Central Dogma of Molecular Biology• DNA

– Stored information inside nucleus– Copied to make new cells = REPLICATION

• RNA– Copied from a piece of DNA (GENE) to make

a single protein = TRANSCRIPTION– Moves information from nucleus to cytoplasm

• Protein – Information from a single RNA used to make a

single protein = TRANSLATION

Base Pairing

• Complementary bases– A bonds to T– C bonds to G

• Complementary strands– Opposite strands of DNA

that can completely base pair to form a double helix

DNA Double Helix

Chromatin and Chromosomes

• Chromatin– DNA associated with proteins– Organizes and packages DNA

• Chromosome– Tightly coiled chromatin– Many cells have more than one chromosome– Humans – 46 chromosomes

DNA Replication

• Each strand of DNA can act as a template for the complementary strand

• Enzymes guide replication

• Enzymes pull apart the DNA strands• Enzymes add complementary nucleotides to

each strand

DNA Replication

Transcription

• Part of the DNA molecule is copied to make an RNA molecule

The Genetic Code and Genetics

• How does DNA encode for protein?– DNA – nucleotide subunits

• Nitrogenous bases = information

• 4 different nitrogenous bases

– Protein – amino acid subunits• 20 different amino acids

How are four nitrogenous bases translated into 20 different amino acids?

• Nucleotides form “words” called codons– Each codon codes for a different amino acid– A codon consists of 3 nitrogenous bases– 64 different combinations of codons– Only 21 needed (20 amino acids, 1 stop)

How is the code read?

Transfer RNA’s

• “Read” codons

• Bring amino acids to the ribosome

Mutations• Changes in DNA often but not always cause

changes in the protein for which it codes.

• Changing a single nucleotide has the potential to dramatically change a protein.

Gene

Homologous Chromosomes

Vocabulary• Allele

– Different versions of a gene– Make different versions of a protein

• Homozygous– Same allele on both homologous chromosomes

• Heterozygous– Different allele on each homologous chromosome– Often referred to as a hybrid

• Genotype– Total set of alleles which can be passed to the next

generation

• Phenotype– Observable appearance caused by different alleles

Naming Genes• All alleles of a gene use the same root letter or

word to indicate that it is the same gene• Dominant allele

– Phenotype expressed in heterozygous individual– Capitalized letter or word = dominant gene

• Recessive allele– Phenotype only expressed in homozygous

individual– Lower case letter or word = recessive gene

Gregor Mendel’s Law of Segregation

• Alleles of a gene segregate from one generation to another

• Exact reason not known by Mendel• Today we know assortment occurs during meiosis

Garden Pea

• Self-fertilize– Pollen from same flower

• Cross-fertilize– Pollen from different flower

• To cross is to fertilize (mate)

Heterozygous Cross

• Alleles– P

• Dominant

• Phenotype purple

– p• Recessive

• Phenotype white

Genotype Vs. Phenotype Ratio

Test Cross

• To cross an organism with an unknown genotype with an organism with a known phenotype

• PP or Pp X pp– Purple flower could be either PP or Pp– White flower must be pp

Multiple Alleles

Incomplete Dominance

Linked Genes

• Genes close together on the same chromosome

• Sort together during Meiosis

• Inherited together

Gregor Mendel’s Law of Independent Assortment

• Traits are transmitted to offspring independently of one another

• Traits that sort independently are on different chromosomes

Dihybrid Cross

• Seed Texture– R=round– r=wrinkled

• Seed Color– Y=yellow– y=green

Sex Chromosomes

• Humans– 46 total chromosomes

– 23 pairs• 22 pairs are called autosomes

– common to both males and females

• 1 pairs are called sex chromosomes– Females

» 2 X-chromosomes

– Males

» 1 X-chromosome and 1 Y-chromosome

Sex Determination

• SRY gene present on Y-chromosome triggers male pathway

• Female pathway is the default

• Hormones determine male and female sex characteristics

X-Linked Traits

• Male inherits only one X-chromosome– From which parent?– Males are Hemizygous for genes on X-

chromosome

• Female inherits two X-chromosome– One from each parent

Queen Victoria Pedigree

Dosage Compensation

• Both males and females require the same amount of protein coded for in their X-chromosomes– However…

• Females 2 X-chromosome

• Males 1 X-chromosomes

X-inactivation

• Female embryos inactivate one X-chromosome at random in each cell when they are 12-16 days old.

• Inactive X-chromosome is called a Barr Body

• Females are a mosaic

Calico Cats• Gene for coat color on X-chromosome

• Two alleles Brown and Black

Anhydrotic Dysplasia

• Sweat gland do not develop

• Heterozygous females are mosaics