3.7 Genetics, populations, evolution and ecosystems

Allele

An alternative form of a gene.

Autosome

Any chromosome that is not a sex chromosome

Chromosomes

threadlike structures made of DNA molecules that contain the genes and is self replicating

Co-dominant alleles

Pairs of alleles that both affect the phenotype when present in a heterozygote

dominant allele

An allele whose trait always shows up in the organism when the allele is present.

gene pool

All the genes, including all the different alleles for each gene, that are present in a population at any one time

Genotype

genetic makeup of an organism

Haploid

An organism or cell having only one complete set of chromosomes.

Heterosomes

sex chromosomes

Heterozygous

possessing different alleles of genes at a locus on homologous chromosomes

heterogametic sex

The sex with two different sex chromosomes; a human male

homogametic sex

the sex with identical types of sex chromosomes; the human female

homologous chromosomes

Chromosomes that have the same sequence of genes and the same structure

Homozygous

An organism that has two identical alleles for a gene

locus

Location of a gene on a chromosome

Phenotype

features resulted from expression of genes and their interaction with the environment

reccessive allele

An allele that is masked when a dominant allele is present

sex linkage

the presence of a gene on a sex chromosome

test cross

the crossing of fertilisation between an unknown genotype showing the dominant phenotype and an individual showing the recessive phenotype

monohybrid cross

single breeding experiment involving one characteristic

dihybrid cross

inheritance of two characteristics which are controlled by different genes and have different alleles

Autosomal linkage

genes present on the same, non-sex chromosome. The closer they are located the less likely crossing over will split them

Epistasis

allele of one gene affects or masks the expression of another in the phenotype

ChiSquare

x^2\= sum off (observed - expected)^2 divided by the expected

Population

A group of individuals that belong to the same species and live in the same area

Hardy-Weinberg Principle

principle that allele frequencies in a population will remain constant from one generation to the next if it is:

a large population

mating is random

no migration

no mutations

no selection

Hardy-Weinberg equation

p = dominant

r = recessive

p + q = 1

p^2 + 2pq + q^2 = 1

variation

differences that exist between individuals, wide range of phenotypes determined by genotype/ environment

independent assortment

Independent segregation of genes during the formation of gametes - they can reshuffle in any combination. Occurs in anaphase 1 in meiosis

random fertilisation

any sperm can fertilise any egg

crossing over

Process in which homologous chromosomes exchange portions of their chromatids during meiosis, chiasmata. Occurs at prophase 1 in meiosis

evolution

frequency of an allele in a population over time

natural selection

A process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits.


1. variation
2. selection pressure
3. survival and reproduction
4. increase in alleles

Stabilising selection

Natural selection that favours intermediate variants by acting against extreme phenotypes

directional selection

occurs when natural selection favors one of the extreme variations of a trait

disruptive selection

form of natural selection in which a single curve splits into two; occurs when extremes are favoured, may give rise to new species.

Speciation

Formation of new species

genetic drift

Variations in allele frequencies in small populations due to chance. small populations so smaller gene pool, less genetic diversity so population can change relatively quickly leading to speciation.

allopatric speciation

The formation of new species in populations that are geographically isolated from one another.

sympatric speciation

The formation of new species in populations that live in the same geographic area, random mutations - behavioural isolation, ecological isolation, seasonal isolation, mechanical isolation, gametic isolation, gamete incompatibility, hybrid isolation.

genetic diversity

Differences in genotypes between members of a population which may occur due to mutations, meiosis, or random fertilisation.

structural adaptation

a physical feature of an organism's body having a specific function that contributes to the survival of the organism

Behavioural adaptation

what an organism does to survive in the unique conditions of its environment

physiological adaptation

a physical or chemical event that occurs within the body of an organism and enables survival

Ecology

Scientific study of interactions among organisms and between organisms and their environment

abiotic factors

Nonliving components of environment - temperature, water, light, nutrients

biotic factors

All the living organisms that inhabit an environment - competition, predation, disease

environment level of organisation

1. environment
2. biosphere
3. ecosystem
4. habitat or communities - population

Biome

major type of ecological community defined primarily by distinctive plant and animal groups

Biosphere

the part of Earth where life exists

Community

All the different populations that live together in an area

ecological niche

A specific role of a species within an ecosystem, including its use of resources, and relationships with other species.

carrying capacity

The largest population that an area can support

intraspecific competition

competition between members of the same species

interspecfic competition

competition between members of different species

competitive exclusion principle

Ecological rule that states that no two species can occupy the same exact niche in the same habitat at the same time

fundamental niche

The niche species could potentially occupy in absence of competition

realized niche

The niche species actually occupies when interspecific competition

quadrats sampling

random or systematic used to investigate the distribution of a population

transect sampling

a line randomly crosses a space and any organisms that are close to the line are counted.

Mark-release-recapture

A method of estimating the population size of motile organisms. It involves capturing a sample of the population, marking them and releasing them. At a later date, another sample is captured and the number of marked individuals recorded. The population size can be estimated using the following equation:

\
estimate size = number in 1st sample X number in 2nd sample / number marked in second sample

Succession

sequential change in community type over time, brought about by organism themselves.


1. pioneers arrive by chance and alter conditions to favour others
2. abiotic environment becomes less hostile
3. number and variety of habitats and niches increase
4. biodiversity increases
5. food webs become more complex
6. biomass increases
7. climax community reached

primary succession

An ecological succession that begins in an area where no biotic community previously existed

secondary succession

Succession following a disturbance that destroys a community without destroying the soil

conservation

protection and management of species and habitats in a suitable way.


1. management of succession - preserve ecosystems
2. seed banks - store of seeds from lots of different plants
3. captive breeding
4. fishing quotas - limit amount allowed to catch
5. protected areas