Answer:
Explanation:
An error in cell division occurred in the known species, leading to the development of an autopolyploid tetraploid offspring that evolved into the new species.
Bread production involves the production of carbon dioxide bubbles to make the bread dough rise. These carbon dioxide bubbles occur as a result of yeast cells undergoing ___.
A. alcoholic fermentation
B. cellular respiration
C. anaerobic respiration
D. lactic acid fermentation
Answer:
The correct answer will be- Alcoholic fermentation.
Explanation:
Alcoholic fermentation is one of the complex set of anaerobic reactions which takes place in certain micro-organisms.
The process of alcoholic fermentation converts the glucose into ethanol which is performed in two steps.
Glycolysis converts the glucose to the form two molecules of pyruvic acid and two molecules of ATP. The pyruvic acid is then converted to ethanol and two molecules of carbon dioxide. The formation of carbon dioxide allows the dough to rise and thus the selected option is the correct answer.
Relate restriction enzymes to recombinant DNA
Answer:
Read the explanation section.
Explanation:
Restriction enzymes basically used in genetic engineering. Particularly in recombinant DNA technology. Restriction enzymes have two properties, which are very much useful in recombinant DNA technology.
First, they cut DNA into fragments or small pieces. This cutting is done to make the size of the DNA into a suitable one for cloning purposes.
Second, many restriction enzymes make staggered cuts that create single-stranded glutinous ends. These ends are favorable to the formation of recombinant DNA.
Restriction enzymes are used to cut DNA at specific recognition sites, allowing fragments of DNA to be spliced into another DNA molecule to create recombinant DNA. DNA ligase is used to join the cut DNA fragments together and create the final recombinant DNA molecule.
Explanation:Restriction enzymes, also known as restriction endonucleases, play a crucial role in the field of recombinant DNA technology. They are naturally occurring bacterial enzymes that cut DNA at specific recognition sites, which are usually palindromic sequences. These enzymes create fragments of DNA that can be spliced into another DNA molecule to form recombinant DNA. DNA ligase, on the other hand, is an enzyme that joins the cut DNA fragments together to create the recombinant DNA molecule.
In a species of ground finch that inhabits the Galápagos Islands, the average beak size increased over several generations from 9 mm to 10 mm after a drought that left only large hard seeds for the finches' food source. This is an example of_________.a. stabilizing selectionb. genetic driftc. disruptive selectiond. directional selection
Answer:
d. directional selection
Explanation:
Directional selection is a form of natural selection that occurs when a particular extreme phenotype of a species is highly favored and thrives more than the other extreme phenotype. This is particularly influenced by environmental changes resulting in differences in the survival between both extreme phenotypes.
In the Galapagos Islands during drought, the seeds to be fed on by finches are mostly large in size, giving rise to the survival of only finches with large beak size of 9 mm to 10 mm as against finches with small beak size. Finches with large beak sizes are favored over finches with phenotypic traits of small beak sizes.
In sexual selection, individuals with certain inherited characteristics are more likely to obtain mates than other individuals. This often results in ____ _____, differences between the sexes in size, appearance and behavior
Answer:
Sexual dimorphism.
Explanation:
Sexual selection may be defined as the mode of natural selection in which the species choose its mate and prevent the other's individual mating. This provide better reproductive success in nature.
The sexual selection depends upon the attractive colors, size and behavior of other partner. The sexual selection results in sexual dimorphism as the male and female of the species can be easily distinguished. Their mating organ, behavior are different in opposite sexes.
Thus, the correct answer is sexual dimorphism.
Dispersion patterns tend to be highly dependent on the spatial scale of the observer. For example, football players lined up on the scrimmage line are clumped at the scale of 100 yards but uniformly dispersed at the scale of a meter. An example of animals that are likely to be clumped at a large scale but uniformly distributed at a small scale is:____________
Answer:
Explanation: red squirrels, who actively defend territories
Ant nests in an abandoned field
Buffalo grazing on a prairie
Bluegills swimming in a northern lake
Calico cats are nearly all females because the alleles for the different colors that appear are carried on the X chromosomes. Males are rarely multicolored, because they can only carry one form of the allele. What is this an example of?
Answer:
This is example of Inactivation of X chromosome.
Explanation:
In calico cats, Fur color is carried on Chromosome X. Female cats have two X chromosomes. When they have two X chromosomes, some of these X chromosomes in some cells throughout the body are INACTIVATED and they are seen as black dots under microscope. These black dots are called Barr Bodies. Normally calico cats have brown and white fur color, and also black color due to this barr bodies. X in activation or the formation of barr bodies are not observed in males because they have only one X chromosome.
What organisms usually cause urinary tract infections (UTIs) in older men in conjunction with prostatic hypertrophy?
Answer: Escherichia coli bacteria cause urinary tract infection in older men
Explanation:
A urinary tracts infection is an infection around the urinary systems like bladder, kidneys and urethra. It is majorly caused by Escherichia coli bacteria in older men. It can be treated by medical professional when diagonised. This infection is common in men of 50 years upward.
Prostrate hypertrophy is an infection of the prostrate gland that cause enlargement of prostrate gland making urine difficult. The disease is age associated, it is found in older men of 50years upward. It is caused by bacteria.
Two species of frogs belonging to the same genus occasionally mate, but the offspring fail to develop and hatch. What is the mechanism for keeping the two frog species separate?
A) the postzygotic barrier called hybrid inviability
B) the postzygotic barrier called hybrid breakdown
C) the prezygotic barrier called hybrid sterility
D) gametic isolation
Answer:D
Gametic isolation is a type of prezygotic barrier where the gametes (egg and sperm) come into contact, but no fertilization takes place. Gametes may be unable to recognize one another in different species.
Furosemide is a loop diuretic drug that inhibits the pump responsible for active reabsorption of Na and Cl in the nephron loop. Which of the following is one of the common side effects of furosemide?
a. hypernatermia due to increased Na resorbtion
b. hypertension
c. excessive water resorption in the kidneys
d. uncreased natriuresis (Na loss)
Answer:
The correct answer is d unceased natriuresis.
Explanation:
Furosemide is used as drug for the treatment of diuresis. Furosemide helps to inhibit the protein pump that helps in the active reabsorption of sodium and chloride ions in the loop of henle of nephron.
This ultimately result in the loss of excess sodium ions from the body which leads to natriuresis.
If natural selection over the time period of Eukaryote evolution has favored a DNA architecture in Eukaryotes that keeps genes turned off except when needed, this structure would be _____.
Answer:
If natural selection over the time period of Eukaryote evolution has favored a DNA architecture in Eukaryotes that keeps genes turned off except when needed, this structure would be nucleosomes.
Explanation:
The nucleosome is the fundamental unit of "packaging" of eukaryotic DNA. This structure contains chromatin, which is a fundamental substance of the cell nucleus and consists of the combination of DNA with proteins. In eukaryotic cells the structure of chromatin is the organization in which DNA is presented in the cell nucleus, and is responsible for masking (protecting) certain sequences, while allowing free access to identical ones. Local chromatin has effects on gene expression, forming special structures that actively bring amplifiers closer to promoters. The active or open chromatin may contain regulatory sequences, promoters, transcribed sequences and regions bound to insulating chromatin proteins. Heterochromatin is a chromatin that is usually located in the vicinity of the nuclear envelope, here genes that are not normally expressed are located, although there are portions of DNA in the constitutive heterochromatin that are transcribed.
The life-threatening food allergy reaction of anaphylactic shock is most often caused by: a. almonds, yeast breads and oranges. b. tomatoes, yeast breads and bananas. c. peanuts, milk and shellfish. d. soy, fish and strawberries.
Anaphylactic shock, a severe and life-threatening allergic reaction, is most often caused by peanuts, milk, and shellfish.
Explanation:Anaphylactic shock is a life-threatening allergic reaction that can occur when a person with a food allergy is exposed to the allergen. The most common food allergens that can trigger anaphylaxis are peanuts, milk, and shellfish. These foods contain proteins that can elicit an immune response in individuals with allergies, leading to symptoms such as difficulty breathing, rapid pulse, and decreased blood pressure.
Learn more about anaphylactic shock here:https://brainly.com/question/32657070
#SPJ3
Anaphylactic shock is most often caused by peanuts, milk, and shellfish, triggering a rapid immune response and severe symptoms. Epinephrine is used to counteract the effects of anaphylaxis.
Explanation:Anaphylactic shock, a life-threatening food allergy reaction, is most often caused by peanuts, milk, and shellfish.
When an individual with a severe allergy consumes or comes into contact with these allergens, it triggers a rapid immune response. This immune response leads to the release of histamine and other chemicals, causing symptoms such as swelling, difficulty breathing, and a drop in blood pressure.
Epinephrine is used to counteract the effects of anaphylaxis and can be life-saving. It is important for individuals with known severe allergies to carry automatic epinephrine injectors at all times.
Learn more about Anaphylactic shock here:https://brainly.com/question/38999011
#SPJ6
Explain how twin studies were used to note the differences in the brain between people who have this diagnoses and the co-twins who do not. (What looks different about the brains of the twins where only one had the disease?
Answer:
The studies of monozygotic or identical twins are used to analyze the degree of genetic influence versus the environmental contribution on a specific pathology, this is because monozygotic twins share 100% of their genes, meanwhile the dizygotic twins share only the 50% of their genes, approximately.
The studies conducted on twins are a special type of epidemiological study because this relation allows the researchers to evaluate and compare the influence of genetic and environmental variables.
Explanation:
Researchers have conducted twin’s studies to discuss the “nature and nurture” question, it is well known that genetics are associated with the environmental factors to produce the human individualities.
However, the twin studies are a perfect model to evaluate the shared genetic and environmental factors for the trait of interest; in addition, it can help to estimate the proportion of variance in a particular genetic variation versus the amount of influence of shared or unshared environment. It also can reduce the amount of genetic and/or environmental variability in a genetic study.
Sahu, M., & Prasuna, J. G. (2016). Twin studies: A unique epidemiological tool. Indian journal of community medicine: official publication of Indian Association of Preventive & Social Medicine, 41(3), 177.
Investigators interested in studying the activation of apoptosis inject cytochrome c into the cytosol of two types of mammalian cells: cells that are normal and cells in which Bak and Bax have been inactivated by mutation.
How would these cells be predicted to respond?
Answer: Both cell types will undergo apoptosis
Explanation:
cytochrome C functions in the mitochondria and plays an important role in the synthesis of Adenosine Triphosphate (ATP). When a cell receives an apoptosis stimulus Cytochrome C is released from the mitochondria into the cystol to activate caspase cascade thereby committing the cell to the death process. Cytochrome C triggers programmed cell death through apoptosis. Cytochrome C release is caused by swelling of the mitochondrial matrix.
The reclamation of a sanitary landfill occurs _______. A. after the cells have been compacted B. before the clay liner is installed C. after the landfill is capped D. before the landfill is capped E. after the clay liner is installed
Answer: option D
Reclamation of sanitary landfills occurs before the land fills is capped.
Explanation:
Reclamation of sanitary landfills is a method use to expand the municipal solid wastes sanitary landfill capacity so as to avoid high cost of purchasing another land.
Sanitary landfills is an area of land where wastes is allow to decompose or degraded chemically, physically and biologically until it is safe.
This reclamation is done before the landfills is capped so as to avoid high cost of getting another land.
In order to determine if individuals from separate populations are indeed distinct species, Drosophila biologists often test to see if individuals from different populations will mate with each other. This is an application of the ________ species concept.
Answer:
Biological species contest.
Explanation:
Different species concept are introduced to describe the exact definition and classification of species. Some species concept are biological species contest, morphological species concept and ecological species contest.
According to biological species contest, the group of individual that can breed among themselves and not with the other group. Here, the Drosophila species has been classified by the biologist depending on their mating ability to their group of individual only.
Thus, the answer is biological species contest.
The 150-million-year-old Archaeopteryx fossil has birdlike features such as feathered wings, but it also has characteristics that we associate with living reptiles. Which of the following are considered reptilian characteristics of Archaeopteryx?a. teeth in the jawsb. claws on the ends of each digit in the "hands"c. long, bony tail
Answer:
-teeth in the jaws
-claws on the ends of each digit in the "hands"
-long, bony tail
Explanation:
Most of the reptiles have teeth on the jaw bone or broad teeth that make up their jaw.
A claw can be described as a curved appendage which can either be found at the end of fingers. This feature is common in reptiles.
The animals present in the reptiles group have known to possess tails. Usually, the tails are long in size
Hence, all these characteristics can be considered as reptilian characteristics.
How would being able to detect damaged members of a prey species be beneficial to individual prey?
Predators often target damaged or weaker individuals in a prey species, leading to higher survival rates for the fittest members. Batesian mimicry—where harmless species mimic the warning colors of harmful ones—is an example of how species evade predation.
Explanation:Being able to detect damaged members of a prey species would be beneficial to individual prey as it would decrease loss through predation. Predators often target weaker or injured individuals as they are easier to catch. This could lead to an increase in survival rates of those who are healthy and fit.
For instance, some predators learn to avoid consuming particular prey due to their coloration. Other species have adapted to mimic this coloration to evade being consumed, even though they might not taste unpleasant or carry harmful toxins. This phenomenon is known as Batesian mimicry, where a benign species imitates the warning coloration of a dangerous one. As long as they share the same predators, this strategy serves to safeguard the harmless species. Many insect species mimic the coloration of wasps or bees, which are stinging, venomous insects, thereby discouraging predation.
Learn more about Predation and Batesian Mimicry here:https://brainly.com/question/34875971
#SPJ11
This group of enzymes digests the majority of ingested fat.
a. pancreatic lipases.
b. pepsin and stomach acid.
c. bile salts.
d. lingual lipases.
Answer:
Option A
Explanation:
Undigested fats include all those fatty acid and lipids which do not have the ability to dissolve in water. This inability makes them difficult elements for digestion. All this undigested fat accumulates and reaches the intestine for digestion as globs. Globs are emulsified by the bile salts and are broken down into smaller fat droplets. The smaller fat droplets have large surface area and hence now they can be acted upon by the fat-digesting enzyme pancreatic lipase. Thus, the first set of enzymes that act upon the undigested fats in the intestine are pancreatic lipase
Hence, option A is correct
The enzymes that digest the majority of ingested fat are pancreatic lipases.
Explanation:The enzyme group that digests the majority of ingested fat is pancreatic lipases. These enzymes are produced and secreted by the pancreas and work primarily in the small intestine, where they break down dietary fats into simpler compounds like fatty acids and glycerol. This is an essential part of the digestion and absorption process for fats in our diet. The option pepsin and stomach acid refers to the digestion of proteins in the stomach, while bile salts are produced in the liver and help to emulsify fats, preparing them for digestion by lipases. The lingual lipases, meanwhile, are secreted by the salivary glands and start the digestion of fats in the mouth, but their contribution to overall fat digestion is relatively minor.
Learn more about Digestion of Fats here:https://brainly.com/question/33448886
#SPJ6
Which of the following statements is a correct explanation for the observation that all offspring exhibit a phenotype for a particular trait that appears to be a blend of the two parental varieties?
A) The genes for the trait are recessive in both of the parents.B) The genes for the trait are dominant in both of the parents.C) The genes are linked and do not separate during meiosis.D) Neither of the parental genes is dominate over the other.
Answer:
D) Neither of the parental genes is dominate over the other.
Explanation:
Since the trait on the offspring is a mixture from both parent, it means that neither of the alleles from both parents is completely dominant over the other. Instead, each of the alleles contributes equally to the trait of the offspring.
This effectively explains the fact that each trait exhibited by offspring is a blend of the traits from the two parents.
The correct option is D.
Suppose a woman with a continuous hairline and short fingers and a man with a widow’s peak and long fingers have three children. One child has short fingers and a widow’s peak, one has long fingers and a widow’s peak, and one has long fingers and a continuous hairline. What are the genotypes of the parents
Answer:
The women has a genotype of hhff and the man has a genotype of HhFf
Explanation:
From the results of the children we can see that widows peak and long fingers are dominant because it has the majority in the family. The question is are the parents homozygous dominant. The are not. They are heterozygous because if they were homozygous they wouldn’t be able to have any recessive genes transfer to the children
Pepsin is an antibacterial agent that kills some bacteria. Protease breaks down lipids into fatty acids and glycerol. Lipase breaks down proteins in the small intestine. Mucus protects the stomach lining from digestive secretions.a) trueb) false
Answer:
False,False,False,True
Explanation:
Pepsin is an antibacterial agent that kills some bacteria False.
Protease breaks down lipids into fatty acid and glycerol False.
Lipase breaks down proteins in the small intestine False.
Mucus protects the stomach from digestive secretion True.
If a double-stranded DNA sample were composed of 10% thymine, what would be the percentage of guanine?a. 10%b. 20%c. 40%d. 80%
Answer:
c. 40%
Explanation:
DNA is composed of smaller subunits called nucleotides.
Structure of a nucleotide contains a 5-carbon sugar (Deoxyribose), phosphate group and one of the four nitrogenous bases.
Adenine and Thymine are nitrogenous bases found in DNA. Other nitrogenous bases are cytosine, guanine and uracil.
Adenine, Thymine, Guanine and Cytosine are found in DNA whereas in RNA, Uracil is present instead of Thymine.
DNA is a double stranded structure.
In DNA, adenine of one strand always pairs with thymine of the other strand (complementary). Similarly, guanine of one strand pairs with cytosine of complementary strand. Adenine pairs with Thymine via 2 hydrogen bonds whereas cytosine pairs with guanine via 3 hydrogen bonds. This hydrogen bonding maintains the double helix structure of DNA.
It is implied that for every thymine present in DNA there will be adenine on the complementary stand with which it will bind via 2 hydrogen bonds.
So if a double stranded DNA sample contains 10% Thymine, then it will also contain 10% adenine. This makes the combined contribution of adenine and thymine to be 20%. The left over 80% of DNA will contain equal amounts of cytosine and guanine as each guanine binds with cytosine via 3 hydrogen bonds. So if we divide 80% into 2 equal parts then it is 40%. Hence, there is 40% guanine, 40% cytosine, 10% adenine and 10% thymine.
The percentage of guanine in a double-stranded DNA sample with 10% thymine is 40%, due to base pairing rules where adenine equals thymine and guanine equals cytosine.
Explanation:The question is focused on understanding the relationship between the different nucleotide bases in a DNA molecule. According to Chargaff's rules, the amount of adenine (A) is equal to thymine (T), and the amount of guanine (G) is equal to cytosine (C). Given that the DNA sample is composed of 10% thymine, it follows that it must also be composed of 10% adenine since A pairs with T. Therefore, since adenine and thymine together make up 20% of the DNA bases (10% + 10%), and the total amount of DNA bases must equal 100%, the remaining 80% of the bases are guanine and cytosine. Because guanine pairs with cytosine, their percentages must be equal. So, guanine and cytosine will each account for half of the remaining 80%, which is 40%. Thus, the percentage of guanine in this DNA sample is 40%.
Dna damage signaling processes are essential for regulating the ________ transition within the cell cycle.
Answer:
DNA damage signaling processes are essential foe regulating the G0 transition within the cell cycle.
Explanation:
Cell cycle is a process which prepares a cell for division.Cell cycle has various phases G0 phase,G1 phase,S phase,G2 phase and M phase.Each phase is specialized for its particular function.
Every phases of a cell cycle is under tight regulation of various proteins and this regulation is very much important to maintain the normal level of principle constituents of a cell.
DNA damage is detected by G1 cyclin CDK protein which transit the cell containing the damaged DNA into the G0 phase or quiescent phase for repair and if the damage cannot be repaired then the cell containing damaged DNA is targeted for destruction by ubiquitin pathway.
Before Muller's discovery that radiation induces mutation, scientists had to work on mutations that were found solely by phenotype differences in natural populations. Which of the features of Drosophila made it a fortuitous choice for Morgan and his colleagues?
A) having a long life cycle
B) especially high rate of mutation
C) large number of easily visible phenotypes
D) well-known biochemical pathways
E) the number of genes with only two alleles
Answer:
C) Large number of easily visible phenotypes
Explanation:
Drosophilia have large number of phenotypes, for instance have a look on different phenotypes for eye colour :
brown cinnabar garnet-2 purple rose rosy scarlet sepia vermilion white white-apricot white-eosinHow does the plasma membrane control what goes in and out of the cell
Answer: pumps, passive and active transport.
Explanation:
The plasma membrane separate the cell from external environmental, it is selectively permeable.
The plasma membrane is made of lipid bilayer. Only lipid soluble molecules can diffuse through the lipid layer. Water and ions are impermeable and require carrier mediated transport.The plasma membrane also contain integral protein that control the entry and exit of polar molecules and ions through transport mechanism.
Transport mechanism are
1. Passive transport
2. Active transport
3. Pumps
The plasma membrane regulates the movement of substances in and out of the cell through selective permeability and processes like passive and active transport. Additionally, it contains protein channels and carrier proteins that assist in the transfer of specific molecules.
Explanation:The plasma membrane, also known as the cell membrane, controls what enters and leaves the cell through its selective permeability. This means it only allows certain substances to cross it. This is achieved through various processes including passive transport (like diffusion and osmosis), where substances move from an area of high concentration to low concentration; and active transport, where the cell uses energy to move substances against their concentration gradient. Moreover, the plasma membrane also has protein channels and carrier proteins that assist in the tranportation of specific molecules.
Learn more about Plasma Membrane here:https://brainly.com/question/33587586
#SPJ6
Place the organizational levels of the ecosystem in order from most basic to most complex (base to entire system). The simplest will be on the left and the most complex on the right. Organism, Community, Population, Ecosystem Organism, Population, Ecosystem, Community Ecosystem, Community, Population, Organism Organism, Population, Community, Ecosystem
Answer: The organizational levels of the ecosystem from the basic on the left to complex;
Organism, population, community, ecosystem.
Explanation:
Organizational levels of the ecosystem show the order of level from basic to complex. It start from;
1. Organism refers to singular specie.
2. population is the total number of species occupying a geological area.
3. Community refers to group of populations of different species interacting and living together in an area.
4. Ecosystem is a community of different living species interacting with their abiotic environment.
You cross a plant that makes smooth peas with a plant that makes wrinkled peas (rr). If half of the offspring from that cross are smooth and half are wrinkled, what is the genotype of the smooth pea producing parent plant?
Answer:
Rr
Explanation:
This cross is a typical example of a test cross. A test cross is a cross between a heterozygous F1 progeny (different alleles) and a homozygous recessive parent in order to determine the actual genotype of the dominant parent i.e. whether homozygous or heterozygous dominance. In a test cross, if any of the offsprings show a recessive phenotype, it means the dominant parent is heterozygous
In this case, the allele for smooth pea (R) is dominant over that of wrinked pea (r).
If a cross between a smooth pea plant and a wrinkled pea plant gave rise to 50% phenotypical wrinkled pea plants (rr genotype, because the wrinkled shape can only express itself if it is in a homozygous state), it means that the smooth pea parent plant is heterozygous for pea shape (Rr) i.e. the allele for smooth shape was masking that of wrinkled shape in the smooth pea parent plant.
If organisms A, B, and C belong to the same class but to different orders and if organisms C, D, and E belong to the same order but to different families, which of the following pairs of organisms would be expected to show the greatest degree of structural homology?
A) A and D
B) B and D
C) B and C
D) D and E
Answer:
The right answer is D) D and E
Explanation:
All the organisms are classified into seven major groups or there are seven levels of classification in which organisms are divided. These are Kingdom, phylum, class, order, family, genus, and species.
So here kingdom is the highest level of classification and species is the lowest level of classification. So as we move from kingdom towards species the homology increase and if we move from lower to higher level the homology between organism decreases.
So as the order is at the lower level than class therefore organisms in class will show the greatest degree of structural homology therefore D and E would be expected to show higher structural homology.
The Hawaiian Islands are riding on the Pacific Plate as it moves northwest. They are being formed as the plate moves over a hot spot in the mantle. Where is the next volcano likely to form?
Answer:
I believe it would form at point D, because the volcanoes are already formed on the oldest islands so, if new ones are forming, it would lead me to believe that it would form towards the youngest mountains. I hope this helps.
Explanation:
The next volcano is likely to form at point D since it's the youngest island.
A volcano simply means a rupture in the crust of the Earth which allows hot lava, gases, and volcanic ash to escape below the surface.
Based on the diagram, the next volcano is likely to form at point D since it's the youngest island. Also, the volcanoes are already formed on the oldest islands. Therefore, the next volcano will form on the youngest island.
Read related link on:
https://brainly.com/question/12109135
Certain mutations in the regulator gene of the lac system in E. coli result in maximal synthesis of the lac proteins (β-galactosidase, etc.) even in the absence of the inducer (lactose). Provide an explanation for this observation.
Answer:
Certain mutations in the repressor gene or operator sequence make the operon constitutive.
Explanation:
Lac operon is not expressed in the absence of lactose sugar. The repressor gene codes for the repressor protein which in turn binds to the operator region. The operator region of lac operon serves as a binding site for the repressor protein. Binding of repressor to the operator region of lac operon does not allow the RNA polymerase to transcribe the genes and the expression of operon is prevented.
Certain mutations in the repressor gene or operator sequence make the operon transcriptionally active even in the absence of lactose. A mutation in the repressor gene that results in the synthesis of non-functional repressor protein or no repressor protein would make the operon constitute. Similarly, a mutation in the operator sequence that does not allow an otherwise functional repressor protein to bind it would also result in the expression of the operon in the absence of lactose.
In E. coli, mutations in the lacI gene can lead to a faulty repressor or the absence of repressor production, causing constitutive expression of lac operon genes, thus allowing the synthesis of lac proteins without the inducer lactose.
Certain mutations in the regulator gene of the lac operon can lead to the maximal synthesis of lac proteins in E. coli even without lactose, the usual inducer. The regulator gene, or lacI, normally produces an active repressor protein that binds to the operator region and prevents RNA polymerase from transcribing the lac operon genes when lactose is absent. When lactose is present, it is converted to allolactose, which binds to the repressor, altering its shape and preventing it from binding to the operator.
Mutations in the lacI gene can create a repressor protein that does not bind effectively to the operator, or none at all, leading to constitutive expression of the lac operon. Therefore, the usual regulatory control is lost, and the genes for lactose metabolism (eta-galactosidase, permease, and transacetylase) are expressed at high levels regardless of lactose presence.