Genetics Exam 1

Epigenesis

Proposed by William Harvey, stating that an organism develops from a fertilized egg through a series of development → differentiation

Preformation

The idea that a fertilized egg contains a complete miniature adult, called a homunculus.

Cell Theory

Proposes that all organisms are composed of cells, all existing cells arise from pre-existing cells, and a cell is the most basic unit of life.

Spontaneous Generation

The belief that living organisms could arise from nonliving matter, which was disproven by Louis Pasteur in 1859 (cell theory disproves)

Theory of Evolution

Developed by Charles Darwin, stating that species arise from ancestral species through descent with modification.

Natural Selection

A mechanism for evolutionary change where individuals with favorable traits are more likely to survive and reproduce.

Mendel's Laws

Includes the Law of Segregation and the Law of Independent Assortment, describing how alleles segregate during gamete formation.

Allele

Alternative forms of a gene that can produce different observable traits (phenotypes) in an organism.

Genotype

The set of alleles for a given trait carried by an organism.

Homologous Chromosomes

Pairs of chromosomes that contain the same genes but may have different alleles.

Mutation

Any heritable change in the DNA sequence that can lead to genetic variation.

Central Dogma of Molecular Biology

DNA→ Transcription → RNA→ Translation → Protein

Recombinant DNA (rDNA)

DNA that has been artificially created by combining sequences from different sources.

• Example: Put a gene in bacteria to study a protein in isolation

• Helps understand function, structure, and disease mechanisms

rDNA allows bacteria or other cells to make human proteins cheaply and safely - medicine (mass production of proteins)

• study proteins, knockout genes, make meds, GMOs, cloning, genetic testing

Model Organisms

Species that are widely used in genetic research due to their ease of care and genetic analysis.

Biotechnology

Technological applications that use biological systems or living organisms to develop or create products.

schleiden

plants

schwann (swan)

animals

disproving spontaneous generation (pastier)

Swan neck flask allows air but blocks the passage of
dust and microbes
• Flask 1: remained free of bacterial growth for years
• Flask 2: microbial growth present
• Flask 3: tilted on side so broth reached the bend in
swan neck, microbes grew immediately

natural selection

HOW evolution happens

the process where individuals with traits better suited to their environment survive and reproduce more, so those traits become more common over generations.

Theory of evolution

WHAT happens and WHY

the scientific theory explaining that populations change over time, share common ancestors, and diversify into new species. It includes multiple mechanisms, not just natural selection.

eukaryote

organisms whose cells contain a nucleus and membrane-bound organelles (living thing made of cells that have a nucleus)

mitosis

Daughter cells receive diploid (2n) set of
chromosomes identical to parent cell

meiosis

▪ Gamete formation (egg cells/sperm)
▪ Daughter cells receive one chromosome
from parent cell, resulting cell is haploid (n)

X

Gene = eye color

alleles = the version of the gene for eye color ( B or g)

• Mom’s allele: Brown (B)

• Dad’s allele: Green (g)

Genotype → the pair of alleles you inherit: one from mom, one from dad → what is actually in your genes

• Example: B g (Brown from mom, Green from dad)

Phenotype → what your body shows

Avery, MacLeod & McCarty

Dna is the carrier of genetic information in bacteria

Avery, MacLeod & McCarty EXPERIMENT

• S strain = smooth, disease-causing bacteria

• R strain = rough, harmless bacteria

They used these two strains to show that traits can be transferred between bacteria.

transformation

When a bacterial cell takes up foreign DNA and expresses the genes on it

• R strain bacteria = harmless, rough-looking bacteria

• S strain DNA = DNA from harmful smooth bacteria

• Transformation happens when R strain “picks up” DNA from S strain.

• After taking the DNA, the R strain starts showing the traits of S strain.

• In short: R strain “changes” because it absorbed S DNA.

What happened when R strain cells were mixed with S strain DNA

Only R strain cells transformed with S strain DNA expressed S strain traits

• They put harmless R bacteria together with DNA from harmful S bacteria.

• Only the R bacteria that actually took in the S DNA became harmful.

• This proves that DNA alone carries the information for traits — it’s not proteins or anything else.

Imagine R strain = blank recipe book and S DNA = a cookie recipe → After copying the recipe from S, R strain can now bake cookies (show S traits)

What did Hershey & Chase demonstrate in 1952?

DNA, not protein, is the genetic material in viruses.

used viruses (bacteriophages) to prove it’s DNA that carries genes.

hershey and chase

labeled protein using radioactive sulfer

• Proteins contain sulfur, DNA does not

• This allowed them to track protein in the virus

labeled DNA using radioactive phosphorus

• DNA contains phosphorus in its backbone, protein has very little

• This allowed them to track DNA in the virus

• Sulfur = in proteins, not DNA → tracks proteins

• Phosphorus = in DNA, not protein → tracks DNA

Only DNA enters the bacterial cell and controls new virus production → DNA is the carrier of genes.

Watson & Crick

first working model of DNA

Watson & Crick

They built the double helix model of DNA

A = T and G = C

nucleotide

subunit of DNA

Types of nitrogenous bases in DNA

Purines = A (adenine) & G (guanine) → double ring

Pyrimidines = T (thymine) & C (cytosine) → single ring

gene knockout

A tool that turns off a specific gene to see what happens

• Shows the role of that gene in an organism

• Common in research to understand diseases

organelles

Specialized structures (nucleus, mitochondria, ER) inside eukaryotic cells; absent in prokaryotes (bacteria)

eukaryotic

A cell that has a nucleus and internal compartments (organelles) → Humans

chromatin

DNA wrapped around proteins in the nucleus so it fits inside the nucleus during interphase

found in eukaryotic nuclei during interphase (DNA wrapped around histones)

DNA is not always tightly packed. When the cell isn’t dividing, DNA is loose and readable, that loose form is chromatin.

karyotype

A picture of all chromosomes in a cell, arranged by size.

nucleus

A membrane-bound organelle that houses linear genomic DNA (gDNA) (stores genetic instructions). has chromatin and nucleolus

Nucleolus

rRNA is synthesized and ribosome assembly begins.

Cytosol

Gel-like substance inside the cell

Cytoplasm

cytosol plus organelles and substructures

function of the rough ER

• protein synthesis

• Translation of mRNA into proteins via bound ribosomes

function of the smooth ER

• synthesizing fatty acids and
  phospholipids (lipid metabolism)

Free ribosomes

proteins used inside the cell (within cytosol)

Bound ribosomes

• proteins for secretions

• proteins for insertion into membranes

• proteins packaging within certain
  organelles

mitochondria/chloroplasts (plants)

• autonomous → contain their own DNA and ribosomes and can grow/divide independently.

centromere

sister chromatids are joined

• in various locations

• organize spindle fibers during mitosis and meiosis

arms of a chromosome

p arm → petite/short arm

q arm → long arm (next letter in alphabet)

homologous chromosomes

• Chromosomes completely
  compact and easily
  visualized during mitosis

• A maternal and paternal chromosome pair with the same gene loci (same genes location but potentially not same version)

karyotype

A visual representation of all chromosomes in a somatic cell arranged by size and shape

• members of same species
  contain an identical # of
  chromosomes

loci

Homologous chromosomes have identical gene sites but not necessarily the same allele

sister chromatids

• Identical copies of a chromosome formed during DNA replication

• After S phase, each chromosome is duplicated, but still counted as one chromosome

Sex chromosomes are not ___ in XY individuals

homologous (they differ in size and gene count)

Pseudoautosomal region

Present on both X and Y
chromosomes → allows pairing for meiosis

Haploid (n)

set of chromosomes collectively contains the genetic information of a genome

Diploid organisms

have 2 genomes

biparental inheritance

results in allels

Karyokinesis

Separation of DNA and Nucleus

• Requires replication of
  chromosomes into two nuclei (same size) that have chromosomes identical to the parent cell

Cytokinesis

division of the cytoplasm

• splits the volume into 2

• new cells with complete plasma membranes

• organelles replicate (1/2 size)

G1 phase

growth

S phase

dna replication (only happens once)

• Synthesis of new
  chromosomes to generate
  sister chromatids

G2 phase

• cell volume has doubled

• DNA has replicated

• preparing for mitosis

G0 phase

Not preparing for DNA replication or division

• non dividing state (most adult cells)

Prophase

over half of mitosis

Migration of 2 pairs of centrioles to
opposite ends of the cell, centromeres organize so spindle fibers form, nuclear envelope breaks down, chromatin (DNA+protein) condenses, chromosomes are visible

• dna goes from a string to chromosomes

Centrioles

establish poles at the end of the cell

centromeres

organize cytoplasmic microtubules into spindle fibers

cohesion

holds together sister chromatids

Prometaphase

Chromosome movement to the
plane

Metaphase plate

The center line where chromosomes align

Metaphase

Chromosome configuration at
the plane

Kinetochore

Protein structure on the centromere that spindle fibers attach to.

Cohesin

holds chromatids

Separase

degrades cohesion

Shugoshin

protects cohesion at centromere region

anaphase

Sister chromatids separate and move to opposite poles

disjunction

Shugoshin degraded, Cohesin cleaved by separase, Sister chromatids pulled towards the opposite poles

motor proteins

Molecular motors using ATP as energy and shorten spindle fibers

Telophase

reversal of prophase events and two complete sets of chromosomes are present

Cyclins

proteins that vary in their
concentration throughout the cell cycle

• 3 major checkpoints

Crossing over

Genetic exchange between
members of each homologous pair of
chromosomes

synapsis

Pairing of homologous chromosomes in prophase I for crossing over to happen

tetrads

Two homologous chromosomes (4 chromatids total)

• visible evidence of duplication

chiasma

Physical points where crossing over occurred.

• where the chromatids have intertwined

Nondisjunction

If an error occurs and
separation doesn’t happen properly

Reductional division meiosis 1 only

reduces number of
centromeres in half (disjunction)

Difference between meiosis I and meiosis II

• Meiosis I: homologous chromosomes separate (reduction)

• Meiosis II: sister chromatids separate (like mitosis)

Monohybrid cross

mating true-breeding individuals from 2 parent
strains

Genotype

Traits written in pairs to represent the two alleles

• Homozygous: DD, dd

• Heterozygous: Dd

Test Cross

Cross an organism expressing
the dominant phenotype
(unknown genotype) crossed
with a known homozygous
recessive individual