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Punnett Squares
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Activating Question Define the term in yellow!
The Westlake basketball team dominated Pebble Brook High School last weekend.
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Mendelian Genetics In the mid-1800’s, a monk named Gregor Mendel studied how traits are passed down from one generation to the next using pea plants. He is now known as the “father of genetics.”
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Mendelian Genetics Do you remember? What are genes?
Where do we get them from?
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Mendelian Genetics Genes are parts of chromosomes that determine traits For instance genes tell us our hair color, eye color, height, etc. Genes can come in different varieties called alleles The gene for hair color can have brown, black, or blonde alleles. What are some alleles for eye color?
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Mendelian Genetics 2 1 We inherit ___ alleles for each gene: ___ from each parent. Those traits can either be dominant (capital letter) or recessive (lower case letter). Dominant or recessive allele? R q r T M a Y L Dominant Recessive Recessive Dominant Dominant Recessive Dominant Dominant
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Mendelian Genetics If the alleles we inherit are the same, we call them homozygous. i.e. AA, ff, JJ, LL, nn If the alleles we inherit are different, we call them heterozygous. i.e. Aa, Ff, Jj, Ll, Mm Homozygous (1 finger) or Heterozygous (2 fingers)? AA 5. Pp Mm 6. TT Nn 7. oo kk 8. Cc Homozygous Heterozygous Heterozygous Homozygous Heterozygous Homozygous Homozygous Heterozygous
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Mendelian Genetics If there is at least one dominant allele present for a gene, that allele will dominate and be expressed. Otherwise, the recessive allele will be expressed.
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Mendelian Genetics Dominant Recessive Dominant Dominant Dominant
Dominant or recessive? (Remember: Dominant alleles use CAPITAL letters) AA 4. ee 7. Hh Bb 5. Ff 8. hh CC 6. gg 9. ii If red flowers (R) are dominant to white flowers (r): What color would RR be? What color would rr be? What color would Rr be? Dominant Recessive Dominant Dominant Dominant Recessive Dominant Recessive Recessive Red White Red
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Mendelian Genetics The combination of alleles is called the genotype
i.e. RR, Rr, rr The trait that is shown is called the phenotype i.e. Red, White, Tall, Brown hair
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Mendelian Genetics When two alleles combine, there are different possibilities for which allele will be expressed (RR? Rr? rr?) We use a Punnett Square to show the options.
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Mendelian Genetics Guide for creating a Punnett Square
Draw a box and split it into four smaller boxes (2x2) Put the two alleles for one parent on the top over each box Put the two alleles for the other parent along the side next to each box In the boxes you put one allele from the top and one allele from the side
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Mendelian Genetics R r RR R Rr Rr rr r
Guide for creating a punnett square Rr x Rr R r RR R Rr Rr rr r
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Mendelian Genetics Let’s Practice
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AA ___ Ee___ Ii ____ Mm ____
Bb ___ ff ___ Jj ___ nn ___ Cc ___ GG ___ kk ___ OO ___ Dd ___ HH ___ Ll ___ Pp ___ HO HE HE HE HO HE HO HE HO HE HO HO HE HE HO HE
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2. PP ___________ BB _____________ Pp ___________ Bb _____________ pp ___________ bb _____________ RR ___________ SS _____________ Rr ___________ Ss _____________ Rr ____________ ss _____________ purple brown purple brown white blue round straight round straight wrinkled curly
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3. Rr x rr What percentage of the offspring will be round? Rr Rr 50% rr rr
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4. Rr x Rr What percentage of the offspring will be round? RR Rr 75% Rr rr
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