Explain why heritable variation is crucial

The Founder Effect : The founder effect occurs when a portion of the population i. The founder effect is believed to have been a key factor in the genetic history of the Afrikaner population of Dutch settlers in South Africa, as evidenced by mutations that are common in Afrikaners, but rare in most other populations.

This was probably due to the fact that a higher-than-normal proportion of the founding colonists carried these mutations. The Hardy—Weinberg principle states that within sufficiently large populations, the allele frequencies remain constant from one generation to the next unless the equilibrium is disturbed by migration, genetic mutation, or selection.

Because the random sampling can remove, but not replace, an allele, and because random declines or increases in allele frequency influence expected allele distributions for the next generation, genetic drift drives a population towards genetic uniformity over time. Once an allele becomes fixed, genetic drift for that allele comes to a halt, and the allele frequency cannot change unless a new allele is introduced in the population via mutation or gene flow.

Thus even while genetic drift is a random, directionless process, it acts to eliminate genetic variation over time. Genetic drift over time : Ten simulations of random genetic drift of a single given allele with an initial frequency distribution 0. In these simulations, alleles drift to loss or fixation frequency of 0. An important evolutionary force is gene flow: the flow of alleles in and out of a population due to the migration of individuals or gametes.

While some populations are fairly stable, others experience more movement and fluctuation. Many plants, for example, send their pollen by wind, insects, or birds to pollinate other populations of the same species some distance away.

Even a population that may initially appear to be stable, such as a pride of lions, can receive new genetic variation as developing males leave their mothers to form new prides with genetically-unrelated females.

This variable flow of individuals in and out of the group not only changes the gene structure of the population, but can also introduce new genetic variation to populations in different geological locations and habitats.

Gene flow : Gene flow can occur when an individual travels from one geographic location to another. Maintained gene flow between two populations can also lead to a combination of the two gene pools, reducing the genetic variation between the two groups.

Gene flow strongly acts against speciation, by recombining the gene pools of the groups, and thus, repairing the developing differences in genetic variation that would have led to full speciation and creation of daughter species. For example, if a species of grass grows on both sides of a highway, pollen is likely to be transported from one side to the other and vice versa. If this pollen is able to fertilize the plant where it ends up and produce viable offspring, then the alleles in the pollen have effectively linked the population on one side of the highway with the other.

Species evolve because of the accumulation of mutations that occur over time. The appearance of new mutations is the most common way to introduce novel genotypic and phenotypic variance.

Some mutations are unfavorable or harmful and are quickly eliminated from the population by natural selection. Others are beneficial and will spread through the population. Whether or not a mutation is beneficial or harmful is determined by whether it helps an organism survive to sexual maturity and reproduce. Some mutations have no effect on an organism and can linger, unaffected by natural selection, in the genome while others can have a dramatic effect on a gene and the resulting phenotype.

Mutation in a garden rose : A mutation has caused this garden moss rose to produce flowers of different colors. This mutation has introduce a new allele into the population that increases genetic variation and may be passed on to the next generation. Population structure can be altered by nonrandom mating the preference of certain individuals for mates as well as the environment. Explain how environmental variance and nonrandom mating can change gene frequencies in a population.

If individuals nonrandomly mate with other individuals in the population, i. There are many reasons nonrandom mating occurs. One reason is simple mate choice or sexual selection; for example, female peahens may prefer peacocks with bigger, brighter tails. Traits that lead to more matings for an individual lead to more offspring and through natural selection, eventually lead to a higher frequency of that trait in the population. Assortative mating in the American Robin : The American Robin may practice assortative mating on plumage color, a melanin based trait, and mate with other robins who have the most similar shade of color.

You might be surprised to learn that early work in exploring the molecular basis for genetics favored proteins as the hereditary molecule instead of DNA. It was suspected that whatever was acting as a hereditary molecule would be large and complex, and proteins were both. Proteins can be very long, since they are a polymer of smaller, repeating components monomers.

Proteins are built pretty much in the same way. For proteins, the monomers are a group of compounds called amino acids each amino acid is one monomer. They also have significant differences, analogous to the different colors in the diagram: some amino acids are hydrophobic i. Some are large and bulky, others are comparatively small, and so on. Unlike the rigid bricks in our analogy, proteins are marvelously flexible, and fold up into a three-dimensional shape, as directed by the properties of the monomers.

There are 20 different amino acids that are used to make proteins, and they can be combined in any sequence in order to produce a protein with specific properties—properties that arise from the combination and specific order of amino acids, and the final shape they give to the protein.

This diversity in monomers means that there are many, many different possibilities for protein sequences and thus shapes, and functions —even a polymer only two monomers in length has possible sequences i. Beginning in the late s , however, research began to point away from proteins and towards DNA as the hereditary molecule. DNA, like proteins, is a polymer formed from a set of monomers in this case, nucleic acids. Despite this skepticism, evidence continued to mount that DNA was in fact the physical basis for hereditary information.

Once this evidence convinced the majority of scientists, the race was on to understand exactly how DNA accomplished this remarkable task. Soon, it became clear that understanding the structure of DNA was crucial to understanding its function, and several research groups famously competed to be the first to decipher it.

Determining the structure of DNA did indeed shed light on its function. Though it has only four monomers, the structure of DNA revealed how it can easily replicate and pass information on: not only is DNA a long polymer, it is a polymer that can specify its own replication through interactions between its monomers. Perhaps a picture would help explain. Imagine a DNA sequence as follows:. DNA is a pair of long polymers that can be separated and used to make new copies that are faithful to the original.

While these features of DNA readily explain how it is faithfully copied, recall that we also need to explain variation. Variation, in the most basic terms, means there is sometimes imperfection in the copying process.

Without variation, recombination would have no effect since there would be no variation to mix into new combinations. There are many ways that variation can enter during the DNA copying process, and in a future post we will examine several of them. The chromosomes now have genes in a unique combination. Independent assortment is the process where the chromosomes move randomly to separate poles during meiosis. A gamete will end up with 23 chromosomes after meiosis, but independent assortment means that each gamete will have 1 of many different combinations of chromosomes.

This reshuffling of genes into unique combinations increases the genetic variation in a population and explains the variation we see between siblings with the same parents. Visit the Learn Genetics website to go on an animated tour of the basics. Add to collection. Useful link Visit the Learn Genetics website to go on an animated tour of the basics.

Go to full glossary Add 0 items to collection. Download 0 items. Twitter Pinterest Facebook Instagram. Email Us. See our newsletters here. Deletions- lacking some important genes; parts of the chromosome are deleted. Duplications- Having more of some genes on the chromosome; there are multiples of the same genes in the sequence. Inversions- can change the nature of how genes are expressed; some genes are flipped in direction on the sequence.

Translocations- can cause some genes that aren't usually expressed to be expressed; takes genes and relocates them on the sequence. Explain why researchers originally thought protein was the genetic material. Frederick Griffith: pneumonia causing bacteria; named unknown factor the "transforming principle". Alfred Hershey and Martha Chase: nucleic acids, not proteins, are the heredity material, at least for viruses.

E rwin Chargaff: nucleotide composition in many organisms is same. X-ray diffraction crystallography; they used what they knew from Chargoff and other scientists as evidence. Rosalind Franklin took photograph 51 using x ray crystalography process which showed double helix nature of dna as well as the spacing between "steps of ladder".

DNA as we know it to be, is a double helix and is made up of nucleotides. Each nucleotide comprises a 5-carbon sugar, a nitrogenous base and a phosphate group. Guanine always bonds to Cytosine and Adenine to Thymine. In RNA however, the base thymine is replaced with Uracil.

The main significance of base pairing is to enable the maintanance of the gene pool within a species. The significance of base pairing: to maintain genetic stability and the genetic characteristics that pass on to the offspring of a species. Starts at origin of replication which is a sequence that have a specific sequence of nucleotides which tells it where to begin.

Proteins that initiate DNA replication recognize sequence, bind to it and separate the strands and open up replication bubble.

Goes in both directions until the entire molecule is copied. At the end of each bubble is a replication fork, the region where the strands are being unwound. They catalyze the synthesis of new DNA by adding nucleotides to a reexisting chain. It also proofreads the copies and fixes them to make correct sequence. Loss of the two phosphates; splitting pyrophosphate from the uncoming nucleotide. Leading Strand: is synthesized in the same direction as the movement of the replication fork and is synthesized continously.

Lagging Strand: is synthesized in the opposite direction and must be done in a series of segements Okazaki fragments and loop outward in order to replicate. Synthesized discontinuously in Okazaki fragments. Each fragment must be primed seperately. Then DNA ligase bonds the fragments. It can only add to the 3' end because it results in elogation of the new strand in 5' to 3' direction. Joins 3' end of DNA that replaces primer to the rest of the leading strand and joins Okazaki fragments on lagging strand.

The two strands of DNA run in different directions. One is 5' to 3', the other is the reverse. Replication can only occur from 5' to 3'. So the strand running 3' to 5' must be done in pieces running from 5 to 3 in fragments. Mismatch repair enzyme remove and replace incorrectly paired nucleotides.

Nuclease in DNA proofreading and repair: cuts out the damaged DNA strand and then it fills the gap with nucleotides using the undamaged strand. In interphase, the chromatin is highly extended. Preparing for mitosis, the chromatin coils or condenses and forms chromosomes in metaphase. The r ibosome reads the code on the RNA strand translation , and creates a protein from strand. Translation- synthesis of a polypeptide, which occurs under the direction of mRNA.

Bacteria can do it at the same time; lack nucleus so it occurs in cytolplasm. Eukaryotes need transcription factors, a 5' cap and 3' tail, extra proteins and the ribosomes are different; Transcription is in the nucleus and translation is in ribosomes. Because codons are base triplets, the number of nucleotides making up the genetic message must be three times the number of amino acids in the protein product. The start codon t hat signals where a polypeptide chain should start is AUG or Met which is always the start codon.

I t specifies which of the possible reading frames of a sequence will be translated. Each reading frame can encode a different amino acid sequence and, thus, a different protein. Elogation: RNA polymerase will unwind and add nucleotides until it reaches the terminator.

Termination: comes to the terminator and will release the completed RNA. Explain why, due to alternative RNA splicing, the number of different protein products an organism can produce is much greater than its number of genes.

Many genes are known to give rise to two or more different polypeptides , depending on which are exons. One gene can encode for more than one kind of polypeptide. Have sites A, P, and E. At the start of translation, the ribosome positions itself over the mRNA tape so as to expose to the A site the codon on the tape that represents the next amino acid due to be added to the chain. Goes then to the E site and o nce released, an appropriate aminoacyl-tRNA synthetase enzyme attaches to the deacylated tRNA, adds the appropriate amino acid.

A, P, and E. Describe the process of translation including initiation, elongation, and termination and explain which enzymes, protein factors, and energy sources are needed for each stage. Elongation: new tRNA in A site; form peptide bond between P site peptides and A site peptide; peptide chain that lost peptide exits and another moves into P site. Hydrolyze 2 GTP.

Termination: Release factor will come form base pairs with stop codon, freeing peptide and then it stops. A gene determines the primary structure, which then determines the shape. It can be modified by the attachments of sugars, lipids, phosphate groups, or others. Some remove one or more amino acids from the leading end of the polypeptide chain. The signal sequence found at the start of a protein being coded by the ribosome alerts the ribosome to attach itself to the ER. If the sequence is missing it will remain free.

Base pair substitiution - replacement of one nucleotide and its partner with another pair of nucleotides. Base pair insertion - additons of nucleotide pairs in a gene. Frameshift- addition of an extra A wgich can create stop codon early. Why is an insertion or deletion more likely to be deleterious than a substitution? They shift the whole sequence which could cause extensive missense whereas a codon can just change with substitutions.

Give an example of a physical and a chemical agent of mutation. Shared Flashcard Set. Title BIO Description 3rd Exam. Total Cards Subject Biology. Level Undergraduate 1. Create your own flash cards! Sign up here. They are control mechanisms that ensure the fidelity of cell division in eukaryotic cells. These checkpoints verify whether the processes at each phase of the cell cycle have been accurately completed before progression into the next phase.

Supporting users have an ad free experience! Flashcard Library Browse Search Browse. Create Account. Additional Biology Flashcards. Term Explain how cell division functions in reproduction, growth, and repair. Definition As cells divide, they differentiate into different types of cells. Term Describe the structural organization of a prokaryotic and eukaryotic genome.

Definition Prokaryotic- cell division is for reproduction Eukaryotic- reproduction and sexual reproduction. Term Describe the major events of eukaryotic cell division that enable the genome of one cell to be passed on to two daughter cells. Definition The DNA is copied and then two copies separated so that each daughter cell ends up with a complete genome. Term List the phases of the cell cycle and describe the sequence of events that occurs during each phase.

Term List the phases of mitosis and describe the events characteristic of each phase. Definition Prophase - mitotic spindle formed, centrosomes migrate to cell poles, chromosomes condense, nuclear membrane fragments, and metabolic activity decreases. Telophase - chromosomes decondense and nuclear membrane starts to form Cytokinesis - division of cytoplasm right after or during telophase. Term Describe the changes in the mitotic spindle during each phase of mitosis.

Definition Prophase - formed Metaphase - pull the chromosomes toward the metaphase plate Anaphase - pull the chromosomes apart and to opposite poles and disintegrate Telophase - not present.

Term Explain how nonkinetochore microtubules lengthen the cell during anaphase. Definition Nonkinetichore microtubules elongate stretching the cell, making it longer and pull the chromosomes apart to opposite poles. Term Compare cytokinesis in animals and plants. Definition Animals - the membrane pinches to separate Plants - a plate is formed between the two. Term Describe the process of binary fission in bacteria. Definition Bacteria cells split into two halves.

Term Distinguish between benign, malignant, and metastatic tumors.