Gen Bio Unit II

Wild type

the most common phenotype found in natural populations 

Mutant phenotype

traits that differ from the wild type

Sex-linked genes

genes located on either sex chromosome

Heterogametic 

half of the sperm gets an X and the other half gets an Y (XY)

Homogametic

all eggs have X chromosome (XX)

Y chromosome

carries genes for male development

X - linked traits 

traits controlled by genes on the X chromosome 

Hemizygous

have just one allele for a gene (B) or (b)

Homozygous

have two identical alleles (BB) or (bb)

X - inactivation

one X chromosome inactivates to equalize gene dosage within a female

Barr body

inactivated X chromosome which modifies DNA methylation

Transformation 

a change in genotype or phenotype due to assimilation of external DNA 

Nucleotides

monomers of nucleic acids

3 parts of a nucleotide

1. Phosphate group (P)

2. Sugar (5 Carbon)

3. Nitrogen base (varies)

Purines

large 2-ring molecule

1. adenine

2. guanine

Pyrimidines 

small 1-ring molecule

1. Cytosine 

2. Thymine 

Double helix

2 strands of DNA wound around each other

Outside DNA strand 

sugar phosphate backbone 

Inside DNA strand

made of nitrogenous bases

How many bonds hold A & T strands together

2 hydrogen bonds 

How many bonds hold G & C strands together

3 hydrogen bonds

Antiparallel

causes strands to run in opposite directions

Semi-conservative replication

made up of a template strand and a new complementary strand

Origin of replication

starting site for replication initiation

DNA helicase

enzyme that unwinds the double helix

Primase

enzyme that creates primers

DNA Polymerase

enzyme that synthesizes new strands of DNA in the 5’ to 3’ direction

Phosphodiester bond

creates the sugar phosphate backbone

Ligase

enzyme that connects the lagging strands

Daughter cells

get a complete copy of the parent cells genome

Genome

a cells total genetic material

Chromosomes in prokaryotes

1 circular molecule of DNA

Chromosomes in eukaryotes

more than 1 linear molecule of DNA

Chromosome

molecule of DNA wrapped around proteins

Chromatin

identical half of a replicated chromosome

Haploid (n)

contain one complete set of chromosomes 

Diploid (2n)

contain two complete sets of chromosomes

Interphase

time between cell divisions 

G1 phase

grows and develops cell

Synthesis phase (S)

replicates the cells DNA & forms sister chromatids 

Sister chromatids 

identical copies of a single chromosome 

G2 phase 

prepares the cell for division 

Centromere

joins the sister chromatids together

Prophase

chromatids condense into chromosomes 

nuclear envelope breaks down 

miotic spindles form

Miotic spindles 

move chromosomes to the opposite ends of the cell 

Metaphase

chromosomes align at the middle of the cell

Anaphase

sister chromatids are pulled apart (diploid)

Telophase

new nuclei form around the chromosomes (diploid)

Cytokinesis

splits the cytoplasm

Result of Mitosis

two identical diploid cells

Cleavage furrow

region where parent cell pinches forward 

Prophase I

chromosomes match up with their homologous pairs and cross over

Crossing over

transfer of genetic information

Metaphase I

homologous pairs line up in the middle

Anaphase I

homologous chromosome pairs are pulled apart

Telophase I

new nuclei form around the homologous chromosomes

Prophase II

chromosomes condense (no crossing over)

Metaphase II 

chromosomes align in the middle in a single file line

Anaphase II

sister chromatids are pulled apart (haploid)

Telophase II 

new nuclei form around the chromosomes (haploid)

Result of Meiosis

4 non-identical haploid cells 

Gametes

reproductive cells that transmit genes from one generation to the next

Sexual reproduction

fusion of 2 gametes to form a zygote

Zygote

diploid cell resulting from fertilization

Costs of sexual reproduction

slow

high E requirement

dangerous

result in few offspring 

Advantages of sexual reproduction

genetic variation

Prokaryote gene regulation  

occurs at the transcription level (no nucleus) 

Lac Operon model organism

E. Coli

E. coli

adjusts its diet based on its hosts diet

Lac operon 

segment of DNA that controls the metabolism of lactose

3 components of lac operon

1. promoter

2. operator

3. sequence of 3 genes

Lac promoter

the binding site for RNA polymerase

Lac operator 

binding site for the lac repressor

Lac repressor 

protein that inhibits transcription

3 genes of the lac operon 

responsible for the digestion of lactose 

Negative regulation of the lac operon 

dependent on the presence or absence of lactose 

Inactive negative regulation

occurs when lactose is present 

allolacctose binds to the repressor → repressor cannot bind to the operator → RNA polymerase transcribes

Active negative regulation

occurs when lactose is absent → no allolactose 

repressor binds to the operator → RNA polymerase cannot transcribe

Allolactose

prevents the lac repressor from binding to the operator

Positive regulation of the lac operon 

determined by the presence or absence of glucose 

Inactive positive regulation 

occurs when glucose is present

the lac promoter has low affinity for RNA polymerase (low cAMP)

Active positive regulation

occurs when glucose is absent 

the lac promoter has high affinity for RNA polymerase (high cAMP)

CAP

increases the lac. promoters affinity for RNA polymerase

cAMP

hunger signaling molecule produced when glucose levels are low

Pre-mRNA modifications

1. alternative splicing

2. addition of a 5’ cap

3. addition of a 3’ poly-A tail

Alternative splicing

removes introns from pre mRNA strand

Significance of a poly-A tail

the length of a poly-A tail affects the level of translation

Long poly-A tail

mRNA breaks down slowly

Short poly-A tail

mRNA breaks down quickly

PCR

makes billions of copies of a specific DNA sequence

PCR Components 

1. Template DNA 

2. dNTPs

3. DNA primers

4. TAQ polymerase 

dNTPS

building blocks used by PCR to create a new strand

• A, T, G, C

TAQ Polymerase

heat resistant DNA polymerase

3 Steps of PCR 

1. Denaturation

2. Annealing 

3. DNA synthesis (extension)

Denaturration

heat separates the double helix and breaks the H-bonds

• ~ 90 degrees celsius

Annealing

adds primers to the newly synthesized strand

• ~ 40-65 degrees Celsius

DNA synthesis (extension)  

TAQ polymerase joins the strand at the 3’ end and continues to synthesis it

• ~ 72 degrees Celsius 

Gel electrophoresis

a technique used for separating molecules by size 

• confirm PCR results

Nitrogenous bases of RNA 

AU 
GC 

codons

a sequence of 3 nucleotides