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Question
analysis questions:
- how do punnett squares assist in predicting traits in offspring?
- describe the steps needed to create a punnett square.
- from the completed punnett square in the example, what is the probability of producing a tall plant?
- explain the significance of using pedigrees in genetics.
- what does a filled-in shape in a pedigree chart indicate? what do you think a half - filled in shape would indicate?
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Question 1
Punnett Squares use parental genotypes to show all possible allele combinations in offspring. By listing gametes of each parent (one along top, one along side), then combining them in the squares, we can see the probability of each genotype (and thus phenotype) in the offspring. This helps predict the likelihood of traits being passed on, as it visualizes Mendelian inheritance (dominant/recessive, etc.) and the chance of each genetic outcome.
- Identify Parental Genotypes: Determine the alleles (e.g., for height, \( T \) = tall, \( t \) = short) of each parent.
- List Gametes: For each parent, figure out the possible gametes (allele combinations) they can produce. If a parent is \( Tt \), gametes are \( T \) and \( t \); if \( TT \), only \( T \).
- Set Up the Square: Draw a grid (e.g., 2x2 for a monohybrid cross). Place one parent’s gametes along the top, the other’s along the left side.
- Fill the Square: Combine the allele from the top (column) and left (row) for each square to get the offspring’s genotype.
- Analyze Genotypes/Phenotypes: Count the number of each genotype (and corresponding phenotype) to find ratios/probabilities.
Step 1: Recall the Punnett Square Setup
If the cross is \( Tt \times Tt \), the Punnett Square would have gametes \( T, t \) (top) and \( T, t \) (left). Filling the square gives genotypes: \( TT \) (top-left), \( Tt \) (top-right), \( Tt \) (bottom-left), \( tt \) (bottom-right).
Step 2: Determine Phenotypes
- \( TT \) and \( Tt \) = tall (dominant allele present).
- \( tt \) = short.
Step 3: Calculate Probability
Total offspring genotypes: 4. Tall genotypes: \( TT, Tt, Tt \) (3 out of 4). So probability = \( \frac{3}{4} \) (75%).
(If the example is \( TT \times tt \), all offspring are \( Tt \) (tall), so probability = 100% (\( \frac{4}{4} \)).)
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Punnett Squares list parental gametes (allele combinations) along the top/side, then combine them in squares to show all possible offspring genotypes. By calculating the ratio of genotypes (and corresponding phenotypes) in the squares, we predict the probability of traits in offspring, using Mendelian inheritance principles (e.g., dominant/recessive allele interactions) to interpret the phenotypic likelihood.