Heredity

Mendelian Genetics

Introduction to Genetics GENETICS – branch of biology that deals with heredity and variation of organisms. Chromosomes carry the hereditary information (genes) Genes  DNA  RNA  Proteins

Chromosomes (and genes) occur in pairs Homologous Chromosomes (1 from mommy and 1 from daddy) Unique combinations of genes occur in sexual reproduction

Terminology you need to know: Gene – a unit of heredity; a section of DNA sequence encoding a single protein. Alleles – two genes that occupy the same position on homologous chromosomes and that cover the same trait (like ‘flavors’ of a trait).

Homozygous – having identical genes (one from each parent) for a particular characteristic. Heterozygous – having two different genes for a particular characteristic Blue is from father Red is from mother HomozygousAA aa Heterozygous Aa

Dominant – the allele of a gene that masks or suppresses the expression of an alternate allele Recessive – an allele that is masked by a dominant allele

Phenotype – the physical appearance of an organism. Genotype – the genetic makeup of an organisms

Monohybrid cross Parents differ by a single trait. Crossing two pea plants that differ in stem size, one tall one short T = allele for Tall t = allele for dwarf TT = homozygous tall plant t t = homozygous dwarf plant T T  t t

Punnett square A useful tool to do genetic crosses For a monohybrid cross, you need a square divided by four…. Looks like a window pane… We use the Punnett square to predict the genotypes and phenotypes of the offspring.

Using a Punnett Square TT and t t T T  t t STEPS: 1. determine the genotypes of the parent organisms 2. write down your "cross" (mating) 3. draw a p-square Parent genotypes: TT and t t Cross T T  t t

Punnett square 4. "split" the letters of the genotype for each parent & put them "outside" the p-square 5. determine the possible genotypes of the offspring by filling in the p-square 6. summarize results (genotypes & phenotypes of offspring) T T T t Genotypes: 100% T t t Phenotypes: 100% Tall plants

DNA

What is DNA? 1. Organic molecule 2. Nucleic acid

Where is it located? 1. Nucleus 2. Chromosomes X DNA

Structure of DNA Nucleotides a. Phosphoric Acid b. Deoxyribose sugar c. Nitrogenous bases: Adenine-Thymine Guanine-Cytosine 2. Ladder Shape 3. Double strand, helix twist

Transcription: mRNA is copied off of DNA In nucleus Steps: DNA untwists DNA unzips RNA codons line up

Transcription: mRNA DNA Code A T C G U A G C I I I mRNA has: Ribose sugar Uracil instead of thymine bases Nuclear membrane allows it to leave! mRNA A T C G U A G C I I I DNA Code

Translation Conversion of the message (mRNA Code) Into a protein By the ribosome factories

Replication to Proteins

Mitosis

Mitosis Is the division of the cell’s nucleus. Cells under go mitosis for a number of reasons including: Growth and repair Increased efficiency (Surface to volume ratio) Better communications with the cell Mitosis is apart of the cell’s life cycle

M - Mitosis G1 - Growth, normal activities. M G2 S – DNA replication G2 – Preps for mitosis M - Mitosis S

Phases of Mitosis Prophase Metaphase Anaphase Telophase Cytokinesis

Mutation

Mutation Any change that occurs in the DNA sequence Can be caused by errors in replication, transcription, cell division, or by external factors. Mutations can be beneficial or harmful

Locations of Mutations Reproductive cell - The altered gene becomes part of the offspring. Body (somatic) cell – Altered gene results in changes in a single cell. May result in cancer. Will not be passed to offspring.

Types of Mutations

Point Mutation

Translocation

Deletion