Genetics and Punnett Squares Explained

Understanding How Traits Pass from Parents to Offspring Grade 5 Science 60 Minutes

Think About This...

Why do mountain lions have different fur colors? What makes you look like your parents? How do traits get passed down?

Genetics Vocabulary

Gene: A unit of heredity that carries information from parent to offspring Allele: Different forms of the same gene Dominant allele: An allele that masks another (shown with capital letter) Recessive allele: An allele that is masked by the dominant (shown with lowercase letter)

Dominant vs. Recessive Traits

{"left":"Dominant Traits\nShow up even with just ONE copy\nMask recessive traits\nWritten with CAPITAL letters (B)\nExample: Brown fur in mountain lions","right":"Recessive Traits\nNeed TWO copies to show up\nHidden by dominant traits\nWritten with lowercase letters (b)\nExample: Tan fur in mountain lions"}

What is a Punnett Square?

A chart that helps predict traits in offspring Shows all possible combinations of alleles Helps calculate probability of traits Named after scientist Reginald Punnett

Mountain Lion Punnett Square Example

Your Turn: Practice Time!

Work with a partner Complete 3 different Punnett squares: 1. Bb × Bb (both brown fur) 2. Bb × bb (brown × tan) 3. bb × bb (both tan) Use your trait cards and grid sheets

Let's Check Our Answers!

Cross 1 (Bb × Bb): 75% brown, 25% tan Cross 2 (Bb × bb): 50% brown, 50% tan Cross 3 (bb × bb): 0% brown, 100% tan Notice how percentages change with different parents!

Quick Assessment Quiz

1. What does a dominant allele do? 2. Complete this Punnett square: Bb × Bb 3. If two tan mountain lions (bb × bb) have babies, what color will the babies be? 4. Why might brown-furred parents have a tan-furred baby?

What We Learned Today

Genes carry traits from parents to offspring Dominant alleles mask recessive alleles Punnett squares predict possible traits Mountain lions can have brown or tan fur Coming up next: How environment affects traits!