# What Makes You, You?

Look around your classroom. Every person you see is unique—different heights, different hair colors, different eye colors, different faces. Yet if you've ever met identical twins, you know that two people can look almost exactly alike. What explains both our differences AND our similarities?

The answer lies in heredity—the passing of traits from parents to their offspring. In this lesson, you'll discover how tiny molecules inside your cells carry instructions that help determine everything from your eye color to whether you can roll your tongue.

Essential Question: How do organisms pass traits to their offspring?

# Understanding Traits

## What is a Trait?

A trait is any characteristic of an organism that can be observed or measured. Traits include: - Physical features you can see (hair color, eye color, height) - Physiological characteristics (blood type, ability to digest lactose) - Behavioral tendencies (activity levels in some animals)

Traits can be organized into two major categories based on how they are acquired.

## Inherited Traits

Inherited traits are characteristics passed from parents to offspring through genetic information. You received half of your genetic information from your biological mother and half from your biological father. These traits were determined before you were born and cannot be changed by your environment or choices.

Examples of inherited traits: | Trait | Possible Variations | |-------|-------------------| | Natural hair color | Black, brown, blonde, red | | Hair texture | Straight, wavy, curly | | Eye color | Brown, blue, green, hazel | | Earlobe attachment | Attached or detached (free-hanging) | | Tongue rolling | Can roll into tube or cannot | | Widow's peak | V-shaped hairline or straight hairline | | Dimples | Present or absent | | Blood type | A, B, AB, or O |

## Acquired Traits

Acquired traits are characteristics that develop during an organism's lifetime due to environment, experiences, learning, or choices. These traits are NOT passed to offspring because they do not change the organism's genetic information.

Examples of acquired traits: - Scars from injuries - Muscles developed from exercise - Knowledge and skills learned in school - Language(s) you speak - Dyed hair color - Tattoos or piercings - A suntan - Playing a musical instrument - Fears or phobias developed from experiences

# From DNA to Traits: The Genetic Blueprint

## The Building Blocks of Heredity

Inside nearly every cell of your body is a control center called the nucleus. Within the nucleus are long, thread-like structures called chromosomes. Humans have 46 chromosomes arranged in 23 pairs—you inherited 23 chromosomes from your mother and 23 from your father.

Chromosomes are made of an amazing molecule called DNA (deoxyribonucleic acid). DNA looks like a twisted ladder—scientists call this shape a double helix. The 'rungs' of this ladder are made of chemical bases that spell out instructions, like letters in an instruction manual.

## The Genetic Hierarchy

Think of it like a library: - DNA = The entire library (all genetic information) - Chromosomes = Individual books in the library (46 in humans) - Genes = Chapters or recipes in each book (~20,000-25,000 total in humans) - Traits = The finished products those recipes create

## How Genes Work

When a cell needs to perform a specific function—like making the pigment that colors your eyes—it reads the appropriate gene and follows its instructions to build the necessary protein.

Important facts about genes: - You have TWO copies of every gene (one from mom, one from dad) - Your unique combination makes you different from everyone else - Siblings share parents but receive different gene combinations - Only identical twins have the exact same genes

This explains why you might have your mother's eye color but your father's hair texture, or your grandmother's nose shape.

# Traits in Families

## The Martinez Family: A Case Study

Let's examine how traits pass through a family:

Parents: - Maria Martinez: Brown eyes, curly hair, attached earlobes, can roll tongue, has dimples - Carlos Martinez: Brown eyes, straight hair, detached earlobes, cannot roll tongue, no dimples

Children: - Sofia (age 14): Brown eyes, wavy hair, detached earlobes, can roll tongue, has dimples - Miguel (age 11): Brown eyes, curly hair, attached earlobes, cannot roll tongue, no dimples

Observations: - Both children have brown eyes like both parents - Sofia has wavy hair (a blend between curly and straight) - Miguel has curly hair like his mother - Each child received different combinations of traits - Neither child is identical to either parent

## Observable Human Traits

Here are several inherited traits you can easily observe in yourself and others:

| Trait | Variation 1 | Variation 2 | |-------|-------------|-------------| | Earlobes | Attached (connected to head) | Detached (free-hanging) | | Tongue Rolling | Can roll into tube shape | Cannot roll | | Hairline | Widow's peak (V-shape) | Straight hairline | | Dimples | Present when smiling | Absent | | Freckles | Present | Absent | | Hand Clasping | Left thumb naturally on top | Right thumb naturally on top | | Cleft Chin | Present (dimple in chin) | Absent |

These variations exist because different versions of genes produce different results. In Lesson 2, you'll learn that these different versions are called alleles.

# Summary

## Key Concepts Review

Heredity is the process by which traits are passed from parents to offspring through genetic information.

Traits are observable characteristics that come in two types: - Inherited traits: Determined by genes, passed from parents (eye color, blood type, natural hair color) - Acquired traits: Develop during life, NOT passed to offspring (scars, learned skills, dyed hair)

The Genetic Hierarchy: - DNA: Double helix molecule containing all genetic instructions - Chromosomes: Organized structures of DNA (46 in humans, in 23 pairs) - Genes: Specific segments of DNA controlling specific traits (~20,000-25,000 in humans)

Why Family Members Are Similar But Not Identical: - Each person receives 50% of genes from each biological parent - The random combination creates unique individuals - Siblings share parents but receive different gene combinations - Only identical twins have the same genetic makeup