Download Homologous chromosomes

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, a
specific position on a pair of
homologous 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 segregate
during 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% Pink
Genotype 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)
B
B
W
W
BB
BW
BW
WW
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 males
25% Color Blind males
Genotype: 25% XBXb
(Carrier)
25% XbY
25% XBXB
25% XBY
Human Blood Types: Use both codominance 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 helix
DNA 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 nitrogen-containing
base
deoxyribose (sugar)
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
G
A
C
T
DNA REPLICATION - Two new molecules of DNA are formed, each with an original
strand and a newly formed strand. Occurs in the NUCLEUS
•
DNA replication is semi-conservative, meaning one original strand and
one new strand.
original strand
Two molecules of DNA
new strand
• 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 for
methionine (Met)
codon for
leucine (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=GUU
tRNA anticodon=CTT
Amino 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 lost
 Inversion – piece of chromosome flips and
reattaches
 Translocation – non-homologous chromosomes
trade pieces
 Nondisjunction – 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 Mutations
 Include:
Point Mutations
Substitutions
Insertions
Deletions
Inversions
Frameshift
Similar to the chromosomal versions
of these mutations
Point Mutation
 Change of a single nucleotide
 Includes 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 nucleotides
 Changes the “reading frame” like changing a
sentence
 Proteins built incorrectly..may affect
phenotype
 Original:
 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 to
GUG
• Both code for the
amino acid
valine
• This would not
affect the protein
being 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 crab
Adult barnacle
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 one
organism to another
– Each level of
nourishment
in a food chain is
called a trophic level
*There is more energy at
Lower levels in the food
chain
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