Patterns Of Inheritance-6.2 Flashcards
What is genotype?
-the genetic constitution of an organism(the alleles it has for a gene)
What is phenotype?
-the visible characteristics of an organism
-due to interactions of the genotype and the environment
What contributes to phenotypic variation?
-both environmental and genetic factors
What are gene mutations a factor for?
-a genetic factor for phenotypic variation
-mutations can be harmful,advantageous or neutral
What are two things that mutations that occur during gamete formation are?
-persistent-they can be transmitted through many generations without change
-random-they are not directed by a need on the part of the organism which they occur
What are chromosome mutations?
-a genetic factor for phenotypic variation
-chromosome mutations may occur during meiosis
What are mutagens?
-certain physical and chemical agents that can increase the rate of mutation
-e.g.
physical agents- X-ray, UV light
Chemical agents-mustard gas, nitrous acid
Biological agents -some viruses, food contaminants such as mycotoxins from fungi
What is deletion in relation to chromosome mutations?
-part of the chromosome, containing genes and regulatory sequences is lost
What is inversion in relation to chromosome mutations?
-a section of the chromosome may break off, turn through 180 degrees and then join again
-although the genes are all still present some may now be too far away from their regulatory nucleotide sequences to be properly expressed
What is translocation in relation to chromosome mutations ?
-a piece of chromosome breaks off and then becomes attached to another chromosome
-this may also interfere with the regulation of the genes on the translocated chromosome
What is duplication in relation to chromosome mutations ?
-a piece of a chromosome may be duplicated
-over expression of genes can be harmful ,because too many of certain proteins or gene-regulating nucleic acids may disrupt metabolism
What is non-disjunction in relation to chromosome mutations ?
-one pair of chromosomes or chromatids fails to separate, leaving one gamete with an extra chromosome
-when fertilised by a normal haploid gamete ,the resulting zygote has one extra chromosme
-down syndrome or trisomy 21 is caused by non-disjunction
What is aneuploidy in relation to chromosome mutations ?
-the chromosomes number is not an exact multiple of the haploid number for that organism
-sometimes chromosomes fail to separate during meiosis e.g trisomy
What is polyploidy in relation to chromosome mutations?
-if a diploid gamete is fertilised by a haploid gamete
-the resulting zygote will be triploid (it has three sets of chromosomes )
-the fusion of 2 diploid gametes can make a tetraploid zygote
-many cultivated plants are polyploid- they have more than 2 sets of chromosomes
Genetic variation resulting from sexual reproduction has contributed to …
-evolution
What may lead to genetic variation during meiosis ?
-allele shuffling (swapping of alleles between non-sister chromatids ) during crossing over in prophase 1
-independent assortment of chromosomes during metaphase/anaphase 1
-independent assortment of chromatids during metaphase/anaphase 2
What does random fusion of gametes at fertilisation lead to?
-creates more genetic diversity
-any male gamete can potentially combine with any female gamete from an organism of the same species
-the random fertilisation of gametes that are already genetically unique produces extensive genetic diversity among the resulting offspring
What are 2 characteristics of gametes produced by meiosis?
-individual and genetically dissimilar
-haploid -containing only one of each pair of homologous chromosomes and one allele for every gene
What are some examples of environmental factors that causes variation?
-having a scar following an injury
-diet of an animal influencing weight
-etiolation-a condition in plants characterised by weak stems and small pale leaves due to insufficient exposure to light
What is an allele?
-a version of a gene
What does heterozygous mean?
-a pair of homologous chromosomes carrying two different alleles for a single gene
-not true-breeding/non pure breeding
What does homozygous mean?
-a pair of homologous chromosomes carrying the same alleles for a single gene
-true-breeding/pure breeding
What does monogenic mean?
-determined by a single gene
-can be visualised using a punnett square
What is a monohybrid cross?
-genetic inheritance cross of a characteristic determined by one gene
E.g. punnett square
What must you show in a genetic cross?
1-parental phenotype
2-parental genotype
3-possible gametes
4-offspring genotype
5-offspring phenotype
6-proportion of each phenotype (phenotypic ratio)
What does F1 generation stand for?
-first filial generation
What do you always circle when doing genetic crosses?
-gametes
What is F2 generation?
-second generation
What is the test cross?
-a method used to work out the unknown genotypes of individual organisms that is expressing a dominant phenotype
How is a test cross done?
The individual in question is crossed with an individual that is expressing the recessive phenotype
The resulting phenotypes of the offspring provide sufficient information to suggest the genotype of the unknown individual
If there are any offspring expressing the recessive phenotype then the unknown individual must have a heterozygous genotype
What is dihybrid?
-genetic inheritance cross for a characteristic determined by 2 genes
-it involves 2 gene loci
What is discontinuous variation?
-genetic variation producing discrete phenotypes
-two or more non-overlapping categories
-each phenotype class is clearly discernible from another in a qualitative way
-they are no or very few intermediates between the different phenotypes (e.g. you are either male or female and you only have one of the possible 4 blood groups)
How many genes influence discontinuos variation?
-usually determined by the alleles of a single gene locus, they are monogenic
-sometimes the alleles of two genes interact to govern a single characteristic
-in either case:
->different alleles at a single gene locus have large effects on the phenotype
->different gene loci have quite different effects on the characteristic
Genes at different ____ may interact to influence one characteristic and produce __________ _________ , as in ________
-loci
-discontinuous variation
-epistasis
What is continuous variation ?
-variation that produces phenotypic variation where the quantitative traits vary between very small amounts between one group and the next
Where the genetic ________ between individuals, even if they are related , within a population shows a range with a smooth gradation (series of successive changes) between the many intermediates, it is described as __________ ________
-variation
-continuous variation
What are examples of continuous variation?
-height
-hair colour
-foot size
-eye colour
How many genes influence continuous variation?
-many genes are involved in determining characteristics such as height, hair colour
-so such characteristics are described as polygenic
Why do phenotypic categories vary in a quantitative way in continuous variation?
-as alleles of each gene may contribute a small amount to the phenotype
-therefore the alleles have an additive effect on the phenotype, as a result the phenotypic categories vary in a quantitative way
-as well as this the greater the number of gene loci contributing to the determination of the characteristic, the more continuous the variation (the greater the range)
-the study of such inherited characteristics is called quantitative genetics
Does the environment have a greater influence on monogenic or polygenic characteristics ?
-the environment has a greater effect on polygenic characteristics than it does on monogenic characteristics
What is natural selection ?
-mutations and migration introduce new alleles into populations
-some individuals within a population will be better adapted than others to the environment , due to differences in their genotypes and phenotypes
-these individuals are more likely to survive and reproduce passing on advantageous alleles
-over time allele frequencies within the population will change -this is natural selection
-natural selection may maintain constancy of a species as well as leading to new species
When does stabilising selection normally occur?
-normally occurs when the organisms’ environment remains unchanged
What is stabilising selection?
-natural selection leading to constancy within a population
-intermediate phenotypes are FAVOURED and extreme phenotypes are selected against
-alleles for extreme phenotypes may be removed from the population
-stabilising selection reduces genetic variation within a population
What is directional selection ?
-a type of natural selection that occurs when an environmental change favours a new phenotype and so results in a change in the population mean
-directional selection is used by plant and animal breeders to produce a desirable trait
What is genetic drift?
-if a population descends from a small number of parents, the gene pool will lack genetic variation
-some alleles resulting from mutation confer neither an advantage nor disadvantage on the individual so there will be no selecting pressure acting upon them
-a catastrophic chance event (e.g flood,shortage of food,disease outbreak) which leads to the death of many in the already small population may lead to one of the alleles disappearing from this population
-when the population recovers and increases in size, it will have less genetic diversity than before and may lack particular alleles. These alleles did not disappear due to selection pressure but due to genetic drift
What can genetic drift arise after?
What can genetic drift arise as a result of ?
-genetic drift can arise after a genetic bottleneck or as the result of the flounder effect
What is a genetic bottleneck ?
-a sharp reduction in size of a population due to environmental catastrophes such as earthquakes , floods, disease or human activities such as habitat destruction or over hunting reduces the genetic diversity
-as the population expands it is less genetically diverse than before
What is the founder effect?
-when a small sample of an original population establishes in a new area its gene pool is not as diverse as that of the parent population
What is speciation?
-the splitting of a genetically similar population into two or more populations that undergo genetic differentiation and eventually reproductive isolation
-leading to the evolution of two or more new species
What is allopatric speciation?
-the formation of 2 different species, due to geographical isolation (geographical mechanism)
-as the isolated populations will be subject to different selection pressures in 2 different environments, they then undergo independent changes to the allele frequencies and/ or chromosome arrangements within their gene pools
-these genetic changes may be the result of mutation, selection and genetic drift
-as a result of natural selection each population becomes adapted to its environment
What is sympatric speciation?
-reproductive mechanism
-formation of 2 different species from one original species, due to reproductive isolation, while the populations inhabit the same geographical location
Why may sympatric speciation occur?
-biological and behavioural changes within a species may lead to reproductive isolation of one population from another
-genetic changes can also lead to reproductive isolation e.g. change in chromosome number may- prevent gamete fusion, make zygotes less viable so they will fail to develop
-mating between members of the reproductively isolated populations may also be prevented by mutations leading to changes in - courtship behaviour, animal genitalia or plant flower structure
What is artificial selection ?
-selective breeding of organisms
-involves humans choosing the desired phenotypes and interbreeding those phenotypes individually, therefore selecting the genotypes that contribute to the gene pool of the next generation of these organisms
What is the agent of selection in natural selection ?
-the environment is the agent of selection during natural selection
What is the agent of selection during artificial selection?
-humans are the agents of selection
Briefly describe artificial selection
-breeders select individuals with the desired traits and allow them to interbreed
-at the same time they prevent those without the desired characteristics from breeding
What are desirable characteristics in plants that may be selectively bred for?
-increase yield
-pest and disease resistance
-weather resistance
What are some desirable characteristics in animals that may be selectively bred for?
-docility
-ability to be trained
-high egg or milk production
-high mass of meat
-hunting ,retrieving , companionship-dogs
How may breeders selectively breed plants?
-breeders may grow plants of a particular type under conditions they wish these plants to withstand e.g. low /high temperatures or high salinity
-they will then select the individuals that grow the best under these conditions and cross pollinate them
-collect and sow the seeds and repeat this process over generations
What do gene banks store ?
-they store genomes but in their organisms
-they maintain a resource of genetic material for use in selective breeding
-this includes for wild types
What are 4 examples of gene banks?
-wild populations of organisms
-seed banks
-sperm banks
-botanic gardens and zoos
What are some ethical considerations of artificial breeding?
-domesticated animals retain many juvenile characteristics making them friendly, docile and playful but less able to defend themselves. This can make them easy prey
-livestock animals selected to have more lean meat might succumb to low environmental temperatures during winter if they were not housed
What are some ethical considerations for extreme examples of artificial selection e.g. dogs?
-the traits in dogs considered desirable by humans might put dogs at a selective disadvantage if they had to survive in the wild
-some breeds through interbreeding have susceptibility to disease e.g.boxer-cancer and heart disease and Dalmatian- congenital deafness ,heart disease
-some coat colours selected for aesthetic reasons would fail to camouflage the animal
What are some factors that affect allele frequencies within populations and hence the genetic diversity within a gene pool?
-population size
-mutation rate
-migration
-non-random mating
-natural selection
-changes to environment
-genetic drift
-gene flow
What 4 things does the Hardy-Weinberg principle assume?
-the population is large enough to make 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 are the 2 equations for the Hardy-Weinberg principle?
-p^2 + 2pq + q^2 = 1
-p+q=1
-p=the frequency of the dominant allele
-q=the frequency of the recessive allele
-p^2=the frequency of the homozygous dominant genotype
-2pq=the frequency of the heterozygous genotype
-q^2= the frequency of the homozygous recessive genotype
What does the null hypothesis state?
-that there is no statistically significant difference between the observed and expected data
-any difference is due to chance
What are the steps to using the chi-squared test to determine if the significance of the difference between observed and expected results?
1-calculate value for chi-squared (normally best to use a table for this)
2-determine the number of degrees of freedom(=number of categories- 1)
3-determine the value of p from a distribution table using the probability value of 0.05 (we need to know the probability of our results being the result of chance is greater than 5%
4-decide whether the difference is significant at the p=0.05 level of probability
What does it mean if our chi-square value is smaller than critical value ?
-the difference between our observed and expected is due to chance and is not significant
-null hypothesis can be accepted
How do you determine the number of degrees of freedom?
Number of degrees of freedom= number of categories- 1
What is the equation used when two individual events occur simultaneously?
Product of individual probabilities= combined probability of occurrence
What is codominant?
-where both alleles are expressed in the heterozygote resulting in a different phenotype
What is multiple alleles?
-more than two alleles for a single gene
What is sex-linkage?
-a gene whose locus is on the X (or Y ) chromosome
What is autosomal linkage?
-gene loci present on the same autosome (non-sex chromosome)that are often inherited together
What is epistasis?
-when one gene modifies or masks the expression of a different gene at a different locus
Explain how selective breeding can lead to an increased yield of wheat plants
—crossbreed high yielding plants
-measure yield
-crossbreed high yielding offspring
-continue this over generations
-prevent self pollination
