IB Biology: Diversity of Species

Directional Selection

A mode of natural selection where one extreme of a trait is favored, leading to a shift in the population's trait distribution.

Disruptive Selection

A type of natural selection that favors extreme values over intermediate values, potentially leading to speciation.

Stabilizing Selection

A form of natural selection that favors intermediate variants of a trait, reducing variation.

Fitness

The ability of an individual to survive and reproduce in its environment; for example, a meerkat's alarm-calling behavior increases the survival rate of its group.

Natural Selection

The process through which individuals with favorable traits are more likely to survive and reproduce, passing those traits to future generations.

Artificial Selection

The intentional breeding of plants or animals for specific traits by humans.

Reproductive Isolation

Barriers that prevent species from mating and producing fertile offspring, leading to speciation over time.

Homozygous

An organism that has two identical alleles for a specific gene, such as AA or aa.

Heterozygous

An organism that has two different alleles for a specific gene, such as Aa.

Phenotype

The observable physical or biochemical characteristics of an organism, determined by its genotype.

Genome

The complete set of genes or genetic material present in a cell or organism.

Genomes GG, Gg, gg

GG is homozygous dominant, Gg is heterozygous, and gg is homozygous recessive.

Variation

Differences among individuals of the same species, essential for adaptability in changing environments.

Species Concepts

Two main species concepts: Biological species concept, which defines species based on reproductive isolation, and Morphological species concept, which defines species based on physical characteristics.

Geographical Isolation Effects

Short-term: Reduced gene flow between populations. Long-term: Potential speciation as genetic divergence occurs.

Chromosomal Difference in Humans and Chimpanzees

Humans have a different number of chromosomes (46) and different chromosomal arrangements compared to chimpanzees (48).

Chromosome Count in Humans

Humans have 46 chromosomes in somatic cells and 23 chromosomes in gamete cells.

Chromosome Pairs in Humans

Humans have 23 pairs of chromosomes, one from each parent, due to sexual reproduction.

Chromosome Description

Chromosomes are described by their number, size, shape, and the genes they carry.

Chromosome Number and Genome Length

The number of chromosomes does not directly indicate the length or content of the genome.

Hybrids and Infertility

Hybrids of two species are usually infertile due to mismatched chromosome numbers, preventing proper meiosis.

Karyotype Interpretation

A person's karyotype can be named and interpreted by analyzing the number and structure of their chromosomes.

Alleles of a Gene

Different forms of a gene that occupy the same position on homologous chromosomes.

Single Nucleotide Polymorphism (SNP)

A variation at a single position in a DNA sequence among individuals.

Homozygous for a Trait

An individual with two identical alleles for a trait.

Heterozygous for a Trait

An individual with two different alleles for a trait.

Genome Measurement Unit

The unit used to measure genomes is often base pairs.

Goal of Genome Sequencing

The main goal is to determine the complete DNA sequence of an organism's genome.

Variation Size Comparison

Variation is typically larger within a species than between species.

Genome Size Measurement

Genome size is measured in base pairs.

Transposons

DNA sequences that can change their position within the genome and may affect gene expression.

Large Genomes and Functioning Genes

Large genomes may not contain more functioning genes due to non-coding DNA and repetitive sequences.

Geographically Separated Populations

Geographically separated populations may develop distinct base sequences due to mutations and selection pressures.

Bottleneck Effect

After a bottleneck event, the gene pool of a population will show reduced genetic diversity due to random loss of alleles.

Biological Species Concept Limitations

The biological species concept does not work well for organisms that reproduce asexually or for fossil species.

Biological Species Concept and Prokaryotes

The biological species concept is not applicable to prokaryotes, as they reproduce asexually.

Chromosome Number Consistency

Members of the same species usually have the same number of chromosomes.

Gametes and Somatic Cells Types

Gametes are haploid and somatic cells are diploid.

Dichotomous Key Purpose

A dichotomous key is used for identifying organisms through a series of choices.

Environmental DNA Barcoding

Species can be identified from environmental DNA using barcodes, which helps determine biodiversity.