A3.1 Diversity of Organisms

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