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Backcross Breeding

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Backcross Breeding 1 - Basic Gene Inheritance

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Summary - Basic Gene Inheritance

Homozygous: 2 copies of the same allele. (AA)
Heterozygous: 1 copy each of 2 different alleles. (Aa)
Hemizygous: 1 copy of a gene with no alternate allele or gene on the other chromosome. (A_)
Dominant alleles mask the expression of recessive alleles.
IF A = dominant for tall trait
AND a = recessive for short trait
THEN
AA = tall plant
Aa = tall plant
aa = short plant
A Punnett square is used to predict the ratios of the offspring genotypes and phenotypes.
To determine if a plant is homozgous or heterzygous for a dominant trait, self-pollinate the plant, plant the seed in progeny rows and observe the offspring phenotypes and their ratios. Homozygous plants will be truebreeding with all offspring expressing the trait. Heterozygous plants will have mixed offspring.

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This project was supported in part by the National Research Initiative Competitive Grants CAP project 2011-68002-30029 from the USDA National Institute of Food and Agriculture, adminstered by the University of California-Davis and by the National Science Foundation (NSF), Division of Undergraduate Education, National SMETE Digital Library Program, Award #0938034, administered by the University of Nebraska. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the USDA or NSF.