Genetics: The Science of Heredity Mendel’s Work Probability and Heredity The Cell and Inheritance The DNA Connection Table of Contents

Genetics: The Science of Heredity Heredity, Traits and Genetics *Heredity is the passing of traits from parent to offspring *A trait is a characteristic of an organism, such as hair color, eye color, etc. *Genetics is the scientific study of heredity.

Genetics: The Science of Heredity The Father of Modern Genetics *Gregor Mendel outlined the basic laws of heredity. *Mendel was an Austrian monk born in *Experimented with garden pea plants *Presented the first paper on genetic research in 1866 titled, “Experiments with Plant Hybrids”

Genetics: The Science of Heredity Mendel chose garden pea plants for his experiments. Why? Mendel’s Experimental Garden

Genetics: The Science of Heredity *Pea plants usually self-pollinate, producing purebred plants. *Mendel found a way to cross-pollinate them so he could mix traits. *Easy to grow large numbers of plants. *Many different traits such as height, seed color, seed shape, pod color, pod shape, and flower color can be easily studied.

Genetics: The Science of Heredity wrinkled seeds Side or end flowers

Genetics: The Science of Heredity - Mendel’s Work How did he do it? Gregor Mendel crossed pea plants that had different traits. The illustrations show how he did this.

Details of Mendel’s First Experiment Mendel’s first step was to cross pure tall plants with pure short plants. X What were his results?

The first generation of offspring were all tall. X How can this be? P generation F 1 generation

Genetics: The Science of Heredity Mendel’s Explaination In pea plants, tall traits overpower short traits. Each plant, although it looked tall, was hiding a factor for short height. Will the short trait reappear in the next generation?

To find out, Mendel now crossed tall plants of the first generation with each other. x What were his results?

In the second generation, the offspring were both tall and short. Tall outnumbered short 3 : 1 X F 1 generation F 2 generation

Genetics: The Science of Heredity - Mendel’s Work In all of Mendel’s crosses, only one form of the trait appeared in the F 1 generation. However, in the F 2 generation, the “lost” form of the trait always reappeared in about one fourth of the plants.

Genetics: The Science of Heredity Mendel’s Conclusion Tall is a dominant factor for height since it overpowers or hides the short factor. Short is a recessive factor for height since it appears to disappear if the tall factor is present. We now call these “factors” alleles. Do not use for vocab journal… definitions will come later

Genetics: The Science of Heredity - Mendel’s Work Dominant and Recessive Alleles Mendel studied several traits in pea plants.

Genetics: The Science of Heredity Traits, Genes and Alleles Sometimes the words "gene", "allele" and "trait" seem to be used to mean the exact same thing. Although they all are closely related, there is a difference between genes, alleles, and traits.

Genetics: The Science of Heredity A trait is a characteristic of an organism, such as tall height. A gene is a small section of DNA on a chromosome that controls a trait. (Mendel didn’t know about chromosomes). The different forms a gene may come in are its alleles (example—short or tall are the alleles for the gene that controls the height of a plant). Homologous Chromosomes GeneAlleleTrait Tall

Genetics: The Science of Heredity Mendel showed that organisms have two alleles for every trait. (One that we get from mom and one that we get from dad). He also showed that these alleles can be either dominant or recessive. Capital letters are used to represent dominant alleles and lower case letters are used to represent recessive alleles.

Genetics: The Science of Heredity Dominant traits will be seen even if there is only one dominant allele in the pair. TT = tall plants Tt = tall plants Recessive traits will only be seen when both recessive alleles are present in the pair. tt = short plants This explains the 3:1 ration of tall to short plants observed by Mendel. **USE FOR VOCAB JOURNAL!

Genetics: The Science of Heredity Heterozygous and Homozygous An individual with two alleles for a trait that are exactly the same (TT or tt) is said to be homozygous or “pure” for that trait. An individual with two different alleles for a trait (Tt) is said to be heterozygous or “hybrid” for that trait.

Genetics: The Science of Heredity Genotypes and Phenotypes Genotype is an organism’s genetic make-up: it includes hidden traits and is represented by letters: Examples: TT Tt or tt Phenotype is the physical trait that you see in an organism: it is a description Examples: tall plants or short plants

Genetics: The Science of Heredity - Probability and Heredity Phenotypes and Genotypes

Genetics: The Science of Heredity Remember, Mendel did not know how factors were passed from parent to offspring. In 1903, Walter Sutton discovered that Mendel’s “factors” were actually genes carried on chromosomes. These genes are passed to the offspring in the sperm and egg cells produced during meiosis.

Genetics: The Science of Heredity Sutton discovered this while studying the development of sperm and egg cells in grasshoppers. This is now known as the chromosome theory of inheritance.

Genetics: The Science of Heredity Chromosomes Click the Video button to watch a movie about chromosomes. - The Cell and Inheritance

Genetics: The Science of Heredity - The Cell and Inheritance A Lineup of Genes Chromosomes are made up of many genes joined together like beads on a string. The chromosomes in a pair may have different alleles for some genes and the same allele for others.

Genetics: The Science of Heredity When a pair of chromosomes separate during meiosis, the two alleles for a trait move into separate sex cells. Ee = parent genotypeee = parent genotypeEE = parent genotype

Genetics: The Science of Heredity The genotype of the offspring will be determined by which sperm cell fertilizes which egg cell. e E Ee Ee = genotype of offspring

Genetics: The Science of Heredity Punnett Squares Punnett squares can be used to show the possible ways that genes can combine at fertilization

Genetics: The Science of Heredity - The Cell and Inheritance A Punnett square is actually a way to show the events that occur at meiosis.

Genetics: The Science of Heredity Monohybrid Cross A Punnett Square that shows only one trait is known as a Monohybrid Cross.

Genetics: The Science of Heredity TT t t T tT tT tT t T tT tT tT t The only possible combination for the offspring of these two parents is one tall allele (T) and one short allele (t). All offspring will be hybrid (heterozygous) tall. Genotype = Tt Phenotype = tall Example: TT x tt

Genetics: The Science of Heredity Let’s look at another example: T t x T t T t T t T T tT t T t t There are 3 combinations for the offspring of these two parents. They occur in the following ratios: Pure (homozygous) tall TT = 25% Hybrid (heterozygous) tall Tt = 50% Pure (homozygous) short tt = 25%

Genetics: The Science of Heredity What do you actually see? 75% tall plants and 25 % short plants.

Genetics: The Science of Heredity Mendel’s Law of Independent Assortment Mendel discovered that it was possible to study more than one trait at a time. Example: There are 4 possible outcomes for the gametes. One letter does not affect the selection of the other.

Genetics: The Science of Heredity Dihybrid Crosses show two traits: Example: Rr Yy x Rr Yy R = round seeds Y = yellow seeds r = wrinkled seeds y = green seeds RYRyrYry rY Ry RY RRYYRRYY RRYyRRYy RRYyRrYYRrYyRrYy RrYy RryyRrYyRrYy RrYYRrYY rrYyrrYy rrYY RrYy rryyrryy rrYy RRyyRRyy 9 = round/ yellow 3 = round/ green 3 =wrinkled/ yellow 1 = wrinkled/ green

Genetics: The Science of Heredity Codominance Codominance occurs when neither allele in the pair is dominant over the other. Example: Pure Red Flowers X Pure White Flowers Result: All Pink Flowers

Genetics: The Science of Heredity WW RW RR X

Genetics: The Science of Heredity Punnett Squares for codominance do not use lower case letters, since neither trait is dominant. Example: RR X WW RR W W RWRW RWRWRWRW RWRW All offspring are PINK

Genetics: The Science of Heredity - Probability and Heredity Codominance Another example of codominance shows each trait appearing together rather than a blending.

Genetics: The Science of Heredity Mutations Without correctly coded proteins, an organism can’t grow, repair, or maintain itself. Sometimes mistakes happen in the genetic code. Any permanent change in a gene or chromosome of a cell is called a mutation.

Genetics: The Science of Heredity Mutations can: *be harmless, beneficial, or harmful *happen randomly or be caused by an outside factor (x-rays, radiation, chemicals etc.) *add variety to a species over time

Genetics: The Science of Heredity Three Types of Mutations *Substitution—one base pair is substituted for another. *Deletion—one base pair is omitted *Addition—one base pair is added

Genetics: The Science of Heredity - The DNA Connection Mutations Mutations can cause a cell to produce an incorrect protein during protein synthesis. As a result, the organism’s trait, or phenotype, may be different from what it normally would have been.