Module 2 Review

The main stages of the cell cycle are: Gap 1, Synthesis, Gap 2, & Mitosis.

• Gap 1 (G1): cell growth and normal functions, copy organelles (most cells spend most of their time here)– Only proceed to S if the cell has enough nutrition, adequate

size, undamaged DNA

• Synthesis (S): copies DNA• Gap 2 (G2): additional growth• Mitosis (M): includes division of the cell nucleus

(mitosis) and division of the cell cytoplasm (cytokinesis)– Mitosis occurs only if the cell is large enough and the DNA

undamaged.

Cell size is limited.• Cell volume increases faster than surface

area.– Cells need to stay small to allow diffusion and

osmosis to work efficiently.

Chromosomes condense at the start of mitosis.

• Chromosomes: carry genetic information (DNA) that is passed from one generation of cells to the next.

• DNA wraps around proteins (histones) that condense it.

• DNA plus proteins (histones) is called chromatin.

• Each chromosome is composed of two chromatids

• Sister chromatids are held together at the centromere.

• Telomeres protect DNA and do not include genes (like the caps on shoelaces)

Mitosis and cytokinesis produce two genetically identical daughter cells.

• Interphase prepares the cell to divide.

• DNA is duplicated.

Mitosis divides the cell’s nucleus in four phases - PMAT

• Prophase – first & longest– Chromosomes condense, spindle fibers

form, and the nuclear membrane disappears.

Mitosis divides the cell’s nucleus in four phases.

• Metaphase–Chromosomes line up across the

middle of the cell.

Mitosis divides the cell’s nucleus in four phases.

• Anaphase–Sister chromatids are pulled apart

to opposite sides of the cell.

Mitosis divides the cell’s nucleus in four phases.

• Telophase– Two nuclei form at opposite ends of the

cell, the nuclear membranes reform, and the chromosomes uncoil back into chromatin

Cytokinesis differs in animal and plant cells.

• Cytokinesis is when the cytoplasm separates

– Animal cells: membrane pinches the two new cells apart

– Plant cells: a cell plate (new cell wall) separates the two new cells

Cell division is uncontrolled in cancer.• Cancer cells form disorganized clumps called

tumors.– Benign tumors remain clustered and can be

removed.– Malignant tumors metastasize, or break away, and

can form more tumors.

• Cancer cells do not carry out normal cell functions (this is part of why they’re so bad!)

• Cancer cells come from normal cells with damage to genes involved in cell-cycle regulation.

• Carcinogens are substances known to cause cancer (they damage those genes)– Chemicals, tobacco smoke, X-rays, UV rays, HPV

• Cancer can also be caused by genetics (i.e. BRCA1)• Standard cancer treatments typically kill both cancerous and

normal, healthy cells.

Apoptosis is programmed cell death.• Apoptosis is the process of programmed cell

death.– Normal feature in healthy organisms

Binary fission is similar to mitosis.• Asexual reproduction is the creation

of offspring from a single parent.– Pros: more efficient in favorable

environments.– Cons: All respond to environment identically– Binary fission produces two daughter cells

genetically identical to the parent cells.– Binary fission occurs in prokaryotes.

– Some eukaryotic cells also reproduce asexually via mitosis – budding, fragmentation, vegetative reproduction

Multicellular organisms depend on interactions among different cell types.• Tissues are groups of cells that perform a similar

function.• Organs are groups of tissues that perform a specific

or related function.• Organ systems are groups of organs that carry out

similar functions.

Specialized cells perform specific functions.

• Cells develop into their mature forms through the process of cell differentiation.

• Cells differ because different combinations of genes are expressed.

You have somatic cells and gametes.

• Somatic Cells:– Are body cells– Make up all cells in body except for

egg and sperm cells– DNA not passed on to children

• Gametes:– Are egg or sperm cells– DNA passed on to children

Your cells have autosomes and sex chromosomes.

• Human somatic cells have 23 pairs of chromosomes (46 total)– (1) Autosomes: pairs 1 – 22; carry

genes not related to the sex of an organism

– (3) Sex chromosomes: pair 23; determines the sex of an animal; control the development of sexual characteristics

– (2) Homologous chromosomes: pair of chromosomes; one from each parent; carry the same genes but may have a different form of the gene (example: one gene for brown eyes and one gene for blue eyes)

Somatic cells are diploid; gametes are haploid.

• Diploid (2n)– Has two copies of each

chromosome (1 from mother & 1 from father)• 44 autosomes, 2 sex

chromosomes– Somatic cells are diploid– Produced by mitosis

• Haploid (1n)– Has one copy of each

chromosome• 22 autosomes, 1

sex chromosome– Gametes are haploid– Produced by meiosis

• Meiosis makes different haploid cells from diploid cells, reduces chromosome number & increases genetic diversity.

• Homologous chromosomes (sometimes called homologues)– Pair of chromosomes– Inherit one from each parent– Carry same genes but code for different traits (different versions

of the gene)– Separate during Meiosis I

• Sister chromatids– Duplicates of each other– Each half of a duplicated chromosome– Attached together at the centromere– Separate in Meiosis II

Meiosis I• Occurs after DNA has been replicated

(copied)• Divides homologous chromosomes in four

phases.

Meiosis II• Divides sister chromatids in four phases.• DNA is not replicated between Meiosis I and

Meiosis II.• Ends in 4 genetically different cells

Mitosis Vs. Meiosis

Mitosis• One cell division• Homologous chromosomes

do not pair up• Results in diploid cells• Daughter cells are identical

to parent cell

Meiosis• Two cell divisions• Homologous chromosomes

pair up (Metaphase I)• Results in haploid cells• Daughter cells are unique

Haploid cells develop into mature gametes.

• Gametogenesis is the production of gametes.• Gametogenesis differs between males and

females.– Sperm (spermatogenesis)

• Become streamlined and motile (able to move)• Primary contribution to embryo is DNA only

– Egg (oogenesis)• Contribute DNA, cytoplasm, and organelles to the

embryo• During meiosis, the egg gets most of the contents, the

other 3 cells become polar bodies

Sexual reproduction creates unique combinations of genes.

• Fertilization– Random– Increases unique combinations of genes

• Independent assortment of chromosomes– Homologous chromosomes line up randomly

along the cell equator– Increases the number of unique combinations of

genes

Sexual reproduction creates unique combinations of genes.• Crossing over

– Exchange of chromosome segments between homologous chromosomes

– Increases genetic diversity– Occurs during Prophase I of Meiosis I– Results in new combinations of genes (chromosomes

have a combination of genes from each parent)

Genetic linkage• Chromosomes contain many genes.

– The farther apart two genes are located on a chromosome, the more likely they are to be separated by crossing over

• Genetic linkage: genes located close to each other on the same chromosome tend to be inherited together

The same gene can have many versions.

• A gene is a piece of DNA that directs a cell to make a certain protein.

• Each gene has a locus, aspecific position on a pair ofhomologous chromosomes.

• An allele is any alternative form of a gene occurring at a specific locus on a chromosome. (gene=pea shape, alleles= wrinkled or smooth)– Each parent donates one

allele for every gene.– Homozygous describes

two alleles that are the same at a specific locus. Ex: (RR or rr)

– Heterozygous describes two alleles that are different at a specific locus.Ex: (Rr)

– A dominant allele is expressed as a phenotype (visible trait) when at least one allele is dominant.

– A recessive allele is expressed as a phenotype (visible trait) only when two copies are present.

• Practice: Ff x ff• What words would you use to describe the P generation (parents)?• What would the phenotype and genotype be of the F1 generation?

Phenotype: 50% Purple, 50% White

Genotype: 50% Heterozygous, 50% Homozygous Recessive

• Mendel drew three important conclusions.

1. Traits are inherited as discrete units.2. Organisms inherit two copies of each gene, one from each parent.3. The two copies segregateduring gamete formation.– The last two conclusions are

called the law of segregation.purple white

Incomplete Dominance = BLENDING in heterozygotes

• Neither allele is dominant over the other, so individuals with a heterozygous genotype show a blended phenotype somewhere in the middle. (i.e. red + white=pink)

• Use different letters to represent each possible allele (instead of Rr use RW since there is not dominant or recessive allele)

• Examples: feather color in chickens, flower color such as roses or snapdragons.

Phenotype ratio: 100% PinkGenotype ratio: 100% heterozygous

Co-dominance = TOGETHER or SPOTTED – both traits are FULLY and SEPARATELY expressed • Co means together, and BOTH alleles are

dominant so they show up together. Ex: hair color in humans, fur color in cattle.

• Use different letters to represent each possible allele (instead of Bb use BW since there is not dominant or recessive alleles)

BB BW

BW WW

B W

B

W

Phenotype: 25% Black, 25% white, 50% black and white Genotype: 25% homozygous black, 25% homozygous white,

50% Hetero

Sex-Linked Inheritance• Some disorders are carried on the X

chromosome. Examples of these disorders are color blindness, and hemophilia.

• Only females can be carriers (heterozygous) because they have two X chromosomes

• Males either have the allele (and hence show the trait) or they don’t. Males only get 1 X, so whatever they inherit on that 1 X is what you see.

Phenotype: 50% Normal vision females 25% Normal vision males25% Color Blind males Genotype: 25% XBXb (Carrier) 25% XbY 25% XBXB 25% XBY

Human Blood Types: Use both co-dominance and regular dominant/recessive. • A and B are co-dominant. O is recessive.• Use the chart to help with crosses.

DNA is composed of four types of nucleotides.

*DNA is a double helixDNA is made up of a long chain of nucleotides.Each nucleotide has three parts.

– a phosphate group– a deoxyribose sugar– a nitrogen-containing base

phosphate group

deoxyribose (sugar)

nitrogen-containingbase

TACG

Nucleotides always pair in the same way.

• The base-pairing rules show how nucleotides always pair up in DNA.– A pairs with T

– C pairs with G

• DNA replication is semi-conservative, meaning one original strand and one new strand.

original strand new strand

Two molecules of DNA

DNA REPLICATION - Two new molecules of DNA are formed, each with an original strand and a newly formed strand. Occurs in the NUCLEUS

• DNA contains the instructions to make proteins. RNA is a link between DNA and proteins.

replication

transcription

translation

• RNA differs from DNA in three major ways.

– DNA has a deoxyribose sugar, RNA has a ribose sugar.– RNA has uracil instead of thymine (found in DNA)

– A pairs with U– DNA is a double stranded molecule, RNA is single-stranded.

Transcription makes three types of RNA.

• Transcription copies a piece of DNA (a gene) to make a strand of RNA.

• Transcription copies a piece of DNA to make RNA• Transcription makes three types of RNA.

– Messenger RNA (mRNA) carries the message that will be translated to form a protein.

– Ribosomal RNA (rRNA) forms part of ribosomes where proteins are made.

– Transfer RNA (tRNA) brings amino acids (protein building blocks) from the cytoplasm to a ribosome to build the protein.

Amino acids (protein building blocks) are coded for by mRNA base sequences.

• A codon is a sequence of three nucleotides that codes for an amino acid.

codon formethionine (Met)

codon forleucine (Leu)

• Reading frame: multiple codons that code for a chain of amino acids• A change in the order in which codons are read changes the resulting

protein – this is why having a clear “start” and “stop” is important

• Common language: Regardless of the organism, codons code for the same amino acid.

Amino acids are linked to become a protein.

• An anticodon is carried by a tRNA. tRNA carries amino acids from cytoplasm to the ribosome.

EXAMPLE:mRNA codon=GUUtRNA anticodon=CTTAmino acid=Valine

What Are Mutations?

Changes in the nucleotide sequence of DNA

May occur in somatic cells (aren’t passed to offspring)

May occur in gametes (eggs & sperm) and be passed to offspring

Are Mutations Helpful or Harmful?

Mutations happen regularly Almost all mutations are neutral Many mutations are repaired by enzymes

Chromosome Mutations Five types exist:

Deletion – piece of chromosome lostInversion – piece of chromosome flips and

reattachesTranslocation – non-homologous

chromosomes trade piecesNondisjunction – failure of chromosomes to

separate during meiosis; leads to too many or too few chromosomes (i.e. Down Syndrome)

Duplication – piece of chromosome duplicated

Gene Mutations

• Change in the nucleotide sequence of a gene

• May only involve a single nucleotide

• May be due to copying errors, chemicals, viruses, etc.

Types of Gene MutationsInclude:

Point MutationsSubstitutionsInsertionsDeletionsInversionsFrameshift

Similar to the chromosomal versions of these mutations

Point Mutation

Change of a single nucleotideIncludes the deletion, insertion, or

substitution of ONE nucleotide in a gene

Nonsense Mutation• Type of point mutation (substitution)• Results in a premature stop codon

and usually a nonfunctional protein..may affect phenotype

Frameshift Mutation

Inserting or deleting one or more nucleotidesChanges the “reading frame” like changing a

sentenceProteins built incorrectly..may affect phenotypeOriginal:

The fat cat ate the wee rat.Frame Shift (“a” added):

The fat caa tet hew eer at.

Silent Mutations• Some mutations have no effect and are

called “silent” – type of substitution– Example:

• GUC changed toGUG

• Both code for theamino acidvaline

• This would not affect the proteinbeing made in any way, therefore would not affect phenotype.

Restriction maps show the lengths of DNA fragments.

• Gel electrophoresis is used to separate DNA fragments by size.– A DNA sample is cut with

restriction enzymes.– Electrical current pulls DNA

fragments through a gel.• Smaller fragments move faster

and travel farther than larger fragments.

• Fragments of different sizes appear as bands on the gel

DNA fingerprinting is used for identification.

• DNA fingerprinting is done using gel electrophoresis. It depends on the probability of a match.– Many people have the same number of repeats in a

certain region of DNA– The probability that two people share identical numbers of

repeats in several locations is very small – Several regions of DNA are used to make a DNA fingerprint

to make it more likely the fingerprint is unique.– Used in crime scenes, paternity tests, etc.– Compare banding patterns to make a match

Cloning

• A clone is a genetically identical copy of a gene or an organism

• Cloning occurs in nature– Bacteria (binary fission)– Some plants (from roots)– Some simple animals (budding, regeneration)

WHY CLONE???

• Making a genetically identical copy of something increases the chances the copy will have the same traits as the original.

Genetic Engineering• Involves changing an organism’s DNA to give it new traits• Based on the use of recombinant DNA

– Recombinant DNA contains DNA from more than one organism

(bacterial DNA)

Uses of Genetic Engineering• Transgenic bacteria can be used to produce

human proteins– Bacteria can be used to produce human insulin for diabetics

• Transgenic plants are common in agriculture– transgenic bacteria infect a plant– plant expresses foreign gene– many crops are now genetically modified

(GM)• Gives them traits like resistance to frost, diseases,

insects• Increase crop yield – more food quickly and cheaply

• Transgenic animals are used to study diseases and gene functions

Darwin observed differences among island species.

• Variation: difference in a physical trait of an individual compared to others in the same group– Galapagos tortoises, Galapagos finches

• Adaptation: feature that allows an organism to better survive in its environment– Species are able to adapt to

their environment– Adaptations can lead to

genetic change in a population

Several key insights led to Darwin’s idea for natural selection.

• Natural selection: mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals

• Heritability: ability of a trait to be passed down• There is a struggle for survival due to

overpopulation and limited resources• Darwin proposed that adaptations arose over

many generations

Biogeography• Island species most closely resemble

nearest mainland species• Populations can show variation from one

island to another• Example: rabbit fur vs. climate

Embryology

• Similar embryos, diverse organisms

• Identical larvae, diverse adult body forms

• Gill slits and “tails”as embryos

Larva

Adult barnacleAdult crab

Homologous Structures

• Similar in structure, different in function• Evidence of a common ancestor• Example: bones in the forelimbs of different

animals (humans, cat legs, whale fins, bat wings)

Vestigial Organs/Structures

• Remnants of organs or structures that had a function in an early ancestor but have lost their function over time

• Evidence of a common ancestor• Examples:

– Human appendix & tailbone– Wings on flightless birds (ostrich, penguins)– Hindlimbs on whales, snakes

Molecular Biology• Common genetic code (A, T, C, & G)• Similarities in DNA, proteins, genes,

& gene products• Two closely related organisms will

have similar DNA sequences & proteins

Genetic variation in a population increases the chance that some individuals will survive.

• Genetic variation leads to phenotypic variation– Necessary for natural selection

• Genetic variation is stored in a population’s gene pool– Made up of all the alleles in a population

• Allele combinations form when organisms have offspring

Directional Selection

• Favors phenotypes at one extreme

Stabilizing Selection

• Favors the intermediate phenotype

Disruptive Selection

• Favors both extreme phenotypes

Gene Flow• Movement of alleles between populations• Occurs when individuals

join new populations and reproduce

• Keeps neighboring populations similar

• Low gene flow increases the chance that two populations will evolve into different species

bald eagle migration

Genetic Drift• Change in allele frequencies due to chance• Causes a loss of genetic diversity• Common in small populations• Bottleneck Effect is genetic

drift after a bottleneck event– Occurs when an event

drastically reduces population size

• Founder Effect is genetic drift that occurs after the start of a new population– Occurs when a few individuals start a new

population– Decreases variation

Extinction

• Species go extinct because they lack the variation needed to adapt

Food Chains & Food Webs• Food chain: a model that shows a sequence of feeding relationships.

– Shows the transfer of energy from oneorganism to another– Each level of nourishmentin a food chain is called a trophic level*There is more energy at Lower levels in the foodchain

Preserving biodiversity is important to the future of the biosphere.

• Biodiversity: The variety of living things in an ecosystem

• The loss of biodiversity has long-term effects.– loss of medical and technological advances– extinction of species – loss of ecosystem stability (more biodiversity=more

likely an ecosystem can recover from disasters…implications for agriculture?)

Loss of habitat eliminates species.

• Habitat fragmentation prevents an organism from accessing its entire home range.– occurs when a barrier forms within the habitat– often caused by human development