Genetics: Advanced Biology

Gregor Mendel

1822-1884

Father of Genetics

Mendel Model

Used peas

Many dichotomous traits

Mendelian Cross

Bread “truebreeding” plants based on different traits

Truebreeding

Parents with certain traits always produce offspring with same traits

Reginald Punnett

1907

First punnet square

Punnett Square

Diagram used to predict genotypes of offspring of particular breeding experiment

Mendel’s Law of Dominance

Indicates a dominant and recessive allele

Law of Segregation

Heredity is particular

Alleles separated during gamete formation

Mendel’s Law of Independent Assortment

Genes for a trait are inherited independently from other traits

Violations of independent assortment

Linkage: genes that are physically close together in chromosomes

Crossover: close genes are recombined together

Incomplete Dominance

Expression of two contrasting alleles such that the individual displays an intermediate phenotype

Codominance

Complete and simultaneous expression of both alleles for the same characteristic

Sex Linked Traits

Traits from genes on X & Y chromosomes

Female - XX

Male- XY

Lethal Alleles

A gene that shortens life expectancy

Hugo DeVries

Discovered Gene & Mutation

Chromosomal Theory of Inheritance

Chromosomes carry the unit of heredity-genes

T.H. Morgan

Discovered XY chromosomes, eye color directly linked to sex, =>violates Mendel’s law of independent independent assortment

Alfred Sturtivant

Student of T.H. Morgan

Created first genetic map of genes

Karyotype

Individual’s chromosome number and appearance

Trisomy 21

Extra 21st chromosome

Non-disjunction => sister chromatids fail to separate in meiosis

Trait

Variation in the physical appearance of a heritable characteristic

Phenotype

Observable traits expressed by an organism

Allele

Gene variation that arise by mutation and exist at the same relative locations on homologous chromosomes

Dominant Allele

Trait that is expressed over another allele

Recessive Allele

Trait that is not expressed when paired with a dominant allele

Genotype

Underlying genetic makeup, consisting of both physically visible and non-expressed alleles

Heterozygote

Individual having two different alleles of a particular gene

Zygote

Single cell formed when a sperm cell fuses with an egg cell

Locus

Position of a gene on a chromosome

Wildtype allele

Most common allele of a gene in a natural population

Mutant Allele

Gene variant that differs from the standard or wildtype allele

Genetic Crossing Over

Exchange of genetic material between non-sister chromatids resulting in chromosomes that incorporate genes from both parents

Mutation

Variation in the nucleotide sequence (DNA) of a genome

Karyokinesis

Division of a cell nucleus during mitosis

Non-disjunction

When sister chromatids fail to separate in meiosis

Rosalind Franklin

Used x-ray diffraction through x-ray crystallography

Created photo 51

Photo 51

The missing link for discovery of actual genetic structure

James Watson & Francis Crick

Discovered the double helix structure of DNA

Central Dogma of Biology

DNA to RNA to Proteins

Process of Central Dogma

Transcription to mRNA processing to Translation

Transcription

The production of a RNA strand from a DNA template

Transcription: Initiation

Promoters of DNA sequences allow RNA Polymerase, Transcription Factors, and TATA Binding Protein bind to the DNA chain to initiate transcription.

Enhancers

Increase transcription

Silencers

Decrease transcription

Transcription: Elongation

RNA polymerase synthesizes mRNA by adding complimentary RNA nucleotides (A,U,G,C) into a chain in a 5’ to 3’ direction

Transcription: Termination

Cuts of the mRNA strand by either a cleavage cut or hair pin formation

mRNA Processing Qualities

5’ cap

PolyATail

Intron Splicing

PolyATail Qualities

Long chain of A nucleotides added to 3’ end of the mRNA strand

Stabilizes RNA

Prevents degradation of mRNA

5’ cap (Methylation Cap)

Added to 5’ end

Mediates splicing

Allows mRNA to be exported to the cytoplasm

Meselson & Stahl Experiment

Discovered DNA replication is semi conservative

Proteins of DNA Replication

Helicase

Topoisomerase

Single Strand Binding Protein

Primase

DNA Polymerase

DNA Ligase

Helicase

Separates DNA strand

Topoisomerase

Prevents overwinding of DNA

Single Strand Binding Protein

Prevents helix form reforming

Primase

Synthesizes RNA primer

DNA Polymerase

Synthesizes new daughter DNA

DNA Ligase

Seals gaps between Okazaki Fragments

Okazaki Fragments

Formed from the lagging strands of DNA replication going 3’ to 5’

DNA Replication Picture

Type of Mutations

Point Mutations

Frameshift Mutations

Chromosomal Mutations

Point Mutations

Silent- non change in amino acid sequence

Missense- amino acid is substituted

Nonsense- a stop codon is subsitituted

Frameshift Mutations

results in a shift of a reading frame which causes wrong insertions or deletions

Chromosomal Mutations

Translocation- section of 1 chromosome ends on a different chromosome

Inversion- flipping of sections of chromosomes

Fusions- blending

Duplication- too many copies

Chromosomal Crossover

Nondisjunction- too many in a cell

Deletion- partial deletion of a chromosome

Intron Splicing

Noncoding introns are cut out the mRNA leaving only the coding positions

Translation (Protein Synthesis)

Decodes mRNA to produce polypeptides where ribosomes catalyze the reaction

Translation: Initiation

mRNA attaches to a small ribosomal subunit and a start codon with the appropriate anticodon attaches, a large ribosomal subunit will then attach

Translation: Elongation

tRNA brings amino acids matching each coding pair, an amino acid chain grows using peptidyl transferase

Translation: Termination

A stop codon is sensed and the process stops, the amino acid chain is sent to the Endoplasmic Reticulum for processing