patterns of inheritance Flashcards
what is a genotype
the alleles of a gene carried by an organism
what is a phenotype
the expression of the gene (e.g.,. the characteristics, so blue eyes or brown eyes.
what is homozygous
A genotype, where one allele is present for a gene
what is dominant
expressed whether heterozygous (Aa) or homozygous (AA)
what is recessive
expressed only when in the homozygous state (aa)
what is a carrier
if an allele codes for a genetic disorder, a person with one recessive faulty allele is know as a carrier - they carry the trait but do not express the disorder
what is codominant
pairs of alleles which are both expressed when present
what is locus
the specific position of a gene on a chromosome.
what are the 3 sources of genetic variation
- mutations - gene and chromosomal
- meiosis (crossing over and independent assortment)
- sexual reproduction
what the 3 types of mutagenic agents
- physical agents
- chemical agents
- biological agents
what are physical agents
ionising radiation, e.g. x- rays
what are chemical agents
denominating agents
what are biological agents
alkylating agents, base analogy, viruses
what are the different types of chromosome mutations, that occur during meiosis
- deletion
- inversion
- translocation
- duplication
- non - disjunction
- polyploidy
- aneuploidy
what is a deletion mutation
removing a nucleotide from the gene
what is a inversion mutation
a reversal of position or order
what is a translocation mutation
when a chromosome breaks into to fragments and reattaches to different chromosomes
what is a duplication mutation
when one or more copies of a DNA segment is produced
what is a non - disjunction mutation
the failure of the chromosomes to separate
what is polyploidy mutation
an inheritable condition of processing more than two complete sets of chromosomes.
what is aneuploidy mutation
the presence of an abnormal number of chromosomes in a cell
what is an example of variation, that is only affected by the environment
scars, tattoos, accent
what is an example of variation, that is affected by the environment and genes
height and weight
what is discontinuous variation
genetic variation, prodcuing discrete phenotypes or two or more non - overlapping categories
what is continuous variation
variation producing phenotypic variation, where the quantitative traits vary by very small amounts, between one group and the next.
what does monogenic mean
determined by one gene
who was the first person to look at inheritance
Mendel
what did Mendel find?
discovered the presence of dominant and recessive alleles.
what is meant by F1
offspring of the first generation
what is meant by F2
offspring of second generation
what is a test cross
an organism, with an unknown genotype, but expressing the dominant phenotype is crossed with a homozygous recessive individual.
how are probabilities usually expressed
decimals, percentages, fractions.
what does dihybrid mean
- involves 2 gene loci.
- investigation, examine, simultaneous inheritance of the characteristics, are biohybrid crossed.
what did mendel find out
he deduced that the alleles of the two genes, are inherited independently of each other, so each gamete has one allele for each gene locus.
what are the steps for a dihybrid crosses
- write out parents phenotype.
- work out parents genotype.
- using foil, work out the different gamete genotypes.
- set up 4x4 punnet.
- combine the possible gamete genotypes.
- determine the phenotype ratio.
what is codominance
where both alleles, present in the genotype of a heterozygous individual, contribute, to the individuals blood type.
what is the MN blood group?
the MN blood group system, is controlled by a single gene with two alleles G^M and G^N. the gene codes for a particular protein on the surface of the erythrocytes
what is sickle cell anaemia ?
is caused, by a mutation in the gene, that codes for the Beta globin chain of haemoglobin.
what the definition of heterozygote
A genotype, where two different alleles are present for a gene.
key facts, about haemophilia
- unable to clot blood fast enough
- caused by a mutated form of the allele, for a blood clotting protein, called factor 8.
- this gene is found on teh non homologous region of the X chromosome (cannot be found on a Y chromosome).
describe the inheritance of haemophilia
if a female, is a carrier (one faulty an done functioning allele), then they are able to produce enough factor 8 to be symptomless
what is sex linkage
when a gene, is present of a sex chromosome.
what are the 4 observations that Darwin made?
- organisms produce more offspring than survive (overproduction of offspring.
- population numbers remain relatively stable, therefore there must be a struggle for survival.
- offspring are generally similar to their parents and features, are passed on through generations.
- variation exists (no two individuals are the same). some must be ‘better’ than others.
what is the theory of natural selection
- ‘survival of the fittest
- a process, where organisms, that ae better adapted to an environment, will survive and reproduce
- advantageous alleles, are passed onto offspring.
what is stabilising selection
- this normally occurs, when the organisms environment doesn’t change.
- it favours intermediate phenotypes (the ones in the middle of the range.
- stabilising selection, reduces the number of phenotypes
what is directional selection
- if there is a change in environment, individuals with the alleles for an extreme phenotype, are more likely to survive and reproduce.
- over generations, there is a gradual shift in the optimum value for the trait.
what is disruptive selection
- a type of natural selection, where the extreme values are selected for, over teh intermediates
- it is the rarest type of selection, out of the three.
what is the definition of population
individuals of the same species, living in the same place, at the same time that can freely interbreed.
what is population genetics
the study, of the changes in allele frequencies, within a population over time.
what is the hardy Weinberg principle
the frequencies of alleles, in a breeding population, wont change from one generation to another.
what are the assumptions, that need to be made of the Hardy Weinberg principle
- the population, is large enough to move sampling error negligible.
- mating within the population occurs at random.
- there is no selective advantage for any genotype, hence no selection.
- there is no mutation, migration, or genetic drift.
what is the biological concept of a species
- members of a species, are able to interbreed to produce fertile offspring, furthermore, they share same gene pool.
what are the two main types of isolating mechanisms
- geographical
- reproductive
what is speciation
the splitting of genetically similar population into two or more population that undergo genetic differentiation and eventually reproductive isolation, leadign to teh evaluation of two or more new species.
what is geographical isolation (allopatric speciation)
geographical isolation features, prevent gene flow, between isolated populations (e.g. rivers, mountains).
what is allopatric speciation
formation of two different species from one original species due to geographical isolation.
what is reproductive isolation
biological and behavioural changes, within a species may lead to reproductive isolation of one population to another.
what sympatric speciation
formation of two new species from one original species, due to reproductive isolation, while the populations inhabit the same geographical location.
what the link natural selection and speciation.
- organisms, that are more adapted to their environment, are more likely, to survive and pass on the alleles, that aided their success.
- this process, causes species, to change and diverge over time.
how else could genetic changes occur isolated populations which then leads to reproductive isolation.
genetic, changes, could affect the pheromones, of a species, thus making them unable to breed (attract males) thus making them reproductively.
what is artificial selection definition
- selective breeding of organisms, involves humans, choosing the desired phenotypes, and interbreeding, those phenotypes individually, therefore selectively (the genotypes, that contribute, to the gene pool of the next generation of the organisms.
what are the key steps in artificial selection (4 steps)
- farmer, chooses parents, with desirable characteristics, and allow them to mate.
- offspring, that have inherited alleles, with desirable characteristics are chosen.
- repeated over many generations
- allele frequency increases
what is the main impact of selective breeding
- as result of selective, the genetic diversity of the gene pool decreases.
give 4 factors, that reduce genetic diversity
- inbreeding depression
- susceptible
- less able to adapt/ less suspectable to a changing environment.
- loss of genetic resources old varieties.
