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Genetics

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Genetics

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    3. How can we figure it out? The Punnett Square Reginald Punnett (1875-1967) Basic principles of heredity Sex linkage Sex determination A Punnett square is a chart which shows/predicts all possible gene combinations in a cross of parents (whose genes are known). Punnett squares are named for an English geneticist, Reginald Punnett. He discovered some basic principles of genetics, including sex linkage and sex determination. He worked with the feather color traits of chickens in order to quickly separate male and female chickens. A Punnett square is a chart which shows/predicts all possible gene combinations in a cross of parents (whose genes are known). Punnett squares are named for an English geneticist, Reginald Punnett. He discovered some basic principles of genetics, including sex linkage and sex determination. He worked with the feather color traits of chickens in order to quickly separate male and female chickens.

    4. In pea plants, tall pea plants are dominant over short pea plants. Using a Punnett Square, we can predict the genotypes and phenotypes of the offspring The parents are a homozygous tall pea plant and a homozygous short pea plant.

    5. Designate the traits Capital letters = dominant traits Lowercase letters = recessive traits. ALWAYS use the same letter.

    6. Parent number one Our detail tells us – homozygous dominant TT Parent number two Our detail tells us homozygous recessive tt Cross them – TT X tt

    7. Who is giving up the genes? Parent one only has ‘T’ to offer Parent two only has ‘t’ to offer

    8. Draw a Punnett square Write the gene(s) of one parent across the top (TT) Write the gene(s) of the other parent along the side (tt)

    9. Fill in each box Transfer the letter above each column down Transfer the letter in front of each row across. Note: the capital letter goes first and a lowercase letter follows

    10. Genotype is now in the boxes. Genotype probability can be written as fractions or percents. Here all plants will be tall because the genotype is heterozygous Each offspring has a 4/4 or 100% chance of the Tt genotype.

    11. Now write the phenotype (physical appearance) in each box under the genotype. T = tall and t = short. Each of the offspring has a 4/4 or 100% chance of being tall.

    12. What are the possible genotype(s) of a tall plant? What are the possible genotype(s) of a short plant? What would be the phenotype of TT? What would be the phenotype of tt? Why is the phenotype of Tt tall and not medium/average?

    14. Bibliography http://www.usoe.k12.ut.us/curr/science/sciber00/7th/genetics/sciber/punnett.htm Vocabulary Practice http://school.discoveryeducation.com/teachingtools/worksheetgenerator/archive/952391162.html Try this website for practice: http://www.athro.com/evo/gen/punexam.html

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