genetics and evolution

autosomal chromosome / gene

Any chromosome / gene that is not a sex chromosome

Haploid (n)

An organism / cell or cell having only one complete set of chromosomes e.g. eggs and sperm

gamete

sex cell

diploid (2n)

(genetics) an organism or cell having two sets of chromosomes or twice the haploid number

homozygous dominant

Genotype with two dominant alleles.

homozygous recessive

Genotype with two recessive alleles.

Heterozygous

An organism that has two different alleles for a trait

monohybrid cross

An experimental mating of individuals looking at only one gene.

cystic fibrosis

a genetic condition caused by a mutated recessive (autosomal) allele which results in thick mucous in the lungs and digestive tract of the individual

Huntington's disease

a disease caused by a dominant (autosomal) gene that results in degradation of brain function

phenylketonuria (PKU)

a genetic disorder caused by a mutated recessive (autosomal) allele where the individual cannot break down phenylalanine (an amino acid) which results in a build-up in the body and brain development problems and seizures

complete dominance

a relationship in which one allele is completely dominant over another

Codominance

when both alleles are equally dominant and are both in the expressed phenotype e.g. red flower x white flower --> flower with red and white petals

sickle cell anemia

a genetic disorder that causes abnormal hemoglobin, resulting in some red blood cells assuming an abnormal sickle shape; follows a co-dominant inheritance pattern

incomplete dominance

Situation in which one allele is not completely dominant over another allele and the offspring is a blend of the two phenotypes e.g. red flower x white flower --> pink flower

multiple alleles

three or more forms of a gene that code for a single trait e.g. blood type

Sex determination in humans

Based on the presence of a Y chromosome which can only come from the male/dad

sex-linked traits

Traits controlled by genes located on sex chromosomes.

colour blindness and hemophilia

these are examples of sex-linked traits

autosomal dominant (pedigree chart)

If both parents are affected and an offspring is unaffected, the trait must be dominant (parents are both heterozygous); All affected individuals must have at least one affected parent; If both parents are unaffected, all offspring must be unaffected (homozygous recessive)

autosomal recessive (pedigree chart)

If both parents are unaffected and an offspring is affected, the trait must be recessive (parents are heterozygous carriers); If both parents show a trait, all offspring must also exhibit the trait (homozygous recessive)

x-linked dominant (pedigree chart)

If a male shows a trait, so too must all daughters as well as his mother; An unaffected mother cannot have affected sons (or an affected father); X-linked dominant traits tend to be more common in females (this is not sufficient evidence though)

x-linked recessive (pedigree chart)

If a female shows a trait, so too must all sons as well as her father as she would only pass on a recessive allele and males only inherit one X chromosome from their mother; An unaffected mother can have affected sons if she is a carrier (heterozygous) since she can pass down either dominant or recessive allele; X-linked recessive traits tend to be more common in males (this is not sufficient evidence though)

discrete data

data that can be counted, is often in categories, and cannot be measured; represented in a bar graph

continuous data

data that is measured using a tool, the values exist on a spectrum and can be subdivided infinitely; represented on a scatter plot

polygenic inheritance

when a single characteristic is controlled by multiple alleles e.g. skin colour

natural selection

organisms that are more adapted to their environment are more likely to survive, reproduce, and pass on their beneficial alleles/traits to their offspring

evolution

the change in allele frequency/heritable characteristics in a population over time

allele frequency

the percentage/frequency of a specific allele in a population

abiotic factor

non-living factors (the environment) e.g. water, pH, salinity, sunlight, temperature, etc.

biotic factors

a living factor in an environment e.g. other organisms

adaptation

an inherited characteristic that makes an individual suited to its environment and way of life

heritable

can be passed on to offspring

fitness

an organism's ability to pass its genetic material to its offspring. Species that are more "fit" can pass on their genes and ensure their survival.

mutation

permanent change in DNA sequence

Causes of variation

random mutations and sexual reproduction (i.e. meiosis --> new combinations of alleles)

carrying capacity

Largest number of individuals of a population that a environment can support

factors that affect natural selection

overproduction of offspring and competition for resources

selection pressure

a variable in the environment which causes a certain phenotype of an organism to have a better chance of surviving and reproducing (can be negative or positive)

sexual selection

A form of natural selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates.

Abiotic selection pressures

changes in temperature, light, humidity, pH, salinity

homologous structures

Structures in different species that are similar because of common ancestry e.g. pentadactyl limb

adaptive radiation

When organisms appear to have quickly evolved in a range of different directions from a common ancestor (an example of divergent evolution)

analogous structures

structures that have similar functions but have completely different structures (resulting from convergent evolution)

divergent evolution

when two or more species sharing a common ancestor become more different over time

convergent evolution

Process by which unrelated organisms independently evolve similarities when adapting to similar environments (due to similar selective pressures)

selective breeding (artificial selection)

The process of humans breeding organisms that results in offspring with desired genetic traits.

molecular phylogeny

analysis of the genetic material of organisms to establish their evolutionary relationships

gene flow

is the movement of genetic information (i.e. alleles) from one population of a species to another

mutation

change in a DNA sequence that affects genetic information

mutagen

A chemical or physical agent that interacts with DNA and causes a mutation.

SNP

when a single nucleotide is changed in a sufficiently large proportion of the population (typically >1%)

substitution mutation

Mutation in which a single base is replaced, potentially altering the gene product.

insertion mutation

a mutation in which one or more nucleotides are added to a gene --> results in a frameshift

deletion mutation

a mutation in which one or more nucleotides are removed from a gene --> results in a frameshift

degeneracy of the genetic code

More than one codon codes for an amino acid, making third codon position a wobble one

anucleate

without a nucleus

sister chromatids

Identical copies of a chromosome; full sets of these are created during the S-phase of interphase.

centromere region

a constricted area where the two members of each chromatid pair are held together

kinetochore

A specialized region on the centromere that links each sister chromatid to the mitotic spindle.

Centrosome

A structure in animal cells containing centrioles from which the spindle fibers develop.

Centrioles

the structures that enable the formation of spindle fibres

diploid

containing two complete sets of chromosomes, one from each parent (2n)

Haploid

An organism or cell having only one complete set of chromosomes (n)

functions of mitosis

growth, replacement/repair, asexual reproduction

product of mitosis

two identical daughter cells that are diploid

product of meiosis

four genetically unique haploid cells

interphase

where the cell grows, carries out its cellular activities, and where DNA replication takes place

prophase in mitosis

Chromosomes supercoil/condence, nuclear membrane breaks down, spindle fibres/microtubules form

metaphase in mitosis

microtubules grow and attach to kinetochore, chromosomes line up at cell equator

anaphase in mitosis

sister chromatids are pulled apart towards opposite poles

telophase in mitosis

reversal of events that occurred in prophase

cytokinesis in plants

cell plate forms a cell wall between the two daughter cells

cytokinesis in animals

cleavage furrow constricts like a drawstring to separate the cells

meiosis I results in

homologous chromosomes being separated, generating haploid daughter cells

meiosis II results in

sister chromatids being separated to create four genetically unique daughter cells

crossing over

the exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in offspring.

independent assortment

the way that one homologous pair lines up during Metaphase 1 does not affect how the others line up

non-disjunction in meiosis I

Error in meiosis in which homologous chromosomes or sister chromatids fail to separate resulting in some gametes having too many chromosomes and some having none.

Variation in traits

differences within and between species

binomial classification system

genus then species (capitalised), italicised; multiple species can have the same genus, but the species name is specific to each species.

morphological species concept

characterizes a species by body shape and other structural features

biological species concept

defines a species as a group of populations whose members have the potential to produce fertile offspring.

sexual dimorphism

Differences in physical characteristics between males and females of the same species.

infertile

unable to reproduce

Speciation

The process of a pre-existing species splitting into two or more new species

Speciation - physical barrier

parts don't fit

Speciation - geographical barrier

in different areas

Speciation - behavioural barrier

different courting behaviours or wake/sleep patterns

Speciation - temporal barrier

different mating times

The process that leads to speciation

a gradual process where there is a lack of gene flow due to a type of barrier; each new population acquires different mutations at different rates, and is also subjected to different selective pressures; over time the differences accumulate until the two populations cannot interbreed if they were to come back together.

All diploid cells have…

an even number of chromosomes

karyotyping

involves isolating condensed chromosomes and staining them to highlight their banding patterns

Karyogram

the image produced by karyotyping to show homologous pairs of chromosomes

aneuploidy

When there is one or more extra or missing chromosome in the cell/organism. e.g. Trisomy 21 is a type of aneuploidy

chromosome 2 hypothesis

that chromosome 12 and 13 in chimps fused to form chromosome 2 in humans

Genome

all of the genetic material in an organism; varies in size across species and is determined by the amount of DNA