Unit 5, 6, and 7

Difference Between Meiosis and Mitosis!

• You need to understand the difference between mitosis and meiosis. They’re similar, but:

• Mitosis: makes more body or SOMATIC cells.• Meiosis: Makes more sex cells or gametes.

• Meiosis: a form of cell division that halves the number of chromosomes when forming specialized reproductive cells, such as gametes or spores.– There are two stages of meiosis, Meiosis I and

Meiosis II– In animals, meiosis produces haploid gametes or sex

cells, sperm and eggs

Formation of Haploid Cells• Before the process of meiosis, like mitosis, the DNA

replicates.• This makes a cell with how many chromosomes?

• There are 8 stages in Meisois, and they should sound familiar:

MEIOSIS I:•Prophase I•Metaphase I•Anaphase I•Telophase I and cytokinesis

MEIOSIS II:•Prophase II•Metaphase II•Anaphase II•Telophase II and cytokinesis

Meiosis I

Meiosis II

Crossing-Over and Random Fertilization

• DNA exchange during crossing over in Prophase I adds even more recombination to the independent assortment of chromosomes, making even MORE genetic combinations!

Crossing-Over: a type of genetic recombination that occurs when portions of a chromatid on one homologous chromosome are broken and exchanged with the corresponding chromatid, increasing genetic diversity.

•Meiosis, gamete-joining, and crossing-over are essential to evolution because these processes generate genetic variation very quickly.•The pace of evolution is sped of by genetic recombination!

Sexual and Asexual Reproduction

• Some organisms have two parents, other only have one.

• Reproduction can be sexual or asexual. • Sexual Reproduction: two parents form reproductive

cells that have one-half the number (haploid) of chromosomes which combine to make a diploid individual.

• Asexual Reproduction: a single parent passes copies of all its genes to each of its offspring—no fusion of haploid cells such as gametes. – Clone: an organism that is genetically identical to its parent.

Hypotheses for Heredity • Prior to Mendel’s work, people thought offspring

were a blend of their parents.• Mendel’s work did not support the blending

hypothesis.• Mendel concluded that each pea had two separate

“heritable factors” for each character—one from each parent.– When sperm and eggs (gametes) form, each receives

only one of the organism’s two factors for each character.– When the gametes fuse, each offspring has two factors

for each character.

Mendel’s Hypotheses

1. For each inherited character, an individual has two copies of the gene—one from each parent.

2. There are alternative versions of genes—a pea plant can have a purple version or a white version.– Allele: the different

versions of a gene

Mendel’s Hypotheses 3. When two different alleles occur

together—one of them may be completely expressed, while the other may have no observable effect on the organism’s appearance.– Dominant: the expressed form of

the character– Recessive: the trait not expressed

when the dominant form is present.

Mendel’s Hypotheses• 4. When gametes are

formed, the alleles for each gene in an individual separate independently of one another. Thus, gametes carry only one allele for each inherited character. When gametes unite during fertilization, each gamete contributes one allele.

Mendel’s Findings in Modern Terms

• Dominant Traits: Capital letter• Recessive Traits: lower case letter• Pea Plants:–Purple—Dominant: P (capital P)–White—Recessive: p (lowercase p)

• Homozygous: if the two alleles of a particular gene are the same in an individual

• Heterozygous: if the two alleles of a particular gene are different in an individual

Mendel’s Findings in Modern Terms

• Genotype: the set of alleles that an individual has for a character.–The genes they actually

have.• Phenotype: the physical

appearance of a character.–How they look.

The Laws of Heredity • The Law of Segregation: the two alleles for a

character segregate (separate) when gametes are formed.– This is the behavior of chromosomes during meiosis.

• The Law of Independent Assortment: The alleles of different genes separate independently of one another during gamete formation. – The inheritance of one character does not influence the

inheritance of another, as long as they’re on separate chromosomes!

Punnett Squares• Punnett

Square: A diagram that predicts the outcome of a genetic cross by considering all possible combinations of gametes in the cross.

Inheritance • Dominant: If the gene is autosomal dominant,

every individual with the condition will have a parent with the condition.

• Recessive: If the condition is recessive, an individual with the condition can have one, two, or neither parent exhibit the condition.

• Heterozygous/Homozygous: If individuals with autosomal traits are homozygous dominiant or heterozygous, their phenotype will show the dominant allele. If individuals are homozygous recessive, they will show the recessive allele.

Autosomal or Sex-Linked

• Autosomal: gene occurs on an autosome. – If a trait is autosomal, it will appear in both sexes

equally. • Sex-Linked: gene occurs on an X or Y chromosome. – A female with a recessive trait will only show it if it

occurs on both of her X chromosomes.– Thus, males are more likely to exhibit sex-linked

recessive traits.

Complex Control of Characters• Patterns of heredity are complex. Most of the time,

characters display more complex patterns of heredity than the simple dominant-recessive patterns discussed so far.

• Characters can be influenced by several genes.– It isn’t always as easy as Punnett squares make it seem!– Polygenic inheritance: when several genes influence a

character. • Determining the effect of any one of these genes can be difficult.

Due to crossing-over and independent assortment, many different combinations appear in offspring.

• Familiar examples of polygenic traits include eye color, hair color, skin color, height, and weight.

Intermediate Characters

• In Mendel’s pea-plants, one allele was dominant over another. Sometimes, however, there is an intermediate between the two parents.

• Incomplete Dominance: an individual that displays a phenotype that is intermediate between two parents.– In snapdragons (on right), the flowers in

a cross between red and white parents appear pink because neither the red or white allele is completely dominant over the other allele.

Genes with 3 or more Alleles• Multiple Alleles:

Genes with three or more alleles.

• Example: ABO Blood Groups are determined by three alleles:– IA, IB, i– IA and IB are both

dominant over I– Combinations of

these three alleles makes four blood groups.

Codominance • Codominance: Both

traits are displayed at the same times.

• Example: AB Blood Group—A and B are both dominant traits, and if someone has both alleles they have an AB blood type.

Decoding the Information in DNA

• Gene: A segment of DNA in a chromosome that codes for a particular protein.

• Traits such as eye color are determined by proteins built according to instructions coded in genes in the DNA.

• Proteins are not built directly from DNA. RNA is also involved.

• RNA=Ribonucleic Acid• Three Differences between DNA and RNA– RNA is singled stranded rather than double stranded.– RNA has ribose sugar rather than deoxyribose sugar.– RNA has Uracil (U) rather than Thymine (T) bases. U pairs

with A. Buck 2011

Decoding the Information in DNA

• A gene’s instructions for making a protein are coded in the sequence of nucleotides in the gene. The instructions for making a protein are transferred from a gene to RNA in a process called transcription.

• Transcription: Making RNA using one strand of DNA as a template.• Translation: in ribosomes, when mRNA (messenger RNA) molecules

are used to specify the sequence of amino acids in polypeptide chains (precursors of proteins)

Gene Expression: The manifestation of the genetic material of an organism in the form of specific traits.

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Transcription: Making RNA

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The Genetic Code: Three-Nucleotide “Words”

• Different types of RNA are made during transcription, depending on the gene being expressed.

• When a cell needs a particular protein, mRNA (messenger RNA) is made.

• Messenger RNA (mRNA): a form of RNA that carries the instructions for making a protein from a gene and delivers it to the site of translation.

• The information from mRNA is translated from the language of RNA (nucleotides) to the language of proteins (amino acids).

• The RNA instructions are written as a series of three-nucleotide sequences on the mRNA called codons.

• Each codon along the mRNA strand corresponds to an amino acid or signifies a start of stop signal for translation.

RNA’s Roles in Translation

• Transfer RNA (tRNA) molecules and ribosomes help in the synthesis of proteins.

• Transfer RNA (tRNA): single strands of RNA that can carry a specific amino acid on one end, folds into a compact shape and has an anticodon.– Anticodon: a three-nucelotide sequenceo n a tRNA that is complementary to

an mRNA codon. • Ribosomal RNA (rRNA): RNA molecules that are part of the structure of

ribosomes.

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Protein Synthesis in Prokaryotes

• Operator: piece of gene that controls RNA polymerase’s access to the genes.

• An operon is a group of genes that code for enzymes involved in the same function…this is the lac operon.

• Repressor: is a protein that binds to an operator and physically blocks RNA polymerase from binding and strops transcription.

When lactose is present, the lactose binds to the repressor and changes the shape of the repressor. The change in shape causes the repressor to fall off of the operator. Now the

bacterial cell can begin transcribing the genes that code for the lactose-metabolizing enzymes. Buck 2011

Controlling the Onset of Transcription

• Eukaryotic cells have more DNA than prokaryotic cells therefore there are more opportunities for regulating gene expression.

• Transcription factors: help arrange RNA polymerase in the correct position on the promoter– Enhancer: can be bound by an activator away from the gene

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Intervening DNA in Eukaryotic Genes

• In eukaryotes, a gene is not an unbroken stretch of nucleotides.

• Many genes are interrupted by introns.

• Intron: long segments of nucleotide that have no coding information.

• Exons: portions of a gene that are translated.

• This adds options to evolution!appropriately joined

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Karyotype• Karyotype: number of

Chromosomes in a cell• 22 pairs of autosomes, 1 pair of

sex chromosomes• 44 autosomes total, 2 sex

chromosomes total• XX=female• XY=male• Can be used to identify gender

and chromosomal disorders.• Incorrect chromosome numbers

are caused by nondisjunction of chromosomes in meiosis—meaning that the chromosomes do not separate correctly.

Chromosome Disorders

• Sex Chromosome Disorders: – Klinefelter’s syndrome (XXY)– Triple X Syndrome (XXX)– Turner’s Syndrome (XO)– Jacob’s Syndrome (XYY)

• Autosomal Disorders: – Down Syndrome (Trisomy 21)– Monosomy 21– Patau’s Syndrome (Trisomy 13)– Edward’s Syndrome (Trisomy 18)– Cri du Chat (partial deletion of chromosome 5)

The Evolution of Prokaryotes

Scientists use fossils to study evidence of early life on Earth. Fossil: the preserved or mineralized

remains or imprints of an organism that lived long ago.

The oldest fossils are 3.5 billion year old prokaryotes.

Some of the first prokaryotes were marine cyanobacteria. Cyanobacteria: photosynthetic

prokaryotes Helped release oxygen gas into oceans,

and eventually the air. Buck 2011

http://www.mbari.org/staff/conn/botany/phytoplankton/phytoplankton_cyanobacteria.htm

http://www.dkimages.com/discover/Home/Plants/Fungi-Monera-Protista/Cyanobacteria/Cyanobacteria-2.html

The origins of Mitochondria and Chloroplasts

Most biologists think that mitochondria and chloroplasts originated as described by the theory of endosymbiosis. Theory of Endosymbiosis: mitochondria are the descendants

of symbiotic, aerobic eubacteria and chloroplasts are the descendants of symbiotic, photosynthetic eubacteria Bacteria entered larger cells, and began to live inside the cell

performing either cellular respiration or photosynthesis.

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Other Organelles The folding in the plasma membrane may have been the

forerunner of both the endoplasmic reticulum and nuclear envelope based on similar structure and biochemical analysis.

Part of cell specialization: a process where cells become modified to perform specific functions in an organism.

Buck 2011

http://en.wikibooks.org/wiki/Structural_Biochemistry/Cell_Organelles/Endoplasmic_Reticulum#Smooth_Endoplasmic_Reticulum_.28SER.29http://picsbox.biz/key/rough%20endoplasmic%20reticulum%20function

Multicellularity• Protists were the first eukaryotes. Protists

make up a large varied group of both multicellular and unicellular organisms.

• Unicellular organisms are very successful, but each cell must carry out all the activities of the organism.

• Distinct types of cells in one body can have specialized functions (like in your immune system, for example).

• Almost every organism you can see without a microscope is multicellular.

• Fossils of the first multicellular organisms are about 700 million years old.

A singled celled protist

Multicellular protists—

brown algaeBuck 2011

http://bio.rutgers.edu/~gb101/lab6_protists/m6a.html

http://sopastrike.com/strike

Mass Extinction and Continental Drift Continental drift also played an

important role in evolution. Continental Drift: the

movement of Earth's land masses over Earth’s surface through geologic time. Resulted in present-day position of the continents. Helps to explain why there are a

large number of marsupials in both Australia and South America, because these continents were once connected.

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The fossil record indicates that a sudden change occurred at the end of the Ordovican period—a large percentage of organisms became extinct. Extinction: the death of all members of a species.Mass Extinction: an episode during which large numbers of species becomes extinct. Mass extinctions can allow new species to adapt and fill niches previously occupied by the now-extinct species, and thus help drive evolution.

The Ozone Layer While the sun gives us the light energy Earth’s organisms need, it also

produces dangerous ultraviolet (UV) radiation. Early life lived in the sea, which protected it from dangerous UV radiation.

However, land organisms needed protection. This protection is provided in the upper atmosphere by the ozone layer

which blocks UV radiation. The Ozone (O3—regular oxygen is O2layer formed about 2.5 billion years

ago as cyanobacteria began adding oxygen to the earth’s atmosphere.

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Darwin’s Observations On his voyage, Darwin found evidence challenging the

belief that species do not change. Darwin read Charles Lyell’s book Principles of Geology

which proposed that the surface of Earth changed slowly over many years.

Darwin saw things that could be explained only by a process of gradual change. In South America, he found fossils of extinct armadillos which

were similar but not identical to modern armadillos in the area. Darwin visited the Galápagos Island and noticed that the

species on the islands were similar to those from South America, but they changed since they arrived.Darwin called this Descent with modification, or evolutionBuck

2011

Evolution by Natural Selection

Darwin called this differential rate of reproduction Natural Selection.In time, the number of individuals

that carry inherited favorable characteristics will increase, and the population will change or evolve!

Organisms differ from place to place because their habitats are different, and each species has reacted to its own environment. Adaptation: An inherited trait that

has become common in a population because the trait provides a selective advantage. Buck

2011

http://goose.ycp.edu/~kkleiner/ecology/EvolEcologyimages.htm

Darwin’s Four Major Points1. Inherited variation exists within the genes of every population or

species (the result of random mutation and translation errors). Or: Not every organism is identical!

2. In a particular environment, some individuals of a population or species are better suited to survive (as a result of variation) and have more offspring (natural selection).

Or: Some organisms do better and have more babies!

3. Over time, the traits that make certain individuals of a populations able to survive and reproduce tend to spread in that population.

Or: Organisms that do better give their advantages to those babies they had!

4. There is overwhelming evidence from fossils and many other sources that living species evolved from organisms that are extinct. Buck

2011

Change Within Populations• Darwin’s ideas were based on the idea that in any

population, individuals that are best suited to survive will produce the most offspring. These traits will become common new generations.

• Scientists now know that genes are responsible for inherited traits. Certain forms of genes called alleles become more common.– In other words: natural selection causes the allele

frequency to change.• Mutations and sexual reproduction provide the

variation needed for natural selection. – Random gene mutation is essential to evolution! Buck

2011

The Fossil Record• Fossils offer the most direct

evidence that evolution takes place—fossils of animals show a pattern of development from ancestors to modern descendants.

• Fossils provide a record of Earth’s past life-forms.

• Evolution: Change over time. – Evolution can be observed in

the fossil record. Buck 2011

Anatomy and Development Comparisons of anatomy of different types of organisms often reveal

basic similarities in body structures even though the function may differ between organisms.

Vestigial Structure: a structure in an organism that is reduced in size and function and that may have been complete and functional in the organism’s ancestors.

Similarities in bone structure can be seen in vertebrates, suggesting they have a relatively recent common ancestor

Homologous Structures: structures that share a common ancestry. Similar structure in two organisms can be found in the common ancestor of the organisms. Example: human arm, monkey arm

Analogous Structures: are features of different species that are similar in function but not necessarily in structure and which do not derive from a common ancestral feature (compare to homologous structures) and which evolved in response to a similar environmental challenge. Example: bird wing, insect wing

Evolutionary history of organisms is also seen in the development of embryos. The stages of embryonic development are similar in many species. Buck

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Homologous Structures

Proteins and DNA Sequence• Amino acid sequences of similar proteins were

compared. • If evolution has taken place, then species descended

from a recent common ancestor should have fewer amino acid differences in proteins than do species that aren’t as closely related.

This pattern does not hold true for all proteins. A certain protein may evolve more rapidly in some groups than others.

Comparisons of proteins may not reflect evolutionary relationships supported by the fossil record and other evidence.

More accurate hypotheses about evolutionary histories are based on large numbers of gene sequences.

These evolutionary histories based on DNA sequences tend to be similar to those from the fossil record.

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Examples of Natural Selection

Tuberculosis (TB) is caused by the bacterial species M. tuberculosis and kills more adults than any other infectious disease in the world.

Two effective antibiotics because available to fight this bacteria.

However, in the late 1980s, new strains of Tuberculosis that are resistant to the antibiotics appeared.

These resistant bacteria evolved through natural selection.

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Gene Pools Natural selection utilized the diversity in a species’ gene pool. Gene Pool: The total number of genes of every individual in an

interbreeding population.Gene pools contain variations in genes, relative gene frequencies, and

allele frequencies. Genetic recombination can influence the gene pool and variation.

Variations: A modification in structure, form, or function. Relative Frequency: the average number of occurrences of a

particular event in a large number of repeated trials. Allele Frequency: the frequency of an allele compared to other

alleles of the same gene in a population. Natural selection makes the most successful alleles (different

copies of genes) most common in a population. In this way, natural selection changes the POPULATION, not the

INDIVIDUALS! Buck 2011

Formation of New Species Species formation occurs in stages. A species molded by natural selection

has an improved “fit” to its environment.

Divergence: The accumulation of differences between groups. Divergent (split apart) Evolution: The

process by which an interbreeding population diverges (splits) into two or more descendant species, resulting in once similar or related species to become more and more different.

Convergent (come together) Evolution: A kind of evolution wherein organisms evolve parts that have similar structures or functions in spite of their evolutionary ancestors being very dissimilar or unrelated.

Speciation: The process by which new species form.

The body structure of these organisms are examples of

convergent evolution. http://bio1152.nicerweb.com/Locked/media/ch40/

fast_swimmers.html

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Resources and Population Size• As a population grows, limited

resources eventually become depleted and population growth slows.

• The Logistic Model: A population model in which exponential growth is limited by a density-dependent factor.– Density-Dependent factor:

limited resources that become depleted when the population is larger.

Exponential Growth Curve:

Also called a j-curve

Also called an s-curve

Logistic Growth Model:

Growth Patterns in Real Populations

• Exponential Growth Patterns are best to describe faster growing organisms such as:– Many plants– Insects

• Logistic Growth Model is best to describe slower growing organisms such as:– Bears– Elephants– Humans

• Density-Independent Factors: environmental conditions– Weather– Climate

Exponential Growth Curve:

Also called a j-curve

Also called a j-curve

Logistic Growth Model:

Also called an s-curve

Rapidly and Slowly Growing Populations• r-strategists: grow

exponentially when environmental conditions allow them to reproduce.– Results in temporarily large

populations.• When environmental conditions

are good, the population grows rapidly. When conditions are poor, the population size drops quickly.

• Generally r-strategists:– Have a short life span– Reproduce early– Many small offspring– Offspring mature with little

parental care

K-strategists: organisms that grow slowly with small population sizes and a population density usually near the carrying capacity (K) of their environment.Generally K-strategists:

Have a long lifeMature slowlyHave few youngProvide extensive care for young

Allele Frequencies • Allele Frequency: the frequency of an allele compared to

other alleles of the same gene in a population. – Biologists began to study how allele frequency changed in

populations and wondered if dominant alleles (usually more common than recessive) would spontaneously replace recessive alleles in populations.

• Hardy and Weinberg demonstrated that dominant alleles do not automatically replace recessive alleles.– They showed that the frequency of alleles in a population does

not change. – Also, the ratio of heterozygous individuals to homozygous

individuals does not change unless the population is acted on by something that favors a particular allele.

The Hardy-Weinberg Principle• Hardy-Weinberg Principle: allele frequencies in a population do

not change unless evolutionary forces act on the population. • Hardy-Weinberg Equation: p2+2pq+q2=1• When no evolutionary forces are acting on a population, it is in:

– Genetic Equilibrium: A relative measure of reproductive success of an organism in passing its genes to the next generation.

• There are five principal evolutionary forces that can cause genotype ratios to change:1. Mutation2. Gene Flow3. Nonrandom Mating4. Genetic Drift5. Natural Selection

Five Principle Evolutionary Forces (Cause Genetic Change in a Population)• Mutation: source of variation and makes evolution possible.• Gene Flow: the movement of alleles into or out of a

population. Occurs because new individuals (immigrants) add alleles and Departing individuals (emigrants) take alleles away.

• Nonrandom Mating: when individuals prefer to mate with others that live nearby, or are of their own phenotype, or based on certain traits.

• Genetic Drift: the random change in allele frequency in a population.

• Natural Selection: Causes deviations from Hardy-Weinberg by directly changing allele frequencies, since some alleles are being selected for.