base pairs (bp)
Not all DNA codes for proteins, therefore large genomes can contain a lot of non-functional DNA (junk dna)
Size does not mean complexity
Asexually reproducing species
All offsprings produced by asexual reproduction are clones of their parents
According to bio species concept, if a clone doesn’t interbreed with other clones, it’s a separate species
Ex. Blackberries
Horizontal gene therapy (HGT)
Genome sequencing has revealed separation between species is not always complete
Genes are sometimes transferred from one species to another even between distinctly related species
Frequent among bacteria
Does the bio species concept work with prokaryotes?
It is debatable, since there is so much gene transfer between bacteria
Shared trait of chromosome numbers
Members of the same species have the same # of chromosomes
Lack of diversity comes from reproducing sexually rather than asexually
DNA barcodes
Short section of DNA from one/ several genes which are distinctive enough to identify a species
