CHAPTERS 1, 2, 8

3 divisions of genetics

• Transmission genetics

• Molecular genetics

• Population genetics

Transmission genetics

How organisms give their genetic info to their offspring

Purpose of model organisms

Is very hard to study people due to variability; model organisms provide a more stable testing basis

6 model organisms

1. Fruit fly

2. E. coli (bacterium)

3. Nematode

4. Thale-cress plant

5. House mouse

6. Baker’s yeast

4 main characteristics useful for genetic analysis

• Short generation time (so can produce numerous offspring)

• Ability to carry out controlled genetic crosses (small, known genomes)

• Can be reared in a lab environment

• Have numerous genetic variants

Gene

Fundamental unit of heredity carried in DNA/RNAG

Genome

All genetic info in a cell

Mutation

Alteration ot the nucleotide sequence (heritable)

Heritable vs. non-heritable mutation

Reproductive germ cells carry heritable mutations, somatic cells carry non-heritable ones

Genes are the

Fundamental unit of heredity carried in DNA/RNA

Genetic info is transferred from

DNA to RNA to protein

Mutations are

Permanent changes in genetic info passed from cell to cell/parent to offspring

Many genetic traits are affected by

Multiple factors

All organisms are thought to have evolved from a

Common ancestor around 4 billion years ago

Evolution is

Genetic change within populations

Coding system for genetic information is the

Same in all living organisms

A genome is a

Complete set of genetic instructions for any organism

Four core components of RNA/DNA genetic material:

1. Contain complex information

2. Replicate faithfully

3. Encode the phenotype

4. Have the capacity to vary

Nature prefers…

Diversity over sameness

Allele

Different “versions” of the same gene

Genotype’s relation to phenotype

Genotype is the DNA/RNA instructions, phenotype is the expression

Phenotype

Observable properties of an individual resulting from both genetic and environmental factors

Character

Heritable feature that varies among individuals (ex. color)

Trait

What we see; each variant for a character (ex. purple petals)

Phenotype is directly relates to its

Genotype

Genetic info is carried in

DNA

Short DNA sequences are

Genes

DNA make up

Chromosomes

Humans have how many copies of each gene, and why

2 copies of each gene; produced by a fusion of 2 gametes (with 1 copy of each gene)

Diploid cell

Two copies of each chromosome; somatic cells

Haploid cells

One copy of each chromosome; germ cells (1n sperm + 1n egg)

Homologous chromsomes

“Same name,” pair of chromosomes containing the same genes

Number of chromosome pairs in humans

23; on a karyotype, sex is the 23rd

Autosomes

Look same, have corresponding/possibly different variations of genes

Sex chromosomes (pair of either XX or XY) are the

Basis for biological sex

Alleles

Alternate versions of the same gene with different nucleotide sequences; give rise to different traits

Mutations

Stable (unlikely to change/break), inherited changes in the genetic material that are not necessarily bad

Wild type

Allele present in most of the population (out in the “wild); other alleles are mutant alleles

Wild-type & mutant alleles reside at the same

Genetic locus

Locus

Specific position of an allele on a chromosome

What makes a gene polymorphic

If the wild-type allele is present <99% of the time

Prokaryote core principle

Unicellular, no membrane-bound complex

Prokaryotic cell reproduction occurs through; at a

Binary fission; high rate

Binary fission

Separation of replicated circular chromosome (simple division)

Viruses are not

Made up of cells; are neither prokaryotic or eukaryotic

Eukaryotes are both

Unicellular and multicellular

Eukaryotic genetic material is surrounded in a

Nuclear envelope to form a nucleus

DNA is closely associated with

Histones; used to form tightly-packed chromosomes

Mitochondria & chloroplasts divide

Separately from cells due to having their own genetic information

Nucleic acids

Polymers specialized for storage, transmission, & use of genetic information

Core difference between DNA and RNA

RNA has ribose, and DNA does not (deoxy)

3 components of nucleotides

1. Nitrogen-containing base

2. Pentose sugar

3. Phosphate group

Purines

2 fused rings; small name, but big structure

Pyrimidines

Have 1 ring; big name, little structure

DNA backbone formed through

Phosphodiester bonds (between nucleotides)

Phosphate groups link which carbons together

Link the 3’ carbon in 1 sugar to the 5’ carbon in the next sugar

Nucleic acids grow in which direction, and via what

5’ to 3’ direction via condensation reactions

What hold DNA strands together

Hydrogen bonds between purines and pyrimidines

Complementary base pairs (and #s)

• Adenine & thymine (2 bonds)

• Guanine & cytosine (3 bonds)

How DNA ALWAYS runs

Antiparallel (two different directions)

Major and minor grooves make up

3D structure of DNA (as per Watson & Crick)

Minor groove distancing vs. major groove

Backbones are closer together on one side (minor) than the other (major)

Where does hydrogen bonding happen

Outer edges of the base pairs

Key to protein-DNA interactions

Binding of proteins to specific base pair sequences

Meaning of “right-handed” in DNA organization

Twists and turns as we go upwards

3 different secondary structures

1. A form

2. B form

3. Z form

B form of DNA is special because it is

The most common, stable form of DNA

Supercoiling

DNA is overwound & underwound, causing it to twist on itself

Positive vs. negative supercoiling

• Positive: overrotated (overwound)

• Negative: underrotated (underwound)

Topoisomerase

Enzymes responsible for unknotting/unwinding DNA during transcription/translation

Positive or negative, which is more common

Negative; allows better access to the DNA for replication and translation than a neutral cell

• Easiest for cell’s machinery to access info

What forms the structure of chromatin

Nucleosomes

Histone protein function

“Pack” and organize DNA molecules

Role of amino acids in histone proteins

Have a positive charge that attract the negative phosphate groups of DNA

• Will stick to each other

Linker DNA

a high-order chromatin structure that can become more compressed when you add methyl groups (methylation)

Width of eukaryotic chromosomes

250 nm wide

4 types of histone proteins, and their quantity

• HB2A

• HB2B

• HB3

• HB4

2 of each type on chromatin, 8 total

Role of histone h1

Helps hold DNA onto the histone “core”

Epigenetic changes

capable of being reversed, and often due to environmental factors

Example of epigenetic change

Methylation; if this change occurs in LARGE amounts, then can cause a change in expression

Euchromatin vs. heterochromatin

Loosely packed form of DNA that is often active in transcription, while heterochromatin is often tightly packed and inactive

Staining in euchromatin vs. heterochromatin

Light; dark

Location for euchromatin vs. heterochromatin

On chromosome arms; at centromeres, telomeres, & other specific places

Type of sequences in euchromatin vs. heterochromatin

Unique; repeated

Presence of genes in euchromatin vs. heterochromatin

Many; few

Time of replication for euchromatin vs. heterochromatin

Throughout S phase; late S phase

Transcription frequency in euchromatin vs. heterochromatin

Often; infrequent

Crossing over frequency in euchromatin vs. heterochromatin

Common; uncommon

Barr body

Early in development, one X chromosome in human females is inactivated; in mammals it is heterochromatin

Selection of which X chromosome is silenced in females is

Random in each cell

3 main components of chromosome structure

• Centromere

• Telomere

• Origins of replication

Centromere

Constricted region of chromosome & attachment point for spindle microtubules

Telomeres

Tips of a linear chromosome; provide a means to replicate the ends of linear chromosomes

Origins of replication

Where the DNA synthesis begins; are thousands of locations all along the chromosomes where this happens

DNA sequence at the end of chromosome is very

Specific; will get chopped off every time a new cell gets made

3 components of the cell cycle

• Interphase

• M phase

• Phase checkpoints

Interphase

DNA synthesis, chromosome replication phase; extended period between cell divisions

M phase

Mitotic phase; separation of sister chromatids

Phase checkpoints

Key transition points where things that are starting to lose function are often altered

4 parts of interphase

• G₀

• G₁

• S

• G₂