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Unit Review - Heredity: Inheritance and Variation

Grade 7 Science Unit Review

📚 Science 🎓 Grade 7 ⏱️ 45 minutes

Learning Objectives

  • Distinguish between inherited and acquired traits and explain the relationship between DNA, chromosomes, and genes

  • Define alleles, distinguish dominant from recessive, and explain the difference between genotype and phenotype

  • Use Punnett squares to predict offspring trait probabilities

  • Compare sexual and asexual reproduction and explain why genetic variation is important for species survival

  • Describe how environment and lifestyle can affect gene expression and distinguish heritable mutations from non-heritable changes

Progress 7 sections
1

Introduction

~1 minutes

Unit Review: Heredity - Inheritance and Variation

This review covers everything we learned about genetics and heredity. Use it to prepare for your unit assessment.

2

Review: Heredity, Traits, and Genes

~5 minutes

Topic 1: Heredity, Traits, and Genes

Heredity is the passing of traits from parents to offspring through genetic information.

Two Types of Traits:
• Inherited traits: Determined by genes, passed from parents (eye color, blood type, tongue rolling). CAN be passed to offspring.
• Acquired traits: Develop during life through environment or choices (scars, muscles from exercise, learned skills). CANNOT be passed to offspring.

The Genetic Hierarchy (smallest → largest):
• Gene → segment of DNA with instructions for a trait (~20,000-25,000 in humans)
• Chromosome → organized structures of DNA (46 in humans, 23 pairs, 23 from each parent)
• Nucleus → cell's control center containing chromosomes
• Cell → fundamental unit of life

DNA is a double-helix molecule, a twisted ladder whose rungs spell out genetic instructions.

3

Review: Alleles, Genotype, and Phenotype

~5 minutes

Topic 2: Alleles, Genotype, and Phenotype

Alleles are different versions of the same gene. You have two alleles for each gene, one from each parent.

- Dominant allele (CAPITAL letter, B): Only needs ONE copy to show the trait
• Recessive allele (lowercase, b): Needs TWO copies to show the trait

Genotype = the actual alleles (BB, Bb, or bb) Phenotype = the observable trait (what you see)

GenotypeNamePhenotype
BBHomozygous dominantDominant trait shows
BbHeterozygousDominant trait shows
bbHomozygous recessiveRecessive trait shows
Homozygous = same alleles (AA or aa). Heterozygous = different alleles (Aa).

4

Review: Punnett Squares

~4 minutes

Topic 3: Punnett Squares

A Punnett square is a grid that shows all possible offspring genotypes from two parents.

Key Crosses to Know:
• BB × bb → 100% Bb → 100% dominant phenotype
• Bb × Bb → 25% BB : 50% Bb : 25% bb → 75% dominant : 25% recessive
• Bb × bb → 50% Bb : 50% bb → 50% dominant : 50% recessive
• bb × bb → 100% bb → 100% recessive

Important: Punnett squares show probability, not certainty. Each offspring's outcome is determined independently, like flipping a coin.

5

Review: Reproduction and Genetic Variation

~5 minutes

Topic 4: Reproduction and Genetic Variation

Sexual Reproduction: Two parents → unique offspring → HIGH genetic variation Asexual Reproduction: One parent → clones (identical) → LOW genetic variation

Methods of Asexual Reproduction:
• Binary fission (bacteria split)
• Budding (yeast)
• Fragmentation (starfish)
• Vegetative propagation (strawberry runners, onion bulbs)

Why Genetic Variation Matters:
• Provides raw material for natural selection
• Some individuals may survive diseases others can't
• Allows species to adapt to change
• Acts as 'insurance' against threats

The Banana Warning: All Cavendish bananas are clones, so no genetic variation means no resistance to Panama Disease (TR4).

6

Review: Environment and Inheritance

~3 minutes

Topic 5: Environment, Lifestyle, and Inheritance

Three ways environment matters: 1. Changes gene expression - sunlight increases melanin, exercise activates muscle genes (DNA NOT changed) 2. Can cause mutations - UV or chemicals damage DNA - Body cell (somatic) mutation → NOT inherited - Egg or sperm (germ cell) mutation → CAN be inherited 3. Changes survival outcomes - same trait can be helpful or harmful depending on environment

Key examples:
• PKU: inherited gene, but diet reduces harmful effects
• Sickle cell: one allele helps in malaria regions

Remember: Most lifetime changes (muscles, scars, tans, skills) are NOT inherited.

7

Unit Assessment

~22 minutes
Question 1

Which is the BEST definition of heredity?

Question 2

Which of the following is an INHERITED trait?

Question 3

Maria has naturally curly hair. She straightens it every day with a flat iron. If Maria has children, what type of hair will they most likely inherit?

Question 4

How many chromosomes does a typical human body cell contain?

Question 5

Match each term with its correct definition:

Question 6

Arrange the following from SMALLEST to LARGEST:

[Unsupported question type: ordering]

Question 7

What is an allele?

Question 8

For a recessive trait to appear in an organism's phenotype, the organism must:

Question 9

Two organisms have the same phenotype (brown fur) but different genotypes (BB and Bb). Why do they look the same?

Question 10

Match each genotype to its correct name:

Question 11

Classify each trait as INHERITED or ACQUIRED:

Question 12

A Punnett square cross between two Bb parents produces what genotype ratio?

Question 13

What is the PHENOTYPE ratio when two Bb parents are crossed? (B = brown fur, b = white fur)

Question 14

A BB parent is crossed with a bb parent. What percentage of offspring will show the DOMINANT trait?

Question 15

A mother cannot roll her tongue (rr) and a father can roll his tongue (Rr). What is the probability their child will be able to roll their tongue?

Question 16

Match each Punnett square cross to its phenotype outcome (B = dominant brown, b = recessive white):

Question 17

What BEST describes the difference between sexual and asexual reproduction?

Question 18

Sexual reproduction usually creates more genetic variation among offspring than asexual reproduction.

Question 19

Why does sexual reproduction create more genetic variation than asexual reproduction?

Question 20

All Cavendish bananas are clones. Why does this make them vulnerable to Panama Disease?

Question 21

Match each method of asexual reproduction with its description:

Question 22

Why is genetic variation important for species survival? (Select ALL that apply)

Select all that apply.

Question 23

Put these events in order when a new disease threatens a population WITH genetic variation:

[Unsupported question type: ordering]

Question 24

Which statement best describes gene expression?

Question 25

Which situations could cause a DNA change that might be INHERITED by offspring? (Select all that apply)

Select all that apply.

Question 26

PKU is a good example of how environment affects an inherited condition because:

Question 27

When bacteria reproduce by binary fission, the two new cells are genetically different from each other.

Question 28

Where are genes located in a cell?

Question 29

Why can inbreeding increase the risk of genetic disorders?

Question 30

How does approximately 2 meters of DNA fit inside a tiny cell nucleus?