Genetics The study of how traits are inherited through the interactions of different types of genes.

Heredity The passing of traits from parent to offspring Genes on chromosomes generally control an organism’s form and function The different forms of a trait that a gene may have are called alleles Alleles are separated during the process called Meiosis, which is a component of sexual reproduction From one parent, the alleles may be the same or different for a particular trait and thus the offspring may receive either allele in combination with another allele from the other parent

Mendel-The Father of Genetics Austrian monk who served as the gardener for his monastery. Became curious about the connection between the color of a flower and the type of seed produced from crossbreeding. Traced one trait through several generations of pea plants. Used mathematical probability to explain the results

Mendel’s Experiments Mendel crossed plant with different expressions of a trait and found that the new plants all looked like one of the parents. He called these hybrids because the received different genetic information (alleles) for a trait form each parent. He hand pollinated purebred short plants with pollen from purebred tall plants and got all tall plants so he called the tall form dominant and the short form recessive because it disappeared, or was “covered up.”

Genotype and Phenotype Genotype, or genetic makeup is either purebred or hybrid. (3 possible types) Phenotype is the way the an organism looks and behaves as a result of its phenotype.(2 possible) Purebred organisms have either two dominant alleles or two recessive alleles. Hybrid organisms have one dominant and one recessive allele. Purebred and Hybrid organisms with the dominant allele will exhibit the dominant trait. Only purebred recessive organisms will exhibit the recessive trait.

Dominant vs. Recessive Many incorrectly assume that Dominant means stronger or more common. Dominant means that trait appears when that particular allele is present. The law of dominance explains that one trait (the dominant) is expressed in homozygous and heterozygous conditions. The recessive trait is expressed only in the homozygous condition.

Homozygous and Heterozygous Most cells have two alleles for every trait If the alleles are the same, the organism is considered homozygous. If the alleles are different, the organism is considered heterozygous. Homozygous = purebred Heterozygous = hybrid

Probability and Predictions Probability is a branch of mathematics used to predict the chance of something happening. Different possible outcomes will each have a percentage chance of occurring which is its probability. Mendel worked with nearly 30,000 plants over 8 years so the percentages of different possible outcomes yielded reliable patterns of probability.

Punnett Squares Punnett squares use letters as a code to represent alleles and show different possible combinations and outcomes. Uppercase letters represent dominant alleles and lowercase show recessive alleles T=tall t=short T t TT Tt tt

Making a Punnett Square In a Punnett square for predicting one trait, the letters representing the two alleles from one parent are written along the top of the grid with one letter per section. Those of the second parent are placed down the side of the grid, one per section. Each square of the grid is filled in with one allele from each parent. The combinations in each square represent the genotypes of possible offspring that parents can produce. Their probability is the percentage of the whole of each genotype.

More Punnett Square examples T=tall t=short T t Tt T=tall t=short T t Tt tt

Principles of Heredity Traits are controlled by alleles on chromosomes. An allele’s effect is dominant or recessive When a pair of chromosomes separates during meiosis, the different alleles for a trait move into separate sex cells