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 Complementary strands 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 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

DNA Replication Enzymes pull apart the DNA strands Enzymes add complementary nucleotides to each strand

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 Homozygous Heterozygous Genotype Phenotype 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 Cross-fertilize Pollen from same flower Cross-fertilize Pollen from different flower To cross is to fertilize (mate)

Heterozygous Cross Alleles P p Dominant Phenotype purple 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 Seed Color R=round r=wrinkled 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