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Mendelian genetics. *Gregor Mendel is considered the father of genetics. *In 1843, at the age of 21, he became a monk in Austria where he was put in charge of tending the monastery garden. *In 1851, he was sent to the University of Vienna where he studied science, math, and statistics.

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*Gregor finished college and returned back to the monastery as a very well-educated monk. *He began working in the garden again and noticed several things.. *Many of the tall plants he grew produced tall offspring, while some produced short offspring. *Some of the plants with yellow seeds had offspring with yellow seeds, while others had green seeds. *Mendel believed that plants inherited their traits from their parents. He decided to see if he could find a predictable pattern to the way pea plants inherited traits.

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*Mendel developed pure strains of plants by self-pollinating plants with the trait he wanted. *The pure strains each had a contrasting trait. *He called these pure strains the P1 (parental ) generation.

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Plants reproduce when pollen from the anther is transferred to the stigma and the ovules are fertilized.

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*Mendel developed 14 pure plant strains. Each characteristic had two contrasting traits. *Mendel cross pollinated the pure strains and called the offspring the F1 (1 st filial) generation.

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*The F1 plants were then self-pollinated, and Mendel called their offspring the F2 (2 nd filial) generation. *Think of this as the parents, kids, & grandkids. *Gregor Mendel made thousands of crosses and found a predictable pattern. *In the F1 generation, the recessive trait was hidden. *In the F2 generation, the recessive trait re- appeared in a 3:1 ratio with the dominant trait. *Mendel concluded that there are three principles that control heredity.

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Mendels Principles of Heredity. Principle of Dominance when 2 forms of the same gene are present the dominant allele is expressed. Principle of Segregation in meiosis two alleles separate so that each gamete (sex cell) only receives one form of the gene. You get a trait either from your mother or father, not both. Principle of Independent Assortment each trait is inherited independently from other traits. Height and hair color are not connected.

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Genes. *Mendels factors are now called genes. *A gene is a segment of DNA on a chromosome that controls a hereditary trait. *Chromosomes occur in pairs. *One chromosome comes from each parent. *The gene segment on each chromosome is called an allele.

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*Dominant alleles are represented by a capital letters (T, R). *Recessive alleles are represented by lower case letters (t,r). *A homozygous dominant genotype (TT, RR) always shows the dominant trait. *A heterozygous dominant genotype (Tt, Rr) always shows the dominant trait, but is a carrier of the recessive trait. *A homozygous recessive genotype (tt, rr) always shows the recessive trait.

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*The genotype is the genetic makeup of the Individual and is expressed in letters (TT, Tt, tt). *The phenotype is what the individual actually looks like (tall, short). Genetic crosses. A monohybrid cross is a cross between individuals that involves only one pair of contrasting traits. (TT x Tt)

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1. Cross a plant that is homozygous dominant for the trait of height ( ) with a plant that is homozygous dominant for that trait ( )

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2. Cross a plant that is homozygous dominant for the trait of height ( ), with a plant that is heterozygous for that trait ( ).

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3. Cross a plant that is heterozygous for the trait of height ( ), with a plant that is heterozygous for that trait ( ).

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Testcross. *A testcross is the procedure in which an individual of unknown genotype is crossed with a homozygous recessive individual. *A testcross can determine the genotype of any individual whose phenotype is dominant. *For example, in rabbits, both of the genotypes BB and Bb result in a black coat. A black rabbit is found in your garden and you want to find out whether it is homozygous dominant (BB), or heterozygous (Bb). *You simply breed the mystery rabbit with a homozygous recessive rabbit.

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Determine the genotype of an unknown black rabbit by performing a test cross.

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Incomplete dominance. *Incomplete dominance occurs when two or more alleles influence the phenotype. *This result in a blending of traits in the offsprings phenotype. *In Japanese four oclock plants, both the allele for red flowers (R) and the allele for white flowers (R) influence the phenotype, but neither allele is dominant. *RR results in red flowers. *R R results in white flowers. *RR results in pink flowers which is a blending of the red and white traits.

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CROSS A RED 4 OCLOCK PLANT WITH A WHITE 4 OCLOCK PLANT. LIST THE OFFSPRING

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Dihybrid Crosses. *A dihybrid cross involves two pairs of contrasting traits, instead of one trait as in a monohybrid cross. *Predicting the results of a dihybrid cross is more complicated than predicting the results of a monohybrid cross because there are more possible combinations of alleles to work out. *A dihybrid cross such as TtRr X TtRr will yeild 16 offspring. *A heterozygous X heterozygous dihybrid cross always results in a 9:3:3:1 phynotypic ratio in the offspring.

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Genotypes 4/16- 2/16- 1/16- RatioPhenotypes 9 3 3 1 Dihybrid Cross Template Cross: Foil:

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Genotypes 4/16- 2/16- 1/16- RatioPhenotypes 9 3 3 1 Dihybrid Cross Template Cross: Foil:

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Genotypes 4/16- 2/16- 1/16- RatioPhenotypes 9 3 3 1 Dihybrid Cross Template Cross: Foil: