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Jan 19, 2026

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3 pages

Understanding Genetics: Basic Terms and Punnett Squares

Yujun Ge

@yujunge_vslm

Genetics becomes less mysterious once you understand how traits are... Show more

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# Mendel's Method

Step 1

* Produced a "true-breeding" population called the "P" generation by self-pollinating
plants with the desir

Mendel's Method & Basic Genetic Concepts

Mendel's experimental approach was brilliantly simple yet effective. He first created "true-breeding" plants (the "P" generation) through self-pollination to ensure genetic purity. Next, he cross-pollinated these plants to produce the "F1" generation, and finally allowed the F1 plants to self-pollinate, creating the "F2" generation. His famous purple and white flower experiment revealed a 3:1 ratio in the F2 generation—a pattern that would become foundational to genetics.

When studying genetics, you'll encounter several key terms. An allele is simply one version of a gene $like you might have a brown-eye allele from mom and a blue-eye allele from dad$ . Everyone has two alleles for each trait, and we pass one of these to our offspring. Dominant alleles (written with capital letters) show themselves even when paired with a different allele, while recessive alleles (lowercase letters) only show when two copies are present.

The difference between phenotype (what you can observe—like blue eyes) and genotype (the actual genetic code—like "Bb") is crucial for understanding inheritance patterns. Genotypes can be either homozygous (two identical alleles, like BB or bb) or heterozygous (different alleles, like Bb).

💡 Think of dominance like this: if a dominant trait is like a loud speaker and a recessive trait is like a whisper, you'll only hear the whisper when there's no loud speaker present!

Monohybrid Crosses & Punnett Squares

A monohybrid cross follows just one trait through generations, making it easier to understand inheritance patterns. To predict the outcomes of such crosses, geneticists use Punnett squares—simple diagrams that help visualize possible combinations of alleles from each parent.

Creating a Punnett square is straightforward: first, determine what possible genetic contributions (gametes) each parent can make. Then place one parent's gametes across the top and the other's along the left side. Finally, fill in each box with the combined alleles. The resulting diagram shows both the genotypic ratio (the proportion of different genetic combinations) and the phenotypic ratio (the proportion of observable traits).

When you're trying to determine an unknown genotype, you can perform a test cross. This involves breeding the unknown individual with one that has a homozygous recessive genotype. If all offspring show the dominant trait, your unknown specimen is probably homozygous dominant. However, if some offspring show the recessive trait, the unknown parent must be heterozygous.

🔍 Punnett squares are like genetic calculators! They might seem tedious at first, but they'll soon become your go-to tool for predicting inheritance patterns on tests.

Test Cross Applications

Test crosses are powerful tools in genetics that help identify mystery genotypes. When you cross an organism showing a dominant trait (which could be either homozygous dominant or heterozygous) with a homozygous recessive individual, the results reveal the unknown genotype.

The key to interpreting test cross results is in the offspring patterns. If 100% of the offspring display the dominant trait, the unknown parent is likely homozygous dominant. But if any offspring shows the recessive trait, you can confidently determine that the unknown parent is heterozygous.

🧪 Think of a test cross as genetic detective work! By choosing the right "interrogation partner" (the homozygous recessive), you can get your mystery organism to reveal its genetic secrets.

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Jan 19, 2026

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3 pages

Understanding Genetics: Basic Terms and Punnett Squares

Yujun Ge

@yujunge_vslm

Genetics becomes less mysterious once you understand how traits are passed from generation to generation. Gregor Mendel, often called the "Father of Genetics," developed methods that revealed the patterns of inheritance we still use today to understand everything from eye... Show more

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Mendel's Method & Basic Genetic Concepts

💡 Think of dominance like this: if a dominant trait is like a loud speaker and a recessive trait is like a whisper, you'll only hear the whisper when there's no loud speaker present!

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Monohybrid Crosses & Punnett Squares

🔍 Punnett squares are like genetic calculators! They might seem tedious at first, but they'll soon become your go-to tool for predicting inheritance patterns on tests.

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Test Cross Applications

🧪 Think of a test cross as genetic detective work! By choosing the right "interrogation partner" (the homozygous recessive), you can get your mystery organism to reveal its genetic secrets.