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What Is a Genotype? — Reading Comprehension

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MS-LS3-1
MS-LS3-2

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This NGSS-aligned reading passage introduces the concept of genotype for middle school students. It defines genotype as the genetic makeup of an organism, explains how dominant and recessive alleles work, and distinguishes between genotype and phenotype. Students learn how Punnett squares are used to predict offspring traits and how siblings can inherit different genotypes. The passage also explores the real-life importance of genotypes in medicine and agriculture. Clear definitions and real-world examples support reading comprehension and science learning under NGSS standard MS-LS3-1 (Heredity: Inheritance and Variation of Traits).

CONTENT PREVIEW

In genetics, a genotype is the set of genes that an organism carries. It is made up of alleles, which are different versions of a gene. These alleles are inherited from an organism’s parents—one from the mother and one from the father. The genotype determines the potential traits an organism may have, even if some traits are not visible on the outside.

Each gene usually comes in at least two forms: a dominant allele and a recessive allele. The combination of these alleles makes up the genotype. For example, a person might have a BB, Bb, or bb genotype for eye color. BB and Bb genotypes would both show the dominant trait, such as brown eyes, while bb would show the recessive trait, like blue eyes.

Even though two organisms may look the same on the outside, their genotypes can be different. This is because the genotype includes both dominant and recessive alleles, even if the recessive allele doesn't affect appearance. This difference between what you see (called the phenotype) and the genes inside (the genotype) is important in understanding how traits are passed down.

Scientists use Punnett squares to predict possible genotypes of offspring. This helps explain why siblings from the same parents can look different—they inherit different combinations of alleles.

In medicine, knowing a person’s genotype can help doctors understand their risk for certain diseases, and in agriculture, breeders use genotype knowledge to grow crops with desired traits. The study of genotypes helps us better understand heredity, genetic variation, and even evolution.

Fun Fact: You share about 99.9% of your genotype with every other human being—but that tiny 0.1% is what makes you unique!

What is a genotype?

A visible traitA type of mutationThe set of genes an organism hasA part of the phenotype

What are alleles?

Cells in the bloodDifferent versions of a geneTraits passed to friendsMuscles in the body

Which genotype will express a recessive trait?

BBBbbBbb

What tool is used to predict genotypes?

MicroscopeDNA chartPunnett squareGene spinner

How can two organisms look the same but have different genotypes?

They have the same phenotype but different allelesOne is mutatedThey have no allelesAll genes are dominant

Why can siblings look different from each other?

They share no allelesThey inherit different combinations of allelesOne sibling changes their genesThey don’t share traits

What is the main idea of the passage?

Phenotypes are more important than genotypesGenotypes control visible traits onlyGenotypes are gene combinations that affect traitsPunnett squares are hard to use

How is genotype knowledge useful in real life?

It helps in planting treesIt reduces water useIt helps predict traits and disease riskIt improves human height