Genetics Chapters 1-4 (Exam 1)

Genetics is…

the study of heredity and how inherited variation is:

- encoded (Packaged/stored), replicated (copied), expressed (used by an organism)

-how it evolves over time

The root of genetics: Gene comes from

Greek root: Origin, beginning, birth

Importance of Genetics

Development (How traits develop and are regulated)

Maladies (the causes and inheritance of diseases and disorders)

Agriculture (Genetically modified organisms)

Biotechnology (Vaccines, antibiotics, gene therapies)

Genome

A complete set of genetic instructions for any organism

Norman Borlaug

used breeding principles to develop wheat varieties that were:

-Drought-resistant

-Disease-resistant

-Frost-resistant

His work contributed to the Green Revolution which greatly increased food production worldwide

Biotechnology

uses living systems or biological materials to create useful products and technologies

(vaccines, antibiotics, anticancer treatment, gene-editing tools)

Unifying Principle: All organisms use genetic systems

Organisms use common information-storage and information-processing systems (particularly DNA and RNA)

• Because of shares genetic organization, discoveries in one organism can often provide insight into another

- Genetic principles studied in:

• Fruit flies

• Bacteria

• Plants

• Mice

• Humans

• Malaria-causing organisms

Within Cells Genetic Information is located in:

• Nucleus- eukaryotic

• Mitochondria- eukaryotic

• Chloroplasts- plants

• Cytoplasm- prokaryotes (lack nucleus)

Nucleic Acid

A polymer made of nucleotides

Two major nucleic acids:

• DNA (deoxyribose, sugar lacking a hydroxyl group at the 2’ carbon)

• RNA (ribose, hydroxyl groups at both the 2’ and 3’ carbons)

Nucleotide

The basic repeating unit (monomer) of DNA and RNA

It contains:

1. A sugar

2. A phosphate group

3. A nitrogenous base

Nucleoside

Contains:

1. A sugar

2. A nitrogenous base

Lacks the phosphate group found in nucleoTIDE.

Nitrogenous Bases

Contain nitrogen and have BASIC chemical properties:

DNA BASES:

• Adenine (A)

• Thymine (T)

• Guanine (G)

• Cytosine (C)

RNA BASES:

• Adenine (A)

• Uracil (U)

• Guanine (G)

• Cytosine (C)

Hydrogen Bonding:

• A—T or A—U pairs form TWO hydrogen bonds

• C—G pairs form THREE hydrogen bonds (require more energy to separate)

DNA and RNA Structure

• DNA strands are antiparallel, they run in opposite directions

• DNA generally forms a double-stranded helix.

• RNA can fold and pair with itself

Transmission Genetics (Classical/Mendelian)

Examines how traits pass from parents to offspring across generations

Focuses on: -

• Individuals

• Parents

• Offspring

• Genotypes and phenotypes

Ex: tracking inheritance of sickle cell alleles through family generations

Molecular Genetics

Examines the chemical and molecular nature of genes

Including:

• How information is encoded

• How DNA is copied

• How genes are expressed

• Gene structure and organization

• DNA or amino acid sequences

• Mutations that alter proteins

Ex: Sickle cell disease results from a mutation affecting the sequence of the hemoglobin protein

Population Genetics

Examines:

• Genetic composition of groups of individuals within the same species

• Distribution and frequency of alleles (How genetic composition changes over time)

• Evolution

Ex:

• Sickle cell allele frequencies are relatively high in regions of Africa, Asia, and India where malaria is common

• Carrying one sickle cell allele can provide some protection against malaria

• This shows how environmental conditions influence allele frequencies through natural selection

Model Organisms

• short generation times

• many offspring

• easily controlled laboratory conditions

• observable traits

• genetic variation

• practical laboratory maintenance

EX: Fruit flies, Bacteria, Roundworms, Plants, Mice, Yeast, Zebrafish

Pangenesis (Before DNA known)

Charles Darwin

• Each part of the body contains genetic information for that particular part

• Specific particles=gemmules carry info from parts of the body to reproductive organs

• Info passed to the embryo at the moment of conception

Inheritance of Acquired Characteristics

Jean-Baptist Lamarck

• Traits acquired in person’s lifetime become incorporation into that person’s hereditary information

• Traits passed on to offspring

This theory is incorrect with the exception of Epigenetics

Preformation

Inside egg or sperm exists a fully formed miniature adult (Homunculus)

Blending Inheritance

• Traits of offspring are a blend, or mixture of parental traits

• After “blending” the individual traits are not recovered in future generations

Cell Theory

Schleiden, Schwann, Virchow

• All life is composed of cells

• Cells are the fundamental unit of structure and function in living organisms

• Cells arise only from pre-existing cells

Evolution

Darwin, Wallace

• Put forth theory of evolution through natural selection

• Randomly acquired changes resulted in unequal reproductive success

Principles of Heredity

Gregor Mendel

• father of genetics

• laid foundation for our modern understanding of heredity

• Pea plants

• Monk

Chromosomes (history)

walter flemming

• observed division of chromosomes

• described mitosis

Germ-Plasm Theory

August Weismann

• Cells in reproductive organs carry a complete set of genetic info that is passed to egg and sperm

• mice tail cut experiment

Current Theories of genetics

• Genes are located on chromosomes

• Molecular structure of DNA

• DNA sequencing

• PCR (Polymerized Chain Reactions, How cells replicate)

• CRISPR-Cas 9 (sickle cell cure)

Prokaryotes Vs Eukaryotes: Prokaryotes

Nucleus: Lacks a nucleus

Cell Diameter: Relatively small (1-10 micro meters)

Genome: Single, Circular

DNA (packaging): Not highly ordered and in packed arrangement (No nucleus to hold it) No nuclear membrane or histone proteins (except in some Archaea)

Amt of DNA: Relatively Small

Membrane-Bound Organelles: Lack mem-bound Organelles

Uni or Multi-cellular: Unicellular

BOTH HAVE: Cellular membranes, ribosomes (site of protein synthesis)

Prokaryotes Vs Eukaryotes: Eukaryotes

Nucleus: Have a Nucleus

Cell Diameter: Relatively large (10-100 micrometers)

Genome: Linear, multiple

DNA (packaging): DNA is closely associated with histones to form tightly packed chromosomes

Amt of DNA: Relatively large

Membrane-Bound Organelles: Has mem-bound organelles

Uni or Multi-cellular: Multicellular

BOTH HAVE: Cellular membranes, ribosomes (site of protein synthesis)

Viral Cells

• Nonliving

• Outer protein coat

• Made up of one nucleic acid not both (DNA or RNA)

• Uses host cell to replicate (obligate)

• Intracellular parasite

Ex: Adenovirus is responsible for the common cold

Eukaryotic DNA

All humans have 23 PAIRS of chromosomes

A diploid (2n) organism has two sets of chromosomes organized as Homologous Pairs. (Aa, AA, aa)

Chromosomes

• Condensed “packaged” nucleic acids (Protein and genetic info—>Chromatin)

Chromatid

• ½ of duplicated chromosome

• If an “X” shape is made, sister chromatids are present, already gone through a copying stage

Chromatin

• Loose DNA + Histone proteins

Types of positioning of the centromere

Submetacentric

Metacentric

Telocentric

Acrocentric

Prokaryotic Cell Reproduction

Binary Fission:

1. DNA Replication

2. Copy Separation

3. Division of Cytoplasm

1 cell produce 71 billion cells in 10 hrs

• Copying starts at origin of replication in mother cell

• Contains a single circular chromosome made up of double-stranded DNA

• AS the chromosome replicates, the origins segregate to opposite sides

• SMC (Structural Maintenance Chromosome Proteins) help split cell

• Cell divides and has an identical copy of the original chromosome

Eukaryotic Cell Reproduction (Cell Cycle)

1. DNA Replication

2. Copy Separation

3. Division of cytoplasm

• More chromosomes, more complex, multiple origins in 1 chromo

• chromosome separated from cytoplasm by nucleus

• nuclear matrix is highly organized with internal scaffolding (must be broken down for cell division)

Cell Cycle: Interphase (general)

• consists of: G0, G1, G1/S check, S, G2, G2/M check

• 95% of cells time is spent in this phase

Cell Cycle: G1; Gap 1

• protons and organelles necessary for cell division synthesized

• Cell Grows

• Approx 10 hrs

Cell Cycle: G1/S Checkpoint

Cell commits to DNA Replications

Cell enters S phase

Cell Cycle: S Phase

• checks for errors

• quality control and damage repair

• DNA replicated/copied

• 9 hrs approx

Cell Cycle: G2; Gap 2

• Biochemical preparation for cell division (Microtubules assemble)

• 4 hrs approx

Cell Cycle: G2/M Check point

• commits to mitosis

• enters M phase

Mitosis

The division of the nucleus:

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

and cytokinesis following telophase

Mitosis: Prophase

• chromatin condenses into visible chromosomes

• mitotic spindle begins to form

• centrosomes move toward opposite sides of the cell

• Nuclear envelope breaks down

• Kinetochores form at the centromeres

• spindle microtubules gain access to the chromosomes

Types of Spindle Microtubules

Astral Microtubules- Extend outward from the centrosomes, help position the spindle apparatus within the cell

Polar Microtubules- Extend toward the opposite pole, interact with polar microtubules from other centrosome, push spindle poles away from one another, help position spindle

Kinetochore Microtubules- Attach to Kinetochores, move and eventually separate chromosomes during mitosis

Mitosis: Metaphase

• chromosomes align at the center of cell (metaphase plate)

• each sister chromatid should be attached to microtubules from opposite spindle poles

• produces balanced, HIGH TENSION across chromosome

Cell pauses at Spindle Assembly Checkpoint

Mitosis: Anaphase

• The centromeres split

• sister chromatids separate and move toward opposite spindle poles

• once separated, each chromatid is considered an individual chromosome

Mitosis: Telophase

• chromosomes arrive at opposite spindle poles

• new nuclear envelope begins forming around each chromosome set

• chromosomes decondense and return to relaxed chromatin state

• the nucleus has divided

Cytokinesis

Divides the cytoplasm after nuclear division (contractile ring made of actin filaments creates cleavage furrow)

result: 2 daughter cells genetically identical to each other and the parent

Chromosome and DNA molecule counting (Mitosis and cell cycle)

Before S phase:

• Chromosomes- 4

• DNA molecules- 4

AFTER S phase:

• Chromosomes- 4 (sister chromatids remain joined at their centromeres)

• DNA molecules- 8

During Anaphase:

• Chromosomes- 8 (sister chromatids are now separate and are now individual chromosomes)

• DNA molecules- 8

After Telophase and Cytokinesis:

• each daughter cell contains:

• —4 chromosomes

• —4 DNA molecules

KEY distinction: A duplicated chromosome contains 2 sister chromatids but is counted as 1 chromosome until the sister chromatids separate

DNA molecule count corresponds more closely to the number of chromatids

Mitosis Conclusion:

• PURPOSE: To repair and generate new body cells; produces genetically identical daughter cells

• OUTCOME: One diploid cell divides once to produce two diploid daughter cells

• Chromosome #: Remains constant— if starting with 2n, both daughter cells will have 2n chromosomes

• Ploidy status: The cell is NEVER haploid during mitosis

Meiosis and Sexual Reproduction (Conclusion):

• Purpose: To create haploid gametes (Sperm, egg) for sexual reproduction

• Process: Reduction Division; converts one diploid cell (2n) into four haploid cells (n)

• Division events: Two events (Meiosis I and Meiosis II)

• Genetic Benefit: Produces genetic variation through crossing over and independent assortment

• INTERPHASE PRECEDES BOTH DIVISIONS

Interkinesis

A brief gap between meiosis I and meiosis II

• NOTE: some cell types do NOT fully decondense chromosomes or reform nuclei during interkinesis; they proceed directly into meiosis II

• Most germ cells producing egg and sperm DO go through interkinesis

Meiosis I: Reduction division: Prophase I

• Where crossing over occurs

• Five substages (1. Leptotene 2. Zygotene 3. Pachytene 4. Diplotene 5. Diakinesis

Step 1: Leptotene

• Replicated chromosomes begin to condense and become simple (look less like “noodle soup”)

• chromosomes become visible as thin, narrow threads

• Homologous chromosomes

Step 2: Zygotene

• Homologous chromosomes come together; they are “yoked” to each other (zip up)

• Synapsis Begins (pairing of homologous chromosomes)

Step 3: Pachytene

• CROSSING OVER occurs within this phase (AKA recombination)

• Homologous chromosomes are held together

• Tetrads form (Bivalents)—Four chromatids (Two homologous chromosomes with two sister chromatids each)

• Bivalent= tetrad has formed and crossing over occurred

Step 4: Diplotene

• Chromosomes begin to “Unzip” as the move apart slightly

• Tetrads remain held together at points called chiasmata, visible evidence of crossing over

• Sister chromatids now have recombined segments from both maternal and paternal chromosomes

• Synaptonemal complex dissociates

Step 5: Diakinesis

• Final stage of prophase I

• Chromosomes are maximally condensed

• Nuclear envelope dissociates

• Cell is ready to go to Metaphase I

Meiosis I: Reduction division: Metaphase I

• Tetrads (Paired homologous chromosomes, NOT individual) line up on metaphase plate

• NOTE: Not the same as metaphase in mitosis (individuals lined up in mitosis)

Meiosis I: Reduction division: Anaphase I

• Homologous chromosome PAIRS separate

• One chromosome of each pair moves to opposite poles

• Sister chromatids remain attached at centromeres

• Cells now have HALF the chromosome count but full DNA content of starting cell

Meiosis I: Reduction division: Telophase I

• Nuclear envelopes may reform (if interkinesis occurs)

• chromosome may begin to decondense

Meiosis I: Reduction division: Telophase I —> CYTOKINESIS

• cleavage furrow forms, dividing cytoplasm

• produces two haploid cells (each with n chromosomes, but each chromosome still consists of two sister chromatids)

• after cytokinesis I, cells are haploid; one chromosome from each homologous pair

Meiosis II (similar to mitosis): Prophase II

• only happens in cells that went through INTERKINESIS

• All other cells proceed directly to Metaphase II

Chromosomes recondense

Nuclear envelope breaks down

Spindle fibers form

Meiosis II (similar to mitosis): Metaphase II

• Individual replicated chromosomes (Still consisting of TWO sister chromatids) line up on metaphase plate

• Not tetrads, these are individual chromosomes (like in mitosis)

Meiosis II (similar to mitosis): Anaphase II

• SISTER chromatids finally separate

• Individual chromatids (now counted as individual CHROMOSOMES) move to opposite poles

Meiosis II (similar to mitosis): Telophase II

• Nuclear envelopes reform

• Chromosomes decondense

Meiosis II (similar to mitosis): Telophase II—> CYTOKINESIS II

• Cell divides, producing two daughter cells

• FROM the two cells entering MEIOSIS II, Four total haploid cells result

Spermatogenesis

• Occurs in the testes

• Follows meiosis exactly as diagrammed

• 1 diploid cell—> 4 viable haploid sperm cells

• Begins only after puberty

• occurs continuously after puberty through death

• all four products viable and functional

Stages:

Primary Spermatocyte

Secondary Spermatocyte

Spermatids

Mature sperm cells

Primary Spermatocyte

• Diploid Cell entering Meiosis I

• Undergoes meiosis I with cytokinesis

Secondary Spermatocyte

• Haploid cells produced after Meiosis I

• Evidence of Interkinesis: Nuclei reform, chromosomes decondense briefly to “noodle soup” state

• Each then undergoes meiosis II

Spermatids

• Haploid cells produced after meiosis II cytokinesis is complete

• immature sperm cells

• Later mature into small and highly motile sperm cells within the epidymidis

Oogenesis

• Occurs in the ovaries

• Does NOT follow meiosis exactly; differs in the way that the cytoplasm splits (unevenly)

• 1 diploid cell—> 1 viable haploid egg cell (plus polar bodies)

Stages:

Primary Oocyte

Secondary Oocyte, first polar body

Mature Ovum, second polar body

Primary Oocyte (stage 1)

• Diploid cell arrested in prophase I from before birth until ovulation

• Remains in arrested state until puberty/menarche

Oogenesis: After Meiosis I (stage 2)

• After primary oocyte completes Meiosis I

• Cytokinesis is asymmetric/unequal

• produces TWO haploid cells of (very) different sizes

1. Secondary Oocyte (larger cell)

• receives most of cytoplasm, organelles, nutrients

• contains sufficient resources to reach next checkpoint

• Will complete Meiosis II only IF FERTILIZED

2. First Polar Body (smaller cell)

• receives minimal cytoplasm

• contains genetic material but insufficient resources to divide further

• eventually degenerates

Oogenesis: After Meiosis II (stage 3)

• secondary Oocyte only divides if fertilized

1. Mature Ovum (egg) (very large)

• receives most of cytoplasm again

• viable gamete ready for fertilization

2. Second Polar body (very small)

• degenerates

Wild type

Most COMMON allele, usually indicated by (+) sign

Any deviation from the wild type is “-”

Monohybrid Cross

• A cross between two heterozygous parents (Aa×AaAa×Aa) produces a 1:2:11:2:1 genotypic ratio (1 AA:2 Aa:1 aa1AA:2Aa:1aa) and a 3:13:1 phenotypic ratio.

The first law of inheritance

• The Law of Segregation states that every individual organism contains two alleles for each trait, and that these alleles segregate (separate) during meiosis such that each gamete contains only one of the alleles.

The second law of inheritance (Independent assortment)

unlinked or distantly linked segregating genes pairs behave independently.

• States that alleles for separate traits are passed independently of one another.

The third law of inheritance (Law of dominance)

• If the two alleles of an inherited pair differ (the heterozygous condition), then one determines the organism’s appearance and is called the dominant allele; the other has no noticeable effect on the organism’s appearance and is called the recessive allele.

• Thus, the dominant allele will hide the phenotypic effects of the recessive allele.