Fundamentals of Genetics

HOMEWORK YOUR JOB IS TO GO TO THIS WEBSITE and LEARN ABOUT PUNNETT SQUARES http://www.mhhe.com/biosci/genbio/virtual_labs/BL_05/BL_05.html Your evidence for the ACS will include the finished product of 3 punnett squares that you will need to describe and draw and bring to class tomorrow.

Gregor Mendel (1822-1884) Monk from Austria He bred pea plants in monastery gardens and used math to interpret his findings He is the “Father of Genetics” Even though he was never recognized in his lifetime!

Mendel’s Garden Peas Mendel observed seven characteristics when using purebred pea plants. Each characteristic trait occurred in two contrasting alleles. Traits – a distinguishing characteristic that is inherited such as eye color, leaf shape and tail length. Allele – different forms of a trait

Mendel’s Observations Mendel observed 7 characteristics of pea plants. ex: - seed color (green or yellow) - seed texture (smooth or wrinkled) - flower color (purple or white) He used his knowledge of statistics to analyze his observations. Crossed plants (mated), collected seeds, recorded observations, then planted seeds, then recorded new plant characteristics.

Mendel’s Methods Pollination – occurs when pollen grains produced in the male reproductive parts of a flower (called anthers) are transferred to the female reproductive part of a flower (called stigma). Self-pollination – occurs when pollen is transferred from the anthers of a flower to the stigma of either the same flower or a flower on the same plant.

Cross-pollination – involves pollen transfer with flowers of two separate plants. First Mendel snipped off the anthers Then he dusted the stigma with pollen taken from the desired father.

Finally he tied bags over the flowers to keep out any stray pollen. This gave him control over the pollination of his pea plants (no wind or insects could interfere!)

He observed that purple-flowering plants grew from the seeds of purple plants, but… he noticed that some white-flowering plants also grew from the seeds of purple-flowering plants. Mendel wanted to find an explanation for such variations.

Mendel’s Laws AKA – Patterns of Inheritance

Mendel Discovered Dominance 1st Cross= pure Tall x pure Short Tall  All Tall Short X Tallness = Dominant Short = Recessive

Dominance- allele expressed when present in genotype Recessive- allele expressed ONLY when two copies are present

Now Breed the Hybrid 2nd Cross= hybrid Tall x hybrid Tall. Plants self pollinate (self-fertilize) Hybrid- containing contrasting alleles

Recessive trait reappears!!! Tall x Tall  ? Results in math: 3/4 tall : 1/4 short plant Recessive trait reappears!!!

Law of Segregation Organisms inherit two copies of each gene/trait = alleles. Alleles segregate (separate) during the formation of sperm and eggs. Organism donates ONE copy of each gene in fertilization.

Alleles Def: Allele is an alternative form of a gene (ex: tall and short for PLANT HEIGHT) One allele T is for tallness One allele t is for shortness T allele is dominant over t allele. Tt = Tall TT = Tall tt = short Certain traits do not blend!! (no medium height)

Same Phenotype Different Genotype TT Tt

Homozygous – when both alleles of a pair are alike. (Ex: TT or tt) (can be homozygous dominant or homozygous recessive) Heterozygous – when the two alleles in the pair are different. (ex: Tt)

Punnet Square A grid system to predicting all possible genotypes and phenotypes that result from a cross. Is a shorthand way of showing how the gametes behave in a cross.

Monohybrid Cross – a cross between one trait (ex: plant height, OR hair texture) t T Tt tt t t

Testcross- cross between an organism with homozygous recessive genotype and a second organism with an unknown genotype. The offspring results will show whether the organism with unknown genotype is heterozygous or homozygous dominant.

Dihybrid Cross a cross between two traits (ex: plant height and seed color) Mendel’s question… are traits inherited together? Ex: Do people with Blond hair always have blue eyes? Do purple flowers always make smooth seeds? Do seeds that are round have to be yellow???

2. Law of Independent Assortment Traits segregate (separate) independently during the formation of sperm and eggs. They then come together again in the new offspring (kid)