Borgon Molec Bio lecture 1 & 2 objectives

What is Mendel's Law of Segregation?

Each organism has two alleles for each trait, which segregate during gamete formation, ensuring each gamete carries only one allele.

What is Mendel's Law of Independent Assortment?

Genes for different traits assort independently of one another in the formation of gametes, applicable when genes are on different chromosomes.

What did Mendel observe in his pea plant experiments?

He observed 3:1 phenotypic ratios in F2 generations, leading to conclusions about dominant and recessive traits.

Why were pea plants chosen for Mendel's experiments?

Pea plants were ideal due to distinct traits, controlled mating, and rapid growth cycles.

What are alleles?

Variants of a gene found at a specific locus on a chromosome.

What is the difference between homozygous and heterozygous?

Homozygous has two identical alleles for a trait (e.g., AA or aa), while heterozygous has two different alleles for a trait (e.g., Aa).

How do you perform a Punnett Square for a single trait?

Use a 2x2 grid for single trait outcomes.

What is the phenotypic ratio of a dihybrid cross?

The expected phenotypic ratio in F2 generations from a dihybrid cross is 9:3:3:1.

What is incomplete dominance?

A type of inheritance where traits are blended

Example of incomplete dominance

pink flowers from red and white parents

What defines codominance?

Both alleles are expressed fully in the phenotype

Example of codominance

AB blood types

Give an example of multiple alleles.

Blood type is controlled by multiple alleles, such as A, B, and O.

Define multiple alleles

More than two alleles control a trait

What is polygenic inheritance?

Traits that are controlled by multiple genes

Examples of polygenic inheritance

Skin color

What is epistasis?

One gene modifies the expression of another

Examples of epistasis

Coat color in dogs

What happens during mitosis?

Mitosis produces identical diploid cells, consisting of stages: prophase, metaphase, anaphase, and telophase.

What are the key differences between meiosis and mitosis?

Meiosis produces haploid gametes while mitosis produces diploid cells; meiosis involves two rounds of division.

What happens during metaphase in Mitosis?

Chromosomes align at the metaphase plate

What happens during anaphase in Mitosis?

Sister chromatids separate

What is the result of mitosis?

Two identical daughter cells (2n each)

What does Meiosis produce?

Haploid gametes (2n to n)

What is a requirement of meiosis?

crossing over

What is independent assortment in genetics?

The principle that genes on separate chromosomes assort independently during gamete formation.

How are linked genes inherited?

Linked genes show less frequent recombination and tend to be inherited together unless separated by crossing over.

Beadle and Tatum experiment

Studied mold mutants and developed the one gene- one enzyme hypothesis

Griffith experiment

Studied rough (R) and smooth (S) strains of bacteria to show transformation

Avery experiment

Digested DNA, RNA, Proteins, etc. to show that the transforming agent was DNA

Chargaff’s Rules

A=T, G=C. Disproved the tetranucleotide hypothesis

Hershey-Chase Experiment

Showed the DNA (32P) enters the host cell, not not protein (35S)

Franklins diffraction

X-ray data confirmed that DNA is helical and composed of 2 strands

Watson and Crick

Modeled the structure of the DNA double helix

Kornberg’s experiment

Showed that DNA replication was 5’ to 3’

Meselson-Stahl experiment

Showed DNA replication is semi-conservative

What is the significance of recombination frequency?

Recombination frequency indicates how often crossing over occurs between two genes and is used to calculate gene linkage.

How do sex-linked traits behave in inheritance?

Sex-linked traits are associated with sex chromosomes, such as X-linked conditions like color blindness.

What did McClintock's experiment demonstrate?

It demonstrated crossing over in corn using chromosomal markers and established linkage and crossover events.

What are two-factor and three-factor crosses used for?

To map genes and analyze gene order based on recombination frequencies.

How do you determine gene order using three-factor crosses?

By analyzing the phenotypes of offspring to identify the least frequent recombinants.

What is the connection between genetic markers and recombination frequency?

Genetic markers are used to map genes and calculate recombination frequencies, accounting for double crossovers.

What do genetic disorders linked to enzyme mutations illustrate?

They advance the understanding of metabolic pathways and genetic inheritance, such as alkaptonuria and phenylketonuria.

Genetic linkage occurs when genes are..?

located close together on the same chromosome

Linked genes tend to be inherited more/less frequently than genes on different chromosomes

More

Crossing over is the exchange of…?

genetic material between homologous chromosomes during meiosis

The frequency of crossing over between two genes is related to..?

Their physical distance on the chromosome

Genes that are closer together on a chromosome have a lower/higher chance of bering separated by crossing over

Lower

Linkage percentage ranges from..?

50% to 100%

Recombination percentage ranges from..?

0% to 50%

What is the benefit of using E. coli in genetic studies?

E. coli has a rapid generation time (~20 minutes) and a haploid genome, facilitating the observation of mutations.

What concept did the Beadle and Tatum experiment propose?

The one gene–one enzyme hypothesis, linking specific genes to specific enzymes.

What did Beedle and Tatum expose spores to?

X-rays to induce mutations, resulting in strains dependent on supplements

What happens when a mutation occurs in a sequential metabolic pathway?

A mutation can halt the pathway, leading to the accumulation of substrate.

How did biochemists categorize lipids and carbohydrates?

homopolymers or repetitive heteropolymers, can be built from single enzymes

How did biochemists categorize proteins?

polypeptide chains, non-repetitive heteropolymers

How did biochemists categorize nucleic acids?

polynucleotide chains

What is the Central Dogma of Biology?

The flow of genetic information is DNA → RNA → Protein.

How is the genetic code degenerate but not ambiguous?

Multiple codons encode the same amino acid and each codon specifies only one amino acid.

What is the significance of Vernon Ingram's studies on hemoglobin?

He identified that a single amino acid substitution (glutamate to valine) leads to sickle cell anemia.

What was the purpose of Griffith's experiment with Streptococcus pneumoniae?

To demonstrate the concept of transformation, showing that heat-killed virulent strains could transform non-virulent strains.

What did Avery’s experiment reveal about the transforming substance?

That DNA is the transforming substance responsible for genetic information transfer.

What did Chargaff's rule indicate regarding DNA base pairing?

A = T and G = C; it revealed the base composition's variability across species.

What was the outcome of the Hershey-Chase experiment?

It confirmed that DNA, not proteins, is the genetic material by showing DNA enters bacterial cells.

Identify DNA nucleosides

Deoxyadenosine, deoxyguanosine, deoxycytidine, and thymidine

Identify RNA nucleosides

Adenosine, guanosine, cytidine, and uridine

What do nucleosides consist of?

a nitrogenous base (purine or pyrimidine) bonded to a sugar molecule (ribose in RNA, deoxyribose in DNA).

What do nucleotides consist of?

Consist of a nitrogenous base, a sugar (ribose or deoxyribose), and one or more phosphate groups.

Identify DNA nucleotides

Deoxyadenosine triphosphate (dATP), deoxyguanosine triphosphate (dGTP), deoxycytidine triphosphate (dCTP), and thymidine triphosphate (dTTP).

Identify RNA nucleotides

Adenosine triphosphate (ATP), guanosine triphosphate (GTP), cytidine triphosphate (CTP), and uridine triphosphate (UTP).

How did Kornberg's experiment contribute to our understanding of DNA synthesis?

It isolated DNA polymerase I and demonstrated that DNA synthesis requires a template and occurs in the 5’ to 3’ direction.

What does the Meselson and Stahl experiment illustrate about DNA replication?

That DNA replication is semiconservative, with each daughter molecule containing one original and one new strand.

Helpful table for DNA/RNA bases and nucleosides/nucleotides

JUST A TABLE FOR REFERANCE

What are the structural differences between DNA and RNA?

DNA is double-stranded with deoxyribose sugar and thymine; RNA is single-stranded with ribose sugar and uracil.

Original strands remain together; new strands pair.

Conservative DNA replication model

Each daughter molecule has one original and one new strand.

Semiconservative

Strands are interspersed with old and new DNA.

Dispersive

The results for the DNA replication models sup[ported the semiconservative model using ..?

density gradient centrifugation

What is the role of tRNA in protein synthesis?

tRNA carries specific amino acids and matches codons on mRNA to its corresponding anticodons.

Explain the differences between RNA and DNA structures

DNA: Double-stranded, deoxyribose sugar, thymine.

RNA: Single-stranded, ribose sugar, uracil.

Explain the differences between RNA and DNA functions

DNA stores genetic information

RNA translates and carries it for protein synthesis.

What is the significance of aminoacyl tRNA synthetases?

They charge tRNA with the correct amino acids and ensure accuracy during protein synthesis.

What did Brenner, Jacob, and Meselson demonstrate about mRNA?

That mRNA is the intermediary between DNA and protein synthesis.

What did pulse-labeling experiments reveal about protein synthesis directionality?

That proteins are synthesized from the amino (N) terminus to the carboxyl (C) terminus.

Why did Crick hypothesize that there was an adapter molecule to synthesize proteins from RNA?

He thought that adapter RNA recognition might be due to H-bonding

Recall the initiation and termination processes of transcription

• Initiation: Promoter regions (-10 and -35 sequences) guide RNA polymerase binding.

• Termination: Rho-dependent (helicase action, rho catalyzes the disassociation of mRNA) or rho-independent (hairpin loops, interferes with transcription).