Exam 3 Flashcards
Pangenesis Hypothesis
Inheritance by means of each organ sending information to the gametes. - Explains why children resemble their parents (not true)
Blending Hypothesis
averaged between parents (not true)
Natural Selection
More offspring produced than will survive.
Individuals with favorable traits will survive.
Traits are inherited from parents to offspring.
What happens when varieties with opposing traits are mated (monohybrid cross)?
One trait is completely lost in the first generation.
The missing trait returns in the second generation with 25% of the offspring/
Homozygous vs Heterozygous
Homozygous - PP or pp
Heterozygous - Pp
What happens when two traits are followed simultaneously (dihybrid cross)?
Dependent vs independent assortment.
Independent - 4 kinds of gametes from each plant, 16 possible genotypes with 4 phenotypes in f2 generation (9:3:3:1)
Dependent - if 1 trait depends on another, dihybrid crosses should resemble monohybrid crosses (3:1 ratio)
Independent Assortment - By chance, any two alleles for two different genes should only be inherited together in 50% of the offspring. This is not true for genes that are on the same chromosome, without homologous recombination, they should be inherited 100 percent of the time.
Independent Segregation
(monohybrid vs dihybrid)
Monohybrid Crosses - The two alleles for a trait segregate equally in gametes.
Dihybrid Crosses - Alleles for different traits assort independently (not always correct).
What are Mendel’s “factors”?
Alleles on chromosomes.
Meiosis explains inheritance patterns.
Most traits in plants and animals do not follow simple mendelian inheritance patterns, because most traits are governed by multiple alleles of multiple genes.
Mendel’s laws still apply to each individual gene (allele pair).
Are recessive alleles ever nonfunctioning alleles.
Yes, in many cases (not all).
Do any human traits follow Mendel’s observations?
Yes, only ones that are encoded by a single (dominant/recessive) gene.
Are any heritable disorders carried by a single allele.
Yes.
Sickle cell anemia, cystic fibrosis - single recessive allele.
Sickle cell allele selection hypothesis:
Sickle cell anemia provides some protection against malaria and may have been selected for in population that are exposed to malaria.
Give the family history of a trait, can the genotype of individuals be determined?
Yes
What are quantitative/continuous traits?
Continuous or quantitative traits are characteristics that demonstrate a wide range of phenotypes and are usually influenced by multiple genes, often in combination with environmental factors. These traits can take on a spectrum of values rather than distinct, categorical outcomes.
What can quantitative traits result from?
- Incomplete dominance or co-dominance of alleles.
- More than two alleles are present in a population.
- Multiple genes (with multiple alleles) contribute to the trait.
- Genes can interact with the environment.
Co-dominant alleles
Both effect the phenotype and may appear to blend in heterozygotes.
Incomplete dominance
Occurs when two copies of an allele are needed for one phenotype and a single copy gives a different phenotype.
Can blending occur?
Yes, when alleles are co-dominant or incompletely dominant. (Mechanism 1)
If there are more than 2 alleles for a given gene, does this mean that there can be more variations on a trait?
Yes (Mechanism 2)
Polygenic traits
Influenced by multiple genes.
Most traits in animals and plants. (Mechanism 3)
If enough genes influence a trait it will be considered continuous or quantitative rather than either or because there are intermediates between extremes.
Multifactorial traits
Traits that have a genetic basis but also respond to the environment.
What is a gene?
Something that codes for a protein
Diprosopia and Cyclopia
Diprosopia - Born with two faces.
Cyclopia - Born with one eye.
What causes Diprosopia and Cyclopia?
Too much or too little SHH expression in the midline leads to holoprosencephaly conditions. Too little or too much causes not enough or too much division.
What is Holoprosencephaly and how can it be explained?
Diprosopia and Cyclopia.
Can be explained by variation in SHH expression (resulting from mutations or environmental conditions that alter its expression).
White eye experiment in flies
White eyes gene resides on the X chromosome.
Half of the males expressed this trait and half didn’t.
Females inherit 2 X chromosomes and are therefore heterozygous for X chromosome alleles in F2 generation.
A higher percent of males will express the white eye gene because they either express it or they dont, over females who are heterozygous for the gene. But more females will be carriers of it than males.
Should we be able to map the location of a gene on a chromosome?
Yes.
If alleles for separate genes could be identified, their position on a chromosome could be determined based on their pattern of inheritance.
Independent Assortment - By chance, any two alleles for two different genes should only be inherited together in 50% of the offspring. This is not true for genes that are on the same chromosome, without homologous recombination, they should be inherited 100 percent of the time.
Due to homologous recombination, the farther apart two genes are on a chromosome the more likely it is that a cross over event will occur between them and recombine them.
Alleles from genes that are close together should be inherited together more often than genes that are farther apart on the same chromosome.
What are needed to map genes onto chromosomes?
Mendelian inheritance (purple and white flower expression, 3:1 ratio) and homologous recombination (meiosis).
b recombines with cn 9% of the time, with g 17% of the time, and cn recomines with g 9.5 percent of the time. What does this tell us about how far they are apart from each other on a chromosome.
Tells us that cn is in the middle, and b and g are on each side of cn.
How were morgan and students able to map hundreds of traits on chromosomes?
By determining how frequently traits assort independently.
How many pairs of chromosomes do fruit flies have?
4 pairs, 8 chromosomes.
What part of a chromosome carries genetic information?
Chromosomes are made of DNA and protein, either could potentially carry genetic information.
What transforms bacteria from nonpathogenic to pathogenic?
DNA, and only DNA.
Nonpathogenic vs pathogenic bacteria
Nonpathogenic - Not dangerous often beneficial existing naturally.
Pathogenic - Often can cause danger or disease to the host organism.
DNA is the genetic material of the T2 bacteria phage
DNA (not protein) is the genetic material of the bacteria phage T2 (bacteria virus).
What is DNA and how does it work?
4 Subunits (A, C, G, T), has a sugar, phosphate group, nitrogenous base. Total amount of A=T, C=G.
What is DNA composed of
Two helices that are complimentary and run anti-parallel to each other.
5’———3’
3’———5’
Why dont base pairs pair with anything outside of their complimentary pair?
Molecular Structure
A-T/U -> Two hydrogen bonds
C-G -> 3 hydrogen bonds
Complimentary DNA suggests how it could replicate.
The two chains unwind and separate.
Each old strand is a template for the addition of bases according to the base pairing rules.
The result is two DNA helices that are exact copies of the parental DNA molecule with one old strand and one new strand.
DNA replication is ____ ___________.
Semiconservative
This was figured out by growing many generations of bacteria with heavy isotope N15 rather than N14.
If DNA replication were conservative, the resulting DNA molecules would have been entirely heavy (15N-15N or old-old) or entirely light (14N-14N or new-new). However, the experimental results showed an intermediate hybrid pattern (15N-14N or old-new), supporting the semi-conservative model proposed by Watson and Crick.
Why is conservative wrong
Cant form a new DNA copy out of thin air, need a strand. De NOVO (making something new completely separate)
RNA is made De NOVO
Replicating off DNA and can exist by itself
DNA has to be made with another DNA.
RNA polymerase - De NOVO
DNA polymerase - not De NOVO.
Both strands of a double helix are used as ____
templates in DNA synthesis
DNA separates at the site known as…
Origin of replication.
DNA polymerase
Synthesizes new strand of DNA. Only synthesized in the 5’ to 3’ direction.
What adds nucleotides to a strand of DNA
DNA polymerase
DNA VS RNA Polymerase
Enzyme primase builds a short RNA primer to start the complimentary strand. Primase can add nucleotides de novo, DNA polymerase cannot.
DNA polymerase can add DNA nucleotides to the 5’ end of the RNA primer.
Leading vs Lagging strand
RNA and DNA polymerase only builds in 5’ to 3’ direction
Okasaki fragments - lagging strands of the DNA is being replicated - behind where the DNA polymerase starts.
DNA splitting
After DNA splits
RNA primase enzyme builds RNA primer prior to DNA polymerase.
RNA doesnt need primer and primase enzyme.
Replication Fork
Opening in DNA where replication starts.
DNA
Parental strands separate.
RNA primer is added.
DNA polymerase adds nucleotides to a growing new strand in the 5’ to 3’ direction.
The resulting daughter molecules have one old strand and one new strand.
The central dogma of genetic information:
DNA encodes genes, which are transcribed into mRNA and then translated into protein.
How many amino acids need to be specified?
20 amino acids, but only 4 nucleotides in DNA.
How many nucleotides make a codon, which codes for a single amino acid.
3 nucleotides, A sequence of DNA is copied to make a complimentary mRNA
At a ribosome, what is translated into a sequence of amino acids.
Codons
How is DNA turned into RNA
flipped from 5’—-3’ to 3’—-5’, then A’s turn to Us, Ts turn to As, and Cs and Gs are turned into each other.
Is genetic code (DNA) universal?
Yes mostly, 20 amino acids are used across almost all organisms.
The central dogma of genetic information (steps):
DNA encodes genes, which are transcribed into mRNA and then translated into protein.
When does gene expression begin?
when a mRNA is transcribed
Transcription
Copying a sequence of DNA into a mRNA
Translation
Using the mRNA sequence to order amino acids (via a ribosome)
How many nucleotides are needed to code for each amino acid?
At least 3 nucleotides are needed.
4*1 = 4 < 20
4 * 4 = 16 < 20
4 * 4 * 4 = 64 > 20
3 nucleotides make a _____, which codes for a single amino acid
codon
At a ribosome, codons are …
translated into a sequence of amino acids.
A sequence of DNA is copied to make a complimentary ____.
mRNA
Explain some evidence of translation.
When genetic code was elucidated when people learned to synthesize specific sequences of RNA and perform translation in test tubes.
Combined ribosomes and amino acids, could produce a protein.
Could then sequence the protein to figure out which amino acids were in it.
If you could copy a gene sequence from a bear and put that gene into a fly, would the fly make the same protein that the bear does?
Theoretically, yes.
Transcription is the…
directed, localized synthesis of RNA from a DNA template.
What enzyme carries out transcription?
RNA polymerase
RNA polymerase is recruited to a gene by a….
promoter sequence upstream of the coding portion of a gene.
RNA synthesis
Similar to DNA polymerase, except usig RNA nucleotides.
Only a small number of complimentary DNA nucleotides are separated at a time.
The mRNA is detached from the template strand, allowing DNA to re-anneal after synthesis.
Can synthesize “de novo”
Regulatory elements
Sequences of DNA that help to recruit and regulate RNA polymerase.
Transcription factors
Proteins that regulate gene expression, often by inhibiting or assisting RNA polymerase recruitment.
Introns vs exons
Introns - Eukaryote genes and some archaea have interrupting sequences called introns.
Exons - Protein coding regions
Intron and exon splicing
Introns are spliced out of the initial transcript inside the nucleus generating a mature transcript. The exons are spliced together to make a mature mRNA.
What does GTP do?
Modify nucleotides to make a 5’ cap.
Poly-A-Tail
An enzyme adds many adenines to the 3’ end of the transcript which makes a poly-a-tail.
What are the 5’ cap and poly-A-tail used for?
To transport the transcript out of the nucleus and are used by ribosomes to identify start codons.
RNA polymerase vs DNA polymerase
RNA polymerase:
unwind, single stranded, de novo.
DNA polymerase: double stranded, not de novo
Both: 5’-3’, require a template, p and oh (phosphate and hydroxyl group)
What does transcription need a ribosome to do?
Build a specific protein sequence based on the codons in mRNA.
How do ribosomes translate from RNA to amino acids?
tRNA
tRNA
have a complimentary anticodon and carry a specific amino acid matched to their anticodon.
Each tRNA has a specific…
enzyme that charges it with the correct amino acid.
What enzyme charges tRNAs? How many sites does this enzyme have?
Aminoacyl-tRNA synthetase.
2 sites.
What catalyzes the polymerization of amino acids?
Ribosomes
How are ribosomes assembled?
They’re assembled on mRNA.
The small subunit binds to mRNA, and exposes the start codon.
The tRNA specific to the start codon binds the mRNA, which then recruits the large subunit. There are also specific stop codons that disrupt ribosomes.
The large subunit contains the sites that interact with tRNA’s, and catalyzes the polymerization of amino acids.
Summary of major molecular events of the central dogma:
RNA polymerase is loaded onto a gene via promoters and transcription factors.
In eukaryotes, the initial transcript is spliced and modified before exiting the nucleus as a mature mRNA.
A ribosome assembles on the mRNA.
Charged tRNAs are used by the ribosomes to construct a peptide sequence based on the mRNA sequence.
Start and stop codons in DNA/mRNA are used to instruct the ribosome to build the correct protein.
DNA polymerase - how does it happen?
Catalyzes specifically to the phosphate end (5’) of a new nucleotide to the OH group (3’) of an existing DNA strand.
How does DNA synthesis get powered?
Incoming nucleotides have 3 phosphate groups, two are broken apart to release enough energy to power DNA synthesis.
What makes one cell different from another?
Almost every cell made by mitosis contains the exact same DNA.
Cells differentiate into nervous cells, bone cells, muscle cells… etc.
Differences between cells result from what genes they express.
How do we know every cell has the same DNA?
Cloning or asexual reproduction in vertebrates demonstrates that the entire genome is maintained in differentiating cells.
Dolly the sheep - first successfully cloned mammal.
Cloning has also been used to revive extinct species.
Can genes be regulated by other genes?
Yes, the Lac operon.
E.coli uses glucose for ATP production when high in abundance, when low in abundance it uses other sugars like lactose.
The proteins dedicated to metabolizing specific sugars varies based on availability.
Bacteria often regulate several genes that are part of the same …..
pathway using the same promoter.
Permease and transacetylase
Permease - Assists in moving lactose into a cell.
Transacetylase - Removes a toxic waste product.
What usually happens when something is absent to activate proteins.
A repressor protein blocks it.
The lac operon is highly expressed when lactose is available, and glucose is not.
The promoter for the lac operon is weak and is weakly expressed when glucose is present, even when lactose is present. The less glucose there is the stronger it is expressed.
The CAP protein binds the lac promoter strongly and can recruit RNA polymerase increasing lac operon expression.
CAP is activated by cAMP whihc is present when glucose levels are low.
Can Eukaryotes regulate gene expression at every stage of expression?
Yes.
Both eukaryotes and prokaryotes do the majority of their gene regulation at the transcriptional level.
Eukaryotes routinely regulate every step of gene expression.
Eukaryotes can regulate gene expression by regulating what parts of a chromosome are accessible to be expressed.
How do eukaryotes regulate gene expression after transcription?
Using small interfering RNA and microRNAs.
Does regulation of transcription follow the same principles as the lac operon?
Yes, transcription factors activate or inhibit transcription.
