Genetics: The Science of Heredity What is Heredity?

What did Mendel observe? Gregor Mendel: Known as the Father of Genetics, he unlocked the key to understanding heredity using pea plants. He was able to obtain predictable, repeatable results using plants that could both self-pollinate & cross-pollinate. Heredity the passing of traits/physical characteristics from parents to offspring Genetics the scientific study of heredity Fertilization the joining of egg and sperm cell (the beginning of the formation of new organism)

How do alleles affect inheritance? Genes segments of DNA that carry hereditary instructions on chromosomes & passed from parent to offspring (factors that control a trait) Alleles alternative forms of a gene that govern the same characteristics (ex. Eye color) How do alleles affect inheritance? An organism's traits are controlled by the alleles it inherits from its parents. Some alleles are dominant, while other alleles are recessive. Dominant trait trait observed when at least one dominant allele for a characteristic is inherited Recessive trait trait that is apparent only when 2 recessive alleles for the characteristic are inherited Homozygous/Purebred having 2 copies of the same allele for a trait (ex. HH or hh) Heterozygous/Hybrid having 2 different alleles for a trait (ex. Rr or RW)

Probability & Heredity How is probability related to inheritance? In a genetic cross, the combination of alleles that parents can pass to an offspring is based on probability = the mathematical chance that an event will occur Punnett Square (designed by Reginald C. Punnett) a chart that shows all the possible ways alleles can combine in a genetic cross Parent generation (Purebred purple flowers - PP x Purebred white flowers - pp) P P p F2 generation (self pollination of the offspring from the F1 generation: Pp x Pp)   P p   P   What are phenotype & genotype? Genotype the inherited combination of alleles; genetic make up Phenotype an organism’s inherited appearance; visible appearance Pp = 100% purple PP Pp pp = 75% purple = 25% white (recessive trait reappears)

Patterns of Inheritance How are most traits inherited? Most traits are the result of complex patterns of inheritance. Codominance both alleles for a gene are expressed equally (and individually) Incomplete dominance one allele is only partially dominant (blending occurs) Multiple Alleles three or more possible alleles determine the trait (an organism can still only inherit 2 alleles for a gene, one from each parent, but there are more possible genotypes with multiple alleles than with just 2 alleles; example = blood type) Polygenic Inheritance more than one gene affects a trait (broad range of genotypes: human height, skin color, and eye color) Inherited Trait traits organisms are born with (height, freckles, eye color) Acquired Trait traits organisms acquire (language a person speaks, haircuts, piercings, tattoos)

How do genes and the environment interact?   Environmental factors can influence the way genes are expressed. Examples: slider turtles & temperature inherited ability and opportunity to learn tobacco smoke and gene triggers Changes in body cells cannot be passed on to offspring. Only changes in sex cells – eggs & sperm can be passed to offspring.

Chromosomes & Inheritance How are chromosomes, genes, and inheritance related?  According to the chromosome theory of inheritance, genes pass from parents to their offspring on chromosomes. Chromosome: coiled structure of DNA & protein that forms in the nucleus during cell division; passed from one generation to the next What happens during meiosis? Meiosis produces new cells with ½ the usual number of chromosomes. This process creates sex cells. The chromosomes are copied/duplicated only once & nucleus divides twice.