Mod 6 Flashcards
(59 cards)
Understanding DNA Mutations
Mutations are changes in nucleotide sequences of DNA.
Insertion/deletion mutations lead to frameshift changes.
Point mutations involve the replacement of one base pair with another.
Nonsense mutations cause premature stop codons, resulting in truncated proteins.
Missense mutations alter amino acid production, while silent mutations do not affect the amino acid sequence.
Understanding the Impact of Genetic Mutations
Mutations can have neutral effects with no impact on the organism.
Neutral mutations may occur in non-coding DNA or as silent mutations.
Beneficial mutations, like trichromatic vision in humans, enhance capabilities.
Harmful mutations, such as those in the CFTR protein, can lead to diseases like cystic fibrosis.
The effects of mutations depend on the organism’s environment.
Understanding the Lac Operon: A Model of Transcriptional Control
The lac operon regulates the expression of beta-galactosidase in E. coli.
It comprises structural genes and control sites for transcription regulation.
The promoter region is where RNA polymerase binds to start transcription.
The operator region is the binding site for the inhibitor protein.
The inhibitor is produced by a regulator gene located outside the operon.
Regulation of Gene Transcription by Glucose and Lactose
High glucose and low lactose inhibit transcription.
Repressor binds to the operator region under high glucose conditions.
Low glucose and high lactose allow lactose to bind the repressor.
Binding causes a shape change in the repressor, rendering it ineffective.
RNA polymerase can then bind to the promoter, enabling transcription.
Controlling Gene Expression through Transcription Factors
Transcription factors regulate gene expression by turning genes on or off.
They interact with promoter sequences in DNA to control transcription.
Gene expression can also be regulated at the post-transcriptional level.
Editing of primary mRNA transcripts removes introns, forming mature transcripts.
The resulting mature transcripts consist only of exons, which code for proteins.
Post-Translational Control of Gene Expression
Gene expression can be regulated after translation.
Adrenaline is an example of a protein that can be activated post-translationally.
Cyclic AMP plays a crucial role in activating proteins like adrenaline.
The process starts when adrenaline binds to its receptor.
Adenylate cyclase converts ATP to cyclic AMP, initiating a cascade of reactions.
Role of Homeobox Genes in Development
Homeobox genes regulate the body plan development of organisms.
They code for transcription factors that control gene expression.
These genes switch on and off specific genes during developmental stages.
Homeobox genes are crucial during processes like limb formation in humans.
They are organized in clusters known as hox clusters.
Understanding Apoptosis: The Programmed Cell Death
Apoptosis is programmed cell death crucial for body development.
It plays a vital role in tissue development in both plants and animals.
This process involves an ordered series of biochemical events.
Apoptosis helps maintain a constant number of cells to prevent cancer.
During apoptosis, cell contents are broken down and disposed of by phagocytes.
Opposite of necrosis, cell death resulting from damage and release of hydrolytic enzymes
What occurs during apoptosis?
During the process, enzymes break down the cytoskeleton of the cell, DNA and proteins. As the contents of the cell are broken down, the cell begins to shrink and break up. Subsequently, the cell fragments are engulfed by phagocytes and destroyed.
Understanding Phenotypic Variation
Two types of phenotypic variation exist: discontinuous and continuous.
Discontinuous variation includes categories like shoe size and blood type.
Continuous variation involves quantitative differences, such as height and weight.
Environmental factors like diet can influence phenotypic variation.
Genetic factors also play a significant role in phenotypic differences.
Understanding Meiosis and Genetic Variation
Meiosis produces haploid gametes with half the number of chromosomes.
It is a form of cell division that promotes genetic variation.
Genetic variation occurs through crossing over of chromatids.
Independent assortment of chromosomes creates diverse combinations.
Meiosis leads to genetically different cells essential for reproduction.
Key Meiosis / Genetic Variation Definitions
Allele – alternative form of a gene
Locus – the specific position of a gene on a chromosome, the two alleles of a gene are found at the same loci on the chromosome pairs
Phenotype – observable characteristics of an organism which are as a result of genotype and environment
Genotype – the alleles present within cells of an organism, for a particular trait or characteristic
Dominant – only a single allele is required for the characteristic to be expressed, that allele is always expressed in the phenotype
Recessive – the characteristic is only expressed if there is no dominant allele present
Homozygous – two identical alleles
Heterozygous – two different alleles
Codominance – both alleles contribute to the phenotype
Linkage is the phenomenon where genes for different characteristics are located at different loci on the same chromosome and so are inherited together.
Monogenic inheritance – when a phenotype or trait is controlled by a single gene. For instance, cystic fibrosis where the individuals with doubly recessive genotype are affected.
Dihybrid cross – inheritance of two genes
Sex linkage – expression of an allele dependent on the gender of the individual as the gene is located on a sex chromosome
Autosomal linkage – genes which are located on the same chromosome (which is not a sex chromosome) and tend to be expressed together in the offspring
What is Epistasis?
Epistasis – the interaction of different loci on the gene, one gene locus affects the other gene locus. One gene loci can either mask or suppress the expression of another gene locus.
Recessive epistasis occurs when the presence of a recessive allele prevents the expression of another allele at a second locus. Recessive epistasis gives the ratio of 9:3:4. Dominant epistasis is when a dominant allele at one locus completely masks the alleles at a second locus. Dominant epistasis gives a ratio of 12:3:1.
Understanding the Chi Squared Test
The chi squared test assesses differences between observed and expected results.
It requires a sample size of over 20 and is applicable to discontinuous variation data.
This test evaluates the null hypothesis, which asserts no difference exists between observed and expected results.
Results are compared to a critical value to determine the significance of differences.
If the chi squared value exceeds the critical value, the null hypothesis is rejected, indicating a significant difference.
What is the Hardy-Weinberg Equation?
The Hardy-Weinberg Equation can be used to estimate the frequency of alleles in a population and to see whether a change in allele frequency is occurring in a population over time.
Hardy-Weinberg Formulae
p = the frequency of the dominant allele (represented by A)
q = the frequency of the recessive allele (represented by a)
For a population in genetic equilibrium:
p + q = 1.0 (The sum of the frequencies of both alleles is 100%.)
(p + q)2 = 1 so p2+ 2pq + q2 = 1
The three terms of this binomial expansion indicate the frequencies of the three genotypes:
p2 = frequency of AA (homozygous dominant)
2pq = frequency of Aa (heterozygous)
q2 = frequency of aa (homozygous recessive)
Understanding Ecological Niches and Adaptations
A species’ niche defines its role in the environment.
Competition occurs among species sharing the same niche.
Natural selection favors better adapted species.
Adaptations can be anatomical, behavioral, or physiological.
Examples include urine concentration in desert mammals and mating calls.
Understanding Natural Selection and Evolution
Natural selection favors individuals better adapted to their environment.
Fitter individuals pass advantageous alleles to future generations.
Evolution is driven by changes in allele frequency in a gene pool.
Natural selection leads to the survival of the fittest.
Over time, these processes contribute to species adaptation and diversity.
Understanding Evolution through Natural Selection
Populations exhibit a variety of phenotypes.
Environmental changes alter selection pressures.
Individuals with advantageous alleles have better survival rates.
Advantageous alleles are inherited by offspring.
Over generations, allele frequencies shift, driving evolution.
Key Factors Influencing Species Evolution
Genetic drift leads to changes in allele frequency due to uneven reproduction.
The genetic bottleneck results from rapid population size reduction affecting future genetic variation.
Natural disasters can cause genetic bottlenecks by drastically decreasing population size.
The founder effect reduces genetic diversity from a small number of ancestors.
Isolated populations are particularly vulnerable to genetic drift and reduced diversity.
Understanding Speciation: The Birth of New Species
Speciation occurs when populations become separated and unable to interbreed.
Allopatric speciation is driven by physical barriers that isolate populations.
Reproductive isolation reduces gene flow and leads to different selection pressures.
Natural selection causes allele frequencies to change over time, resulting in new species.
Sympatric speciation can occur within the same geographic area due to genetic errors.
Understanding Artificial Selection in Agriculture
Artificial selection is driven by human intervention to breed desired traits.
Dairy cows are selectively bred based on their milk yield for optimal production.
Hormones are used to enhance egg production in high-yielding cows.
Bread wheat is a hexaploid hybrid with 42 chromosomes, requiring larger cells.
Domesticated wheat combines genomes from wild species for improved characteristics.
Overview of DNA Sequencing Process
DNA sequencing starts with mapping the genome to locate specific genes.
DNA is fragmented using restriction enzymes and inserted into bacterial artificial chromosomes.
This process creates a genomic DNA library.
Fragments from bacterial cultures are further broken down using restriction enzymes.
Sequencing employs Sanger’s chain-termination technique with DNA polymerase.
Understanding DNA Sequencing Process
DNA samples are split into four sequencing reactions.
Each reaction includes standard nucleotides, DNA polymerase, primers, and fluorescently labelled modified nucleotides.
Incorporation of modified nucleotides stops replication, creating fragments of varying lengths.
High resolution electrophoresis separates DNA fragments based on size, detecting single base differences.
Fragments are visualised under UV light to read the base sequence from the gel.
