Decoding Family Trees: Understanding Pedigrees in Genetics

Biology Grades High School 6:08 Video
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Lesson Description

Learn how to read and analyze pedigrees to understand inheritance patterns of traits within families. This lesson covers pedigree symbols, autosomal dominant traits, and genotype/phenotype relationships.

Video Resource

Pedigrees | Classical genetics | High school biology | Khan Academy

Khan Academy

Duration: 6:08
Watch on YouTube

Key Concepts

  • Pedigree symbols and their meanings (circles, squares, shaded/unshaded)
  • Marriage/coupling lines and lines of descent
  • Autosomal dominant inheritance
  • Genotype vs. Phenotype
  • Alleles and their role in trait expression

Learning Objectives

  • Students will be able to correctly identify and interpret the symbols used in pedigrees.
  • Students will be able to distinguish between genotype and phenotype.
  • Students will be able to analyze pedigrees to determine the mode of inheritance (specifically autosomal dominant).
  • Students will be able to infer possible genotypes of individuals within a pedigree based on their phenotype and family history.

Educator Instructions

  • Introduction (5 mins)
    Begin by asking students if they have ever seen a family tree. Explain that a pedigree is a type of family tree used in genetics to track traits. Briefly introduce the concept of inheritance.
  • Video Viewing (10 mins)
    Play the Khan Academy video "Pedigrees | Classical genetics | High school biology | Khan Academy." Instruct students to take notes on the key vocabulary and concepts presented.
  • Symbol Breakdown and Note Taking (10 mins)
    After the video, review the pedigree symbols: circles (females), squares (males), shaded (affected), unshaded (unaffected), marriage lines, and lines of descent. Have students create their own key for pedigree symbols in their notebooks.
  • Autosomal Dominant Explanation (10 mins)
    Explain autosomal dominant inheritance in detail, including the concepts of alleles (dominant and recessive), homozygous dominant, heterozygous, and homozygous recessive genotypes. Use the freckles example from the video. Explain that only one dominant allele is needed for an individual to express the trait.
  • Practice Problem and Analysis (10 mins)
    Present students with a sample pedigree (either pre-made or draw one on the board). Guide them through analyzing the pedigree to determine the possible genotypes of individuals based on their phenotypes and family history. Start with an easy example and increase complexity.
  • Wrap-up and Q&A (5 mins)
    Summarize the main points of the lesson. Answer any remaining student questions. Preview the next lesson on other inheritance patterns (e.g., autosomal recessive, X-linked).

Interactive Exercises

  • Build-a-Pedigree
    Provide students with a scenario describing a family with a particular trait. Have them work in small groups to construct a pedigree representing the family history.
  • Genotype Inference Challenge
    Present students with partially completed pedigrees. Challenge them to infer the missing genotypes of individuals based on the information provided.

Discussion Questions

  • Why are pedigrees useful tools in genetics?
  • How can you tell if a trait is dominant or recessive by looking at a pedigree?
  • What are some limitations of using pedigrees to study inheritance?
  • Can you think of any ethical considerations related to using genetic information obtained from pedigrees?

Skills Developed

  • Data analysis and interpretation
  • Critical thinking and problem-solving
  • Scientific communication
  • Visual representation of data

Multiple Choice Questions

Question 1:

In a pedigree, what does a shaded circle represent?

Correct Answer: An affected female

Question 2:

What does a horizontal line connecting a male and female in a pedigree represent?

Correct Answer: A marriage or reproductive relationship

Question 3:

What is the term for the observable characteristics of an individual?

Correct Answer: Phenotype

Question 4:

In an autosomal dominant trait, what genotype(s) will express the trait?

Correct Answer: Both homozygous dominant (FF) and heterozygous (Ff)

Question 5:

What does 'autosomal' mean in the context of genetics?

Correct Answer: Related to non-sex chromosomes

Question 6:

If both parents are heterozygous (Ff) for an autosomal dominant trait, what is the probability that their child will NOT express the trait?

Correct Answer: 25%

Question 7:

A vertical line extending downward from a marriage line in a pedigree represents:

Correct Answer: Line of descent to offspring

Question 8:

Which of the following is NOT a standard symbol used in a pedigree?

Correct Answer: Diamond

Question 9:

What can pedigrees help us understand and predict?

Correct Answer: Past inheritance patterns and future inheritance probabilities

Question 10:

If an individual does not have a certain trait, what genotype(s) can be ruled out if the trait is autosomal dominant?

Correct Answer: Both FF and Ff

Fill in the Blank Questions

Question 1:

A _________ represents a male in a pedigree.

Correct Answer: square

Question 2:

The genetic makeup of an individual is called their _________.

Correct Answer: genotype

Question 3:

If a trait is _________ dominant, only one copy of the dominant allele is needed for the trait to be expressed.

Correct Answer: autosomal

Question 4:

Different versions of a gene are called _________.

Correct Answer: alleles

Question 5:

A line connecting parents to their offspring in a pedigree is called the line of _________.

Correct Answer: descent

Question 6:

An individual with two identical alleles for a trait is said to be _________ for that trait.

Correct Answer: homozygous

Question 7:

In a pedigree, a shaded symbol indicates that the individual __________ the trait.

Correct Answer: exhibits

Question 8:

Chromosomes that are not sex chromosomes are called _________.

Correct Answer: autosomes

Question 9:

A pedigree is a way of analyzing the __________ patterns of a trait within a family.

Correct Answer: inheritance

Question 10:

An individual with two different alleles for a trait is said to be _________ for that trait.

Correct Answer: heterozygous

Educational Standards

B.LS3.1:Ask questions to clarify relationships about the role of DNA and chromosomes in coding the instructions for characteristic traits passed from parents to offspring. B.LS3.3:Apply concepts of statistics and probability to explain the variation and distribution of expressed traits in a population.

Teaching Materials

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