Patterns of inheritance and variation Flashcards
What do plants with pale or yellow leaves have?
Chlorosis
Why do plants have chlorosis?
Cells don’t produce normal amounts of chlorophyll
What is a result of chlorosis?
Reduces ability to make food by photosynthesis.
What factors affect whether a pant has chlorosis?
Environmental
What environmental factors cause chlorosis?
- Lack of light
- Mineral deficiencies
- Virus infections
How does both genetic and environmental factors affect leaves?
Genetic factors code for green leaves and environment results in final leaf appearance.
What is an organisms body mass determined by?
Genetic and environmental factors.
Define genotype.
Genetic make up of an organism.
Define phenotype.
Observable characteristics of an organism.
What are the actual characteristics that an organism displays influenced by?
The environment
For most genes in your body … alleles are inherited.
Two
What are modifications?
Changes made to a phenotype by the environment which are not inherited.
What is a dominant allele?
Version of the gene that will always be expressed if present in the organism.
What is a recessive allele?
Only be expressed if 2 copies of this allele are present in an organism.
Define homozygous.
Two identical alleles for a characteristic.
Define heterozygous.
Two different alleles for a characteristic.
Define continuous variation.
Characteristic can take any value within a range.
What causes continuous variation?
Genetic and environmental.
What genes control continuous variation?
Polygenes
What are polygenes?
A number of genes.
Give an example of continuous variation.
Mass
Define discontinuous variation.
Characteristic can only appear in specific values.
What causes discontinuous variation?
Genetic (mostly)
What genes control discontinuous variation?
One or two genes
Give an example of discontinuous variation.
Blood group, round and wrinkled pea shape
What is speciation?
Formation of a new species as a result of evolution.
Define species.
Members of species will be able to interbreed to give fertile offspring.
What can lead to speciation?
Alleles can undergo random mutations.
Members of a population can become isolated.
Accumulation of mutations and changes in allele frequencies over many generations eventually lead to large changes in phenotype.
What is allopatric speciation?
Members are separated from each other by a physical barrier.
Explain allopatric speciation.
Environments differ in the different areas, so different selection pressures. So different physical features are benefical and so are passed on to their offspring.
How can allopatric speciation lead to the founder effect?
If a small population is separated.
What is sympatric speciation?
Occurs when members of two different species interbreed and form fertile offspring. New offspring will have different number of chromosomes. This stops gene flow.
Give an example of sympatric speciation.
Fungus farming ants
Give an example of allopatric speciation.
Galapagos islands
What are the results of prezygotic fertilisation barriers?
Prevent fertilisation and the formation of a zygote.
What are postzygotic reproductive barriers?
Reduce viability or reproductive potential of offspring.
Define polymorphic.
Display more than one distinct phenotype.
Define wild type allele.
Allele coding for the most common characteristic.
What is artificial selection/ selective breeding?
The selection for breeding of plants or animals with desirable characteristics by farmers or breeders.
What is inbreeding?
Breeding of closely related individuals.
What are the problems of inbreeding?
Limits the gene pool and so decreasing genetic diversity reduces the chances of a population of inbred organisms evolving and adapting to changes in their environment.
What are seed banks?
Keep seeds of wild type and domestic varieties. An important genetic resource.
What are gene banks?
Store biological samples. Usually frozen.
What do gene banks store?
Sperm, eggs
What are alleles from gene banks used for?
Increase genetic diversity in a process called outbreeding.
What is outbreeding?
Breeding unrelated or distantly related varieties.
What are the results of outbreeding?
Reduces occurrence pf homozygous recessives and increases the potential to adapt to environmental change.
What does the Hardy-Weinberg principle state?
In a stable population with no disturbing factors, the allele frequencies will remain constant from one generation to the next and there will be no evolution.
What are the two equations used in the Hardy-Weinburg principle?
p^2 + q^2 = 1
p + q = 1
What is p^2?
Frequency of homozygous dominant genotype in the population.
What is q^2?
Frequency of homozygous recessive genotype in the population.
What is 2pq?
Frequency of heterozygous genotype in the population.
What is the allele frequency?
Frequency of a particular allele in a population.
What is the gene pool?
Total sum of all the genes in a population at any given time.
What does the Hardy-Weinberg principle assume?
Population of diploid organisms is large, isolated, no mutations, no selection pressures.
What will upsetting the equilibrium of an environment result in?
Evolution
What factors lead to changes in allele frequencies and so affect the rate of evolution?
- Mutations lead to new alleles which give genetic variation.
- Gene flow changes the allele frequency within a population.
- Genetic drift. Change in allele frequency due to random mutations.
- Natural selection leads to an increase in individuals with characteristics which improve their chances of survival.
- Sexual selection leads to an increase in frequency of alleles which code for characteristics which improve mating success.
What is gene flow?
Movement of alleles between populations.
What sort of populations does genetic drift occur in?
Small
Give two types of limiting factors which affects the size of a population.
1) Density-dependent factors
2) Density-independent factors
What are density-dependent factors?
Dependent on population size.
What do density-dependent factors include?
Competition, predation, communicable disease.
What are density-independent factors?
Affect populations of all sizes.
What do density-independent factors include?
Climate change, natural disasters, human activities.
What is monogenic inheritance?
Inheritance of a single gene
What is codominance?
Two different alleles occur for a gene, which are both equally dominant. Both alleles expressed in phenotype.
Why for codominance are an upper case and lower case letter not used, what is used instead?
Upper and lower implies one is dominant over the other, instead a letter is chosen and then a superscript.
What are multiple alleles?
When genes have more than two alleles.
For multiple alleles, why can only two alleles be present in an individual?
Organisms only carry two versions of a gene.
What is the 23rd pair of chromosomes known as?
Sex chromosomes
What is larger, the X or the Y chromosome?
X- contains many genes not involved in sexual development.
What are sex linked genes?
Genes carried on the sex chromosomes.
What does it mean that the X is larger than the Y chromosome?
There are a number of genes on the X chromosome that males only have one copy of.
What is the result of males only having one copy of some genes?
Any characteristic caused by a recessive allele on the section of the X chromosome, which is missing in the Y chromosome, is more frequent in males.
Give an example of a sex-linked disorder.
Haemophilia
What happens in people with haemophilia?
Blood clots slowly.
Who are more at risk of getting haemophilia?
Males
Why are males more likely to get haemophilia?
If a male inherits the recessive allele on their X chromosome, they cannot have a corresponding dominant allele on their Y chromosome, and so develop the condition.
What does a dihybrid cross show?
Inheritance of two different characteristics, caused by two genes, which may be located on different pairs of homologous chromosomes.
Why can the actual ratio of offspring produced differ from the expected?
- Fertilisation of gametes is a random process.
- Genes are linked so, if no crossing over occurs the alleles will be inherited together.
What are linked chromosomes?
Linked
What are recombinant offspring?
Different combinations of alleles than either parent.
How are genes less likely to separated during crossing over?
If they are close to each other om the chromosome.
How are lined genes inherited?
As one unit.
What is autosomal linkage?
When genes that are linked are found on one of the other pairs of chromosomes.
Why are the ratios observed in dihybrid crosses significantly different from those expected?
Due to linkage
What does a recombinant frequency of 50% indicate?
There is no linkage and genes are on separate chromosomes.
What does a recombinant frequency of less than 50% indicate?
Genes are linked.
As the degree of crossing over reduces, the recombinant frequency gets…
…smaller.
What does the degree of crossing over determined by?
How close the genes are on the chromosome.
What is the null hypothesis?
There is no significant difference between what we expect and what we observe.
What does it mean if the chi squared value is less than the critical value?
No significant difference
What does it mean if the chi squared value is greater than the critical value?
Significant difference.
If the chi squared value is less than the critical value do we accept or reject the null hypothesis?
Accept
If the chi squared value is more than the critical value do we accept or reject the null hypothesis?
Reject
What is epistasis?
Interaction of genes at different loci.
What is a hypostatic gene?
A gene affected by another gene.
What is a epistatic gene?
A gene that affects the expression of another gene.
What are population bottlenecks?
Large reductions in population size.
What is a positive of genetic bottleneck?
Beneficial mutation will have a much greater impact and lead to quicker development of a new species.
What is the founder effect?
Smaller populations arise due to the establishment of new colonies by few isolated individuals.
What is the founder effect an extreme example of?
Genetic drift.
How does the founder effect work?
New populations have a much smaller gene pool and display less genetic variation.
What is stabilising selection?
Norm is selected for and extremes are selected against.
What is a result of stabilising selection?
Reduction in frequency of alleles at the extremes and increase in frequency of average alleles.
What is directional selection?
Occurs when there is a change in the environment and the normal phenotype is no longer the most advantageous.
Where does the allele frequency shift towards in directional selection?
Towards extreme phenotypes.
What is an example of stabilising selection?
Birth weight of babies
What is an example of direction selection?
Peppered moths during the industrial revolution.
What is an example of disruptive selection?
Finches observed by Darwin in the Galapagos
What is disruptive selection?
Extremes are selected for and norm is selected against.
