Chapter 20 Patterns Of Inheritance And Variation Flashcards
What is a genotype?
The combination of alleles an organism inherits for a characteristic
What is a phenotype?
The physical characteristics that make up the physical appearance of an organism which can be affected by the environment
What factors can affect variation?
Genetics
Environment
Describe what factors can affect Chlorosis in plants
Environmental factors
-Lack of light
-Mineral deficiencies (lacking Fe or Mg which are involved in chlorophyll production)
-Viral infections (interfere with the metabolism of cells)
Genetics
-Genes control the production of Chlorophyll
Describe the factors that can affect animal body mass
Environmental
-Quantity and quality of food eaten
-Amount of exercise
-Presence of disease
Genetics
-Mutations can result in alterations in fat deposition
What is an allele?
Different forms of the same gene
What are Phenotypical modifications?
Any changes that the environment makes to an individuals physical appearance are known as modifications.
What is a dominant allele?
Version of a gene that will always be expressed if present in an organism.
What is a recessive allele?
Version of the gene that is only expressed if two copies of this allele are present in an organism.
What is a Homozygous allele?
Two identical alleles for a characteristic
-Dominant or Recessive
What is a Heterozygous allele?
Two different alleles for a characteristic
What is Continuous variation?
A characteristic that can take any value within a range
Eg, skin colour, height
What is Discontinuous variation?
A characteristic that can only appear in specific (discrete) values
Eg, blood group, eye colour
What is the cause of continuous variation?
Genes and the environment
What is the cause of discontinuous variation?
Genetic
How is continuous variation controlled?
Controlled by a number of genes
How is discontinuous variation controlled?
Controlled by one or two genes
What is Monogenic inheritance?
A characteristic inherited on a single gene
Describe the steps required when interpreting genetic crosses
1- State the genotype of both parents
2- State the gametes of each parent
3- Use a punnet square to show the results of the random fusion of gametes during fertilisation
4-State the proportion of each genotype produced using a percentage or ratio
5- State the corresponding phenotype of each possible phenotypes
What is Codominance?
When different alleles of a gene are equally dominant and both are expressed in the phenotype.
How are codominance alleles represented?
A letter is chosen to represent the gene.
Eg, ‘C’ for colour of flowers
The different alleles are represented using a second letter which is shown as a superscript.
Eg, C^R = allele codes for red flowers
C^W = allele codes for white flowers
What are Multiple alleles?
A gene with more than two possible alleles
What is an autosomal gene?
A specific gene not on a sex chromosome
Give an example of a characteristic that can be coded for by multiple alleles?
Blood group can be determined by a gene with multiple alleles.
IA - Blood group A
IB - Blood group B
IO -Blood group O
IA and IB are codominant while IO is recessive.
Blood group A = IA IA or IAIO
Blood group B= IB IB or IBIO
Blood group AB= IAIB
Blood group O= IOIO
Which chromosome is known as the sex chromosome?
Chromosome 23
Pairs 1-22 are not sex chromosomes
What is a sex linked gene?
Genes carried by the sex chromosome
What is the cause of sex linked genes?
As the Y chromosome is smaller than the X chromosome there are some genes that males only have one copy of, this means that any recessive allele on a section of the X chromosome, missing in the Y chromosome, occurs more frequently in males.
What is dihybrid inheritance?
A characteristic inherited on two genes
Why can the actual ratio of offspring produced differ from the expected ratio of the genetic cross?
Fertilisation of gametes is random therefore it is due to chance which gametes fuse
Genes being studied are both on the same chromosome, if no crossing over occurs the alleles for two characteristics will always be inherited together.
What are linked genes?
Genes present on the same chromosome, they are inherited as a single unit.
What are recombinant genes?
New combination of alleles/ DNA from two sources
What are recombinant offspring?
Offspring that inherit different combinations of alleles compared to either parent
Describe how the number of recombinant offspring can be reduced
The closer the linked genes are on a chromosome the less likely they are to be separated during crossing over and fewer recombinant offspring produced.
What is recombination frequency?
The measure of the amount of crossing over that has happened in meiosis
What is the equation for recombinant frequency?
Recombinant frequency
=number of recombinant offspring
————————————————-
total number of offspring
Describe the results of recombinant frequency
Recombinant frequency of 50%= no linkage, genes are on separate chromosomes
Less than 50%/ <50%= indicates gene linkage and crossing over has been reduced
Are recombinant offspring advantageous?
Can be advantageous as the combination of different alleles compared to parents can facilitate adaption.
However, if the allele was already advantageous it can break apart the combination of alleles
What is the Chi squared statistical test used to measure?
Measures the difference between the observed results and the expected.
Helping to determines how likely results are due to chance.
Describe the different components of the
Chi squared equation
X^2= test statistic
Σ= sum
O= observed frequency
E= expected frequency
What does the degrees of freedom measure?
Number of comparisons being made
What is the equation for degrees of freedom?
n—1
N= number of categories
When are results considered significant using the chi squared statistical test?
If x^2 is less than the critical value then the results are not significant- null hypothesis is accepted
If x^2 is more or equal to the critical value then the results are significant - null hypothesis are rejected
What is the use of contingency tables?
Analyse and record the relationship between two or more categorical variables
When are contingency tables used to analyse genetics?
Record the expected cell frequency of a particular allele
What is the equation for expected cell frequency?
Expected cell frequency= (Row total x column total)
————————————
(Total frequency/ n)
What is epistasis?
The interaction of genes at different loci which leads to one gene preventing another gene from being expressed.
It is the result of these interactions that the phenotype of an organism is exhibited.
Continuous variation is a result of epistatis.
What is an epistatic gene?
A gene that affects the expression of another gene
What is a hypostatic gene?
A gene which is affected by another gene
What is dominant epistasis?
The inheritance of a dominant allele that prevents the expression of another gene
What is recessive epistatis?
Inheriting two recessive alleles that prevents another gene from being expressed
What is Allele frequency?
The relative frequency of an allele of a single gene in a population
What is a gene pool?
Sum of all gene in a population
How does evolution affect the frequency of alleles?
Evolution involves a long term change in the allele frequency of a population
How can allele frequency be calculated?
p + q= 1
Dominant allele= p
Recessive allele= q
What is the equation for the Hardy-Weinberg principle?
p^2 + 2pq + q^2 =1
Homozygous dominant= p^2
Homozygous recessive = q^2
Heterozygous = 2pq
What is the Hardy Weinberg equation used to calculate?
The proportion of alleles that are homozygous dominant, recessive or heterozygous.
Describe the factors that affect the frequency of alleles within a population affecting the rate of evolution
Mutations - formation of new alleles
Sexual selection - increased frequency of alleles
Gene flow- immigration/ emigration
Genetic drift- in small populations random mutations have significant impacts
Natural selection- leads to an increase in the number of individuals that have different phenotypes.
What factors affect population size?
Density dependent factors
Density independent factors
What are density dependent factors?
Dependent on the population size:
Eg, competition, predation, disease
What are density independent factors?
Affect populations of all sizes in the same way
Eg, climate change, natural disasters, seasonal change and human activities
What factors can cause large reductions in populations?
Bottleneck effect
Founder effect
Describe the bottleneck effect
Populations are significantly reduced and the frequency of alleles in the gene pool are decreased as a result of a catastrophic event.
Describe the founder effect
The population is reduced and frequency of alleles in the gene pool decreased as a result of the establishment of a community of a small population from a larger original population.
How can the distribution of different variants be displayed?
Normal distribution bell shaped curve
Describe what is meant by selection
Maintains a stable distribution in an environment
What are the different forms of selection?
Stabilising
Directional
Disruptive
What is stabilising selection?
The average is selected for positive selection and the extremes are selected against negative selection.
What is directional selection?
Occurs when there is a change in the environment and the most common phenotype is no longer the most advantageous. Organisms with extreme phenotypes are positively selected and allele frequency shifts to the extreme phenotypes and evolution occurs.
What is disruptive selection?
The extremes are selected for and the norm selected against
What is speciation?
The formation of a new species through the process of evolution
The organisms forming a new species are no longer able to interbreed and produce fertile offspring.
Describe the process of speciation.
Isolation of a population
-no gene flow or interbreeding
Mutations occur and different selection pressures select different characteristics
The change in phenotype from the accumulated mutations and allele frequency therefore change
-the difference is large enough to prevent fertile offspring
What are the different types of speciation?
Allopatric speciation
Sympatric speciation
What is allopatric speciation?
More common form of speciation caused by the original population being isolated as a result of geological separation.
The difference in the environment lead to selection pressures so the species adapt differently leading to different phenotypes.
What is sympatric speciation?
Less common form of speciation where members of a population that share a habitat become isolated, however they not physical barriers.
Eg, behavioural, temporal differences
Leads to reproductive isolation
What are reproductive barriers?
Barriers to successful interbreeding can form before or after fertilisation has occurred.
What are Pre-zygotic barriers?
Prevent fertilisation and the formation of a zygote
What are Post- zygotic barriers?
Species interbreed however the zygote is prevented from developing or the reproductive potential of offspring is reduced.
What are Post- zygotic barriers?
Species interbreed however the zygote is prevented from developing or the reproductive potential of offspring is reduced.
Give examples of pre- zygotic barriers
Geological, behavioural, temporal, mechanical, gametic or mechanical (reproductive organs are incompatible) isolation
Give examples of post zygotic barriers
Reduced hybrid viability- zygotes does develop or offspring are weak and prone to early death
Reduced hybrid fertility- healthy offspring infertile
Hybrid breakdown- offspring are fertile but produce weak second generation
What is artificial selection?
Selecting organisms to breed that display desirable characteristics
The offspring produced with the best desired characteristics are then interbred again
This reduces the overall allele frequency in a species gene pool
What is inbreeding?
The process of breeding closely related individuals
Describe the problems of inbreeding
-decreasing genetic diveristy of populations
-decreasing a populations adaptability to changing environments
-increased likelihood of offspring having homozygous recessive traits
-increased incidence of genetic disorders
-limited biological fitness
What are gene banks?
Stores of biological samples (frozen egg or sperm)
Seed banks
Describe the advantage of using gene banks?
Reintroduce genetic variety through outbreeding
What is outbreeding?
Crossing species with unrelated or distantly related members of the same species.
