Structure and FunctionStructure and Functionof Geneof Gene(part I)(part I)

Gregor MendelGregor Mendel One of the pioneers in geneticsOne of the pioneers in genetics Used scientific approach to understand Used scientific approach to understand

genetic features:genetic features:• Character: is a heritable feature like Character: is a heritable feature like

flower colorflower color• Trait: Each variant for a characterTrait: Each variant for a character

Gregor Mendel in 1857Gregor Mendel in 1857 started to started to experiment with:experiment with:• Pea PlantsPea Plants

Traits:

Character:

Character Dominant traits Recessive traits

1857 Experiment

To explain his results, Mendel formulated a To explain his results, Mendel formulated a hypothesis that included the following:hypothesis that included the following:

1. In the organism there is a pair of “factors” that controls the appearance of a given characteristic. (We call them genes.)

2. The organism inherits these “factors” from its parents, one from each.

5. If an organism has two unlike factors (we call them alleles) for a characteristic, one may be expressed to the total exclusion of the other (dominant vs recessive).

4. When the gametes are formed, the “factors” separate and are distributed as units to each gamete. This statement is often called Mendel's rule of segregation.

3. Each is transmitted from generation to generation as a discrete, unchanging unit. (The wrinkled seeds in the F2 generation were no less wrinkled than those in the P generation although they had passed through the round-seeded F1 generation.)

Mendel’s principle of SegregationMendel’s principle of Segregation

Pairs of alleles segregate (separate) Pairs of alleles segregate (separate) during gamete formation; the fusion during gamete formation; the fusion of gametes at fertilization creates of gametes at fertilization creates allele pairs againallele pairs again

Ex: Tt organismEx: Tt organism• Each gamete gets either T Each gamete gets either T oror t, but not both t, but not both

Mendel did not stop here… Mendel did not stop here…

He went on to cross pea varieties that He went on to cross pea varieties that differed in differed in six other qualitative traitssix other qualitative traits. In . In every case, the results supported his every case, the results supported his hypothesis. hypothesis.

He crossed peas that differed in He crossed peas that differed in two two traitstraits. He found that . He found that the inheritance of the inheritance of one trait was independent of that of the one trait was independent of that of the otherother and so framed his second rule: the and so framed his second rule: the rule of independent assortmentrule of independent assortment. .

Mendel’s principle of Independent Mendel’s principle of Independent AssortmentAssortment

By then doing an F1 cross (RrYy x By then doing an F1 cross (RrYy x RrYy) Mendel showed that the allele RrYy) Mendel showed that the allele for yellow (Y) didn’t always end up in for yellow (Y) didn’t always end up in the same gamete with the allele for the same gamete with the allele for round (R)round (R)

Genes for different traits can Genes for different traits can segregate independently during the segregate independently during the formation of gametesformation of gametes

Animal InheritanceAnimal Inheritance

Human InheritanceHuman Inheritance

Mendel’s ModelMendel’s Model Alternative versions of Alternative versions of

genes account for variation genes account for variation in inherited charactersin inherited characters• Alleles are alternative Alleles are alternative

versionsversions• Chromosome Chromosome Gene Gene

LocusLocus For each character, an For each character, an

individual inherits 2 alleles individual inherits 2 alleles (P1 and P2):(P1 and P2):

Two alleles being different Two alleles being different have dominant or recessive have dominant or recessive allelesalleles

Dominant allele is Dominant allele is expressedexpressed

Structure and FunctionStructure and Functionof Geneof Gene(part II)(part II)

What is Inheritance?What is Inheritance?

Passing on genetic information from Passing on genetic information from parents to offspringparents to offspring

Humans have 23 pairs of Humans have 23 pairs of chromosomes (46 total)chromosomes (46 total)• 1 of each pair is from one parent and 1 of each pair is from one parent and

the other is from the other parentthe other is from the other parent

ChromosomesChromosomes

Chromosomes, threadlike structures, Chromosomes, threadlike structures, first observed by Nageli in 1842. first observed by Nageli in 1842.

Long strands of DNA that carry the Long strands of DNA that carry the genetic information on building and genetic information on building and sustaining a living human being.sustaining a living human being.

Each chromosome contains many Each chromosome contains many genesgenes

What is a Gene?What is a Gene?

A segment of a chromosome that A segment of a chromosome that containing the code for a single containing the code for a single protein (enzyme)protein (enzyme)- The enzyme causes a chemical reaction - The enzyme causes a chemical reaction that allows a trait to be expressed.that allows a trait to be expressed.ie. Production of a pigmentie. Production of a pigment

Something that stated by Mendel as Something that stated by Mendel as “factor”“factor”

Round vs WrinkledRound vs Wrinkled

Dominant allele round codes for Dominant allele round codes for enzymeenzyme that converts sugar that converts sugar starch starch

Recessive allele have defective enzymeRecessive allele have defective enzyme• Sugar accumulatesSugar accumulates• Water diffuses in the seedWater diffuses in the seed• Seeds swellSeeds swell• Mature seed when dried becomes wrinkledMature seed when dried becomes wrinkled• One dominant allele produces enough One dominant allele produces enough

enzymeenzyme• Both homozygous dominants and Both homozygous dominants and

heterozygotes produce enough enzymeheterozygotes produce enough enzyme

AllelesAlleles Alleles are alternate forms of a Alleles are alternate forms of a

genegene• HomozygousHomozygous individuals have two individuals have two

identical alleles for a traitidentical alleles for a trait

ex.: AA or aa organism• HeterozygousHeterozygous individuals have two individuals have two

different alleles for a traitdifferent alleles for a trait

ex.: Aa organismex.: Aa organism

Chromosomes are threadlike structures

composed of DNA molecules

Nucleus (center of cell) contains chromosomes and genes

A gene, a segment of DNA (spiraled double

chain) containing the hereditary

code

The body contains trillions

of cells

Cell, chromosome and gene (DNA)

chromatin

The Structure of ChromosomeThe Structure of Chromosome

Nucleotides --> DNA --> Gene --> Nucleotides --> DNA --> Gene --> Chromosome Chromosome

Human DNA is ~ 2 meters long. The Human DNA is ~ 2 meters long. The nucleus of DNA is about 6 µM in diameter.nucleus of DNA is about 6 µM in diameter.

So, how the very long DNA is So, how the very long DNA is packed into a very small packed into a very small

nucleus?nucleus?

fatchiyah, JB UBfatchiyah, JB UB

Chromosome StructureChromosome Structure

Type of chromosome structureType of chromosome structure

MetacentricChrom. 1

AcrocentricChrom. 14

SubmetacentricChrom. 9

1. The short arm is designated as p and the long arm as q.

2. The centromere is the location of spindle attachment and is an integral part of the chromosome.

3. It is essential for the normal movement and segregation of chromosomes during cell division.

The ideogram is basically a "chromosome map" showing the relationship between the short and long arms, centromere (cen). The specific banding patterns are also illustrated. Each band is numbered to aid in describing rearrangements.

What molecule transmitting What molecule transmitting genetic inheritance from genetic inheritance from parents to offspring ? parents to offspring ?

DNADNA(Deoxyribose Nucleic Acid)(Deoxyribose Nucleic Acid)

THE STRUCTURE OF DNA

nucleoside

base

sugar

DNA: terminology

nucleotides (nucleoside mono-, di-, and triphosphates)

sugarphosphate(s)

base

sugar

1. DNA is double stranded2. DNA strands are antiparallel3. G-C pairs have 3 hydrogen bonds4. A-T pairs have 2 hydrogen bonds5. One strand is the complement of the other6. Major and minor grooves present different

surfaces7. Almost all cellular DNA is B-DNA8. B-DNA has ~10.5 bp/turn of the helix

DNA: structure

Gene expression in eucaryotes and procaryotes

Molecular Definition of GeneMolecular Definition of Gene The entire nucleic acid sequence that The entire nucleic acid sequence that

is necessary for the synthesis of a is necessary for the synthesis of a functional protein and RNAfunctional protein and RNA

Coding region (exon and intron) + Coding region (exon and intron) + Regulatory sequences (e.g. Regulatory sequences (e.g. promoter=promoter=the site where RNA polymerase binds the site where RNA polymerase binds

prior to the initiation of transcriptionprior to the initiation of transcription))

Basic Gene StructuresBasic Gene Structures Eukaryotic genesEukaryotic genes

• Exons,introns,Exons,introns,• translation starts and stops, splice (donor/acceptor) translation starts and stops, splice (donor/acceptor)

junctionsjunctions

Basic Gene StructureBasic Gene Structure

Prokaryotic genesProkaryotic genes• coding regions, non-coding regionscoding regions, non-coding regions• translation starts and stopstranslation starts and stops

gene genegenepromoter

start stop

Prokaryotic genes are easier to identify than eukaryotic genes because of the simplicity of their gene structure and the density of genes in the genome