Introduction to Heredity Passing On Information Section 5.1

Early Ideas Hippocrates (460-377 BCE)  seeds Aristotle (384-322 BCE)  male and female semen Helps us determine the likelyhood of inheriting certain traits

More Early Ideas William Harvey (1500’s)  epigenesis Stages of development based on mother’s experience Anton van Leeuwenhoek (late 1600’s)  “animalcules”

Even More Early Ideas 19th century  “blending theory” Charles Darwin sperm and egg mixed Result was a blend Had a lot of holes Charles Darwin Offspring had variations of parents’ traits Natural Selection

Finally an Answer… Gregor Medel (1822 – 1884), an Austrian monk Experimented on pea plants 3 reasons: Grow quickly Pollinate easily Definable traits Found 7 traits that had only two possible variations 1. Choosing an appropriate organism to study, 2. designing and performing the experiment correctly, 3. analyzing data properly

7 Traits Seed shape Seed colour Flower colour Flower position Pod colour Pod shape Height yellow purple green inflated tall round axial (side) white Terminal (side) yellow Constric-ted short Wrink-led green

Setting Up Mendel’s Experiment Needed a purebred How could he achieve this? Ended up with 14 purebreds Called process “true breeding” Purebred  desceding from a line of similar traits True breeding  breed two tall plants together that are tall (babies are 5 T 3 t), then breed two of those 2 tall ones breed (they have 4 T and 1 short)  keep going until all offspring are tall

Mendel’s First Experiment: A Monohybrid Cross P (Parent) generation Crossed pure tall with pure short Actual: 100% tall! Called them Filial generation or F1 generation Hybrid (a cross between two purebreds) Monohybrid (only one trait was involved)

Seed of F1 What actually HAPPENED in the seeds? Knew the seeds HAD to be hybrids Principle of Dominance Dominant trait is always expressed Recessive is present but not expressed What would blending predict Dominant trait is always expressed Recessive is latent (present but not expressed)  may be expressed if it’s the only trait present

The Next Generation Crossed two F1s  F2 generation Expected results? 75% tall, 25% short Mendelian ratio (3:1)

Definitions Gene vs Allele We use letters to represent alleles T = tall t = short What are the allele’s P generation Tall plants = TT Short plants = tt Homozygous Alternate  options Recess not altered and can still be passed on Gene represent the trait, allele represent what it could actually be (options) Homozygous = two alleles are the same

Hybrids Offspring (F1)generation Called these hybrids Heterozygous (Tt) Heterozygous means different or one of each

Mendel’s Conclusions Each parent starts with two hereditary genes These genes separate Only one is passed on to an offspring If the dominant gene is present in the offspring, it is expressed (regardless of recessive trait) Recessive gene expressed only if both recessive genes are present https://www.youtube.com/watch?v=Mehz7tCxjSE Part of chromosome that gives information about what trait should be expressed Ex. Gene for hair colour

Law of Segregation Law of Segregation states that: Inherited traits are determined by pairs of genes These genes segregate into gametes, with one gene in each We now know this is a result of: ___________ One from Dad, one from Mom They go through Meiosis, but they didn’t know that yet