6.1.2 Patterns of inheritance Flashcards
Define variation
the differences in characteristcs between organisms
Define interspecific variation
variation between different species
Define intraspecific variation
variation within a species
What are 2 causes of variation?
- the environment
- the genetic material (genotype)
What are 5 causes of genetic variation between individuals within a population?
- alleles - genes have different alleles
- mutations - changes to dna base sequence
- meiosis - independant assortment and crossing over
- sexual reproduction - each individual differs from the parents
- chance - individuals differ from siblings produced
- random fertilisation
- random mating
Define phenotype
the characteristics of an organism produced by alleles
Define genotype
the alleles an organism has
What is etiolation in plants? is it an environment or genetic controlled characteristic?
- environmental
- plants grow long and spindly due to lack of sunlight (environmental factor)
What is chlorosis in plants? is it an environment or genetic controlled characteristic?
- environmental
- plants turn yellow bc they dont produce enough chlorophyll
- due to no sunlight so plants stop wasting atp on chlorophyll production
- lack in minerals in soil e.g. Mg, Fe
What is body mass in animals ? is it an environment or genetic controlled characteristic?
continuous or discontinuous?
- genetic and environmental controlled
- mainly genetic
- continuous , has intermediates
Is height in animals influenced by genetic or environmental factors?
- genetic and environmental
- discontinuous if 2 disctinctive categories
- continuous if range
Define alleles
different versions of the same gene
Define dominant allele
an allele which is expressed even when there is only 1 copy
Define recessive allele
version of a gene that is only expressed when homoxygous/if dominant allele absent
Define homozygous
an organism that carries two identical alleles for a characteristic
Define heterozygous
an organism that carries two different alleles for a characteristic
Define carrier
a person carrying an allele which is not expressed in the phenotype but can be passed onto offspring
Define monogenic inheritance
characteristic controlled by one single gene
define dihybrid inheritance
characteristic controlled by two genes present on 2 different chromosomes at the same time
e.g. YYRR , yyrr
Define autosomal linkage
- two or more genes are located on the same (non-sex) chromosome
Define sex linkage
where genes are carried on the same sex chromosomes
- located on one of the sex chromosomes, its expression depends on sex of individual
Define codominance
- 2 different alleles of a gene are both dominant
- both alleles expressed in the phenotype
Define epistasis
- interaction of genes at different loci
the effect of one gene on the expression of another gene - (one gene either masks or supresses the other gene)
What are the 6 steps to draw a genetic cross diagram?
- state phenotypes
- state genotypes
- state gametes (circle them)
- use punnett square to show all results of random gamete fusion
- state proportion of each genotype
- state corresponding phenotype
What is meant by mutliple alleles?
A gene with more than 2 alleles
e.g. blood group
How is sex determnined in humans?
- sex genetically determined
- females XX
- males XY
What is the expected phenotypic ratio for monogenic crosses involving one homozygous dominant and one homozygous recessive
(e.g. RR x rr)?
3:1
dominant : recessive
What is the expected phenotypic ratio for dihybrid crosses involving one homozygous dominant and one homozygous recessive
(e.g. RRYY x rryy)?
9:3:3:1
dom both: dom 1st rec 2nd: rec 1st dom 2nd: rec both
What is the expected phenotypic ratio for codominant crosses involving one homozygous for 1 allele and one homozygous for other allele
(e.g. H big N H big N x H small s H small s)?
1:2:1
homoz for 1 allele: hetero : homoz for other allele
Why may expected ratios not occur if there is linkage between 2 genes?
- linkage means genes are located on same chromosome/autosome
- linked genes are inherited as one unit so no independant assortment
Why does crossing over disrupt autosomal linkage but only occasionally?
- autosomal linkage - when genes that are linked are found on other pairs of chormosomes
- more closer the genes are on chromosome/autosome the more linked they are
- less likely they are to be seperated during crossing over
Define recombinant offspring
different combinatons of alleles to either parent
Define recombinant frequency
the measure of the amount of crossing over that has happened in meiosis
How can epistasis occur?
- many genes interact epistatically
- multiple genes need to be expressed to produce enzymes
- if one of the genes is not expressed then one step is missing
- lack of enzyme normally produced when enzyme expressed means intermediate molecules necessary for the next reaction is not produced
- results in lack of substrate for next enzyme in the pathway
- so the expression of this gene not expressed in the phenotype
- gne is masked
Define hypostatic gene
- a gene affected by another gene
Define epistatic gene
a gene that affects the expression of another gene
Define dominant epistasis
and recessive epistasis
- dominant epistatis - if a dominant allele results in a gene having an effect on another gene
- recessive epistasis - two recessive alleles at a gene locus lead to lack of an enzyme
When would a chi-squared test be used to analyse data?
- to determine whether differences in the expected and observed results are significant or not (due to chance or real effect)
What are the meanings of each symbol in the equation for chi-test
x2 = test statistic
E = expected frequencies
O = obeserved frequences
What is the process of doing a chi-squared test and determining whether data from genetic cross supports the hypothesis?
1) calculate a chi-squared value using formula
2) work out degrees of freedom (NO diff phenotypes - 1)
3) compare chi-squared value with degrees of freedom number at 0.05
4) accept or reject null hypothesis
What does the null hypothesis always state?
there is no significant difference between the obsereved and expected results.
if x2 > or equal to critical value
(x2 larger than critcial value) …
there is a significant difference between the observed and expected results (something other than chance is causing the difference)
- the null hypothesis is rejected
if x2 < critical value…
(x2 smaller than critical value)
there is no significant difference between the observed and expected results
- the null hypothesis cant be rejected
How can number of genes coding for a characteristic influence variation?
- discontinuous variation - monogenic (characteristic determines by one gene)
- continuous variation - polygenic (characteristic determine by more than 1 gene)
Define continuous variation
- characteristic taking any value within a range
- no distinctive categories
- intermediates
- quantitative data
- polygenic genes
- influenced by enviromental and genetic
Define discontinuous variation
- characteristic that results in distinctive values
- e.g. blood type
- distinctive categories
- no intermediates
- qualitative data
- monogenic genes
- little/no environmental effect mostly genetic
Define polygenic
- phenotype is influenced by more than 1 gene
Define multifactorial
- when more than one factor causes a trait
Define evolution
- the change in inherited characteristics of a group of organisms over time
Define natural selection
- process by which organisms best suited to their environment survive and reproduce
- pass on their characeristics to their offspring through their genes
Define allele frequency
the relative frequency of a particular allele in a population
Define gene pool
the sum total of all of the genes in a population at any given time
Define selection pressure
- factors that affect an organisms chance of survival or reproductive success
Define selectively neutral allele
an allele which has no particular advantage or disadvantage
Define advantageous characteristic
and advantageous allele
advantageous characteristic - one form of a part of an organisms phenotype that provides it with a selective advantage
advantageous allele - a different version of a gene that provides a selective advantage to the organism
What is the process of adaptation/evolving characteristic evolving by natural selection?
1) due to natural selection
2) organisms within a species show variation in their characteristics causd by genetic variation
3) organisms whos characteristics are advantageous survive and reproduce
4) organisms pass allele encoding the advantageous characteristic onto offspring
5) repeated over many generations
6) over time frequency of this advantageous characteristic increases in the populations gene pool
Describe process of using selective breeding to improve specific characteristic e.g. crop resistance to diesease/ udder size
1) use artifical selection
2) breed 2 individuals with desired characterstic (e,g. disease resistance)
3) test desired characterstic by e.g. germinating seeds and exposing to disease
4) select offspring with best characteristic (e.g resistance) and breed best offspring together
5) continue procss over many generations
6) to perserve genetic divesity breed plants from. differenet areas
what is artificial selection?
when humans choose particular organisms to breed together in order to produce a desired characterstic in offspring
What are 5 factors that can affect the evolution of a species?
- mutation
- sexual selection
- gene flow
- genetic drift
- natural selection
define genetic drift
- change in populations allele frequencies that occurs due to chance /mutations rather than selective pressures
What are the consequences of genetic drift on the genetic diversity of a population?
- appearance of new allele has greater impact on smaller population
- genetic drift results in loss of rare alleles and can decrease size of gene pool
Define genetic bottleneck and what are the consequences of it on the genetic diversity of a population
genetic bottleneck - an event such as a natural disaster that causes big reduction in populations size. leads to reduction of variety of alleles in gene pool and cause large changes in allele frequencies
- lead to reduced genetic biodiversity within the population
What is meant by the founder effect
and what are the consequecnes of it on the genetic diversity of a population?
- when a small number of individuals become isolated and form a new population with small number of different alleles and a limited gene pool.
- without gene flow (new alleles introducted) rare alleles become a lot more common in the population = reduced genetic variation
What are 2 examples of the founder effect in humans?
- Amish people in america descended from 200 germans
- rarely marry outside their religion so genetic pool v small
- have unusally high genetic frequency for certain genetic disorders - Afrikaner population in south africa descendant from few dutch settlers
- have unsually high alle frequecny of allele causing huntingdons disease
Define stabilising selection
and what are the consequecnes of it for a population
occurs when environmental conditions remain the same
- norm or average is selcted for
- new characteristcs selected against
-1. consequecnes - reduction in frequency of allele at new characteristics and increase in average alleles
= low biodivesity
Define directional selection
- occurs when change in environmental conditions
- normal phenotyepe no longer advantageous
- individuals with phenotypes suited to new conditions survive and pass on their genes
- allele frequency shifts towards extreme phenotypes and evolution occurs
Define disruptive selection
and consequences of it on the population
- new characteristics/extremes selected for and norm selcted against
- allele frequency shifts towards extreme phenotypes
Which assumptions are made in the hardy-weinberg principle
- no mutations
- no selective pressure
- random mating
- no migration
- large population
What does the hardy-weinberg principle allow us to estimate?
- allows to estimate frequecny of alleles in a population
- and if allele frequency is changing over time
How to use hard-weingberg equation for calculating allele frequency
- must add up to 1.0
- p + q = 1.0
- p = frequecny of dominant allele
- q = frequecny of recessive allele
How to use hard-weingberg equation for calculating genotype frequency
- must add up to 1.0
- p2 + 2pq + q2 = 1.0
- p2 = freq of homozygous dominant
- 2pq = freq heterozygous
- q2 = freq of hommozygous recessive
Define species
the smallest and most specific taxonomic group
- organisms of the same species can reproduce to give fertile offspring
Define speciation
when does speciation occur?
- the formation of a new species
- when populations of same species become reproductively isolated
Define allopatric speciation
speciation that results from a physical barrier
e.g. river, mountain, volcanoe eruptions, earthquakes
- conditons on either side of barrier different so different selection pressures so diff characteristics favoured and natural selection happens
- allele frequencies for advantageous characteristics increase
- eventually individuals from different population change so much that they can no longer breed to produce fertile offspring
Define sympatric speciation
speciation that results from a non-physical barrier
e.g. a mutation that stops two organisms from producing fertile offspring
What are the stages of speciation? ( formation of a new species)
- members of population become isolated and no longer interbreed with rest of the population
- alleles within the groups continue to undergo random mutations
- accumulation of mutations and changes in allele frequencies over many generations eventually lead to large changes in phenotype
- different populations can no longer interbreed to form fertile offspring
- two species have been formed
how geographical isolation lead to evolution of new species
- two populations are geogrpahically seperated so cant interbreed so no gene flow between the groups
- random mutation occurs in one group which proves advantageous so individuals with advantageous characteristic reproduce more and pass on advantageous characteristic on
- accumulation of mutations and changes in allele frequecnies over many generations evetnrually leads to large changes in phenotype
- so 2 populations can no longer interbreed to form fertile offspring so new species formed
Define pre-zygotic reproductive barrier and post-zygotic reproductive barrier
- pre-zygotic reproducitve barrier - prevent fertilisation and formation of zygote
- post-zygotic reproductive barrier- reduce viability or reproductive potential of offspring
what are 5 types of prezygotic reproductive barrier types and 2 types of post-zygotic reproductive barrier.
- pre-zygotic:
1. seasonal changes - different flowering/mating seasons
2. geographical
3. behavioural - individuals develop courtship rituals that are not attractive to main population
4. anatomical
5. genetic - post-zygotic
1. not viable, offspring infertile
Define artificial selection
humans select individuals with desirable characteristics to breed together
What is the process of artificial selection?
- individuals with desirable traits picked and bred together to produce offspring
- offspring with best desirable traits bred
- process done over many generations until majority of population has desirable characteristic
What are the benefits and limitations of artificial selection?
benefits:
- offspring will have desirable characteristics
- faster than natural selection
limitations:
- interbreeding can occur
- lack of genetic variation
- more susceptible to disease
- ethics
- can create genetic bottlenecks
What are examples of artificial selection in crop plants and animals?
plants:
wheat
- seeds used from plants producing larger fruit/veg
- high yield
animals:
- dairy cows
- high milk yield
What are ethical considerations surrounding use of artificial selection in dogs?
- unnatural
- religious objections bc harming animals
- animal welfare issues
- lack of genetic diversity so animals more susceptible to illness
- breeders care about appearance not health
- interbreeding risk
Define inbreeding and problems it can cause
inbreeding - breeding of closely related individuals
- genetically similar so likely to have same recessive alleles so result in offspring being homozygous for recessive traits and affected by genetic disorders
- reduce ability of organisms to survive and reproduce
Define outbreeding and its importance for inbred (or small) populations
outbreeding - breeding of distantly related organisms
- introduce new alleles and genes into gene pooland increase genetic diversity
- offspring less likely to have homozygous recessive alleles and genetic disorders
Define seed bank and gene bank
- seed bank - keep sample of seeds from both wild typ and domesticated variaties
- gene bank - store biological samples
What is the importance of seed banks/gene banks for artificial selection in plants and animals?
- alleles from gene banks jused to increase genetic diversity
- allow traits that were bred out to be reintroduce
- to revert back to point before negative traits were introduced
Define gene
A short section of DNA that codes for a particular protein
