#AP Biology Unit 5: Heredity - The Ultimate Study Guide

Hey there, future AP Bio superstar! Let's dive into Unit 5, where we explore the fascinating world of heredity. This guide is designed to be your go-to resource for a quick, effective review. Let's make sure you're feeling confident and ready to ace that exam! 🚀

#5.1 Meiosis: The Foundation of Genetic Diversity

#What is Heredity?

• Heredity is simply the passing of genes from parents to offspring. Think of it as your family's biological legacy! 🧬
• This process begins with meiosis, a special type of cell division that creates gametes (sperm and egg cells).

* **Genetics** is the scientific study of heredity and how traits are passed down.

#Meiosis vs. Mitosis

• Meiosis is all about creating genetic variation. It's like shuffling a deck of cards to get a unique hand every time.
• It involves one round of DNA replication followed by two rounds of cell division.
• The result? Four genetically unique, haploid cells (gametes) – each with half the genetic material of a normal diploid cell.

Caption: A visual overview of the two stages of meiosis, highlighting the reduction in chromosome number and the generation of genetic diversity.

#5.2 Meiosis and Genetic Diversity: The Remix

#Three Ways Meiosis Creates Variation

1. Crossing Over: During meiosis, homologous chromosomes exchange bits of DNA. It's like swapping puzzle pieces to create new combinations. 🧩
2. Independent Assortment: Chromosomes line up randomly during meiosis, mixing up maternal and paternal chromosomes. Imagine shuffling two decks of cards together – that's independent assortment! 🔀
3. Random Fertilization: The chance union of any sperm and egg further increases variation. It's a lottery with trillions of possible outcomes! 🎰

#5.3 Mendelian Genetics: The OG Rules of Inheritance

#Gregor Mendel's Legacy

• Gregor Mendel is the father of genetics! He discovered basic inheritance patterns using pea plants. 🪴
• He focused on dominant and recessive alleles, where one allele masks the effect of the other.
• The dominant allele usually determines the phenotype (physical trait).

#Mendel's Laws

1. Law of Dominance: In a heterozygote, the dominant allele will express its trait.
2. Law of Segregation: During gamete formation, allele pairs separate so each gamete only gets one allele.
3. Law of Independent Assortment: Alleles of different genes assort independently of one another during gamete formation.

#5.4 Non-Mendelian Genetics: When Things Get Complicated

#Beyond Simple Dominance

• Multiple Alleles: More than two alleles exist for a trait (e.g., rabbit fur color).
• Incomplete Dominance: Neither allele is fully dominant, resulting in a blended phenotype (e.g., pink flowers from red and white parents). 🌸
• Co-dominance: Both alleles are expressed equally (e.g., spotted cows with both white and brown patches). 🐄
• Sex-Linked Traits: Traits located on sex chromosomes (usually the X chromosome). Men are more likely to express recessive sex-linked traits because they only have one X chromosome (e.g., color blindness).

#5.5 Environmental Effects on Phenotype: Nature vs. Nurture

#The Influence of the Environment

• The environment can impact which traits become more common in a population.
• If a phenotype gives an individual a survival or reproductive advantage, that trait will likely increase in the population.

#5.6 Chromosomal Inheritance: Predicting the Future

#Punnett Squares

• Punnett squares are used to predict the probability of offspring genotypes and phenotypes. It's like a game of chance with genes! 🎲
• Chromosomes are organized structures that make DNA distribution during cell division easier.

Caption: A simple Punnett square demonstrating the inheritance pattern of a dominant green allele.

#Key Terms: Your Genetic Glossary

• Meiosis: Cell division that produces gametes.
• Diploid: Having two sets of chromosomes.
• Haploid: Having one set of chromosomes.
• Gamete: Sex cell (sperm or egg).
• Chromosome: Structure containing DNA.
• Homologous Chromosome: Paired chromosomes with genes for the same traits.
• Sister Chromatid: Identical copies of a chromosome.
• Genetic Variation: Differences in genetic material.
• Crossing Over: Exchange of DNA between homologous chromosomes.
• Random Fertilization: Chance union of sperm and egg.
• Independent Assortment: Random alignment of chromosomes during meiosis.
• Zygote: Fertilized egg cell.
• Law of Segregation: Allele pairs separate during gamete formation.
• Laws of Probability: Rules governing the likelihood of events.
• Genotype: Genetic makeup of an organism.
• Phenotype: Physical traits of an organism.
• Allele: Different forms of a gene.
• Gene: Unit of heredity.
• Sex-linked: Gene located on a sex chromosome.
• Pedigree: Family tree showing inheritance patterns.
• Nondisjunction: Failure of chromosomes to separate properly during meiosis.
• Mutation: Change in DNA sequence.
• Mitochondria: Organelle with its own DNA.
• Chloroplast: Organelle with its own DNA (in plants).

#Final Exam Focus: What to Prioritize

#High-Priority Topics

• Meiosis: Understand the steps and how it creates variation.
• Mendelian and Non-Mendelian Genetics: Be able to solve genetics problems using Punnett squares and understand the different inheritance patterns.
• Genetic Variation: Know the mechanisms that generate diversity.

#Common Question Types

• Multiple Choice Questions: Often test your understanding of key terms and concepts, as well as your ability to apply genetics principles.
• Free Response Questions (FRQs): May ask you to analyze genetic crosses, interpret data, or explain the significance of meiosis and genetic variation.

#Last-Minute Tips

• Time Management: Don't spend too long on any one question. If you're stuck, move on and come back later.
• Read Carefully: Pay close attention to the wording of each question.
• Show Your Work: Even if you make a mistake, you can still earn partial credit for showing your thought process.
• Stay Calm: You've got this! Take a deep breath and trust your preparation. 🧘

#Practice Questions

Practice Question

#Multiple Choice Questions

1. In a certain species of plant, the allele for purple flowers (P) is dominant over the allele for white flowers (p). If two heterozygous plants are crossed, what percentage of the offspring would be expected to have white flowers? (A) 0% (B) 25% (C) 50% (D) 75%

2. Which of the following processes contributes most directly to genetic variation in a population? (A) Mitosis (B) Binary fission (C) Meiosis (D) Asexual reproduction

3. A man with type AB blood marries a woman with type O blood. What are the possible blood types of their children? (A) A, B, and O (B) A and B only (C) AB only (D) O only

#Free Response Question

Scenario: In fruit flies, gray body color (G) is dominant to ebony body color (g), and long wings (L) are dominant to vestigial wings (l). A cross was made between a heterozygous gray, long-winged fly (GgLl) and an ebony, vestigial-winged fly (ggll).

(a) What are the genotypes of the gametes produced by each parent? (2 points) (b) Using a Punnett square, determine the expected phenotypic ratio of the offspring. (3 points) (c) Explain how the process of independent assortment contributes to the genetic variation observed in the offspring. (2 points) (d) If a test cross was performed with a gray, long-winged fly of unknown genotype and an ebony, vestigial-winged fly, and the offspring showed a 1:1 phenotypic ratio of gray, long-winged to ebony, vestigial-winged flies, what is the genotype of the unknown parent? (2 points)

Scoring Breakdown:

(a)

• Parent 1 (GgLl) gametes: GL, Gl, gL, gl (1 point)
• Parent 2 (ggll) gametes: gl (1 point)

(b)

• Correct Punnett square setup (1 point)
• Correct genotypes of offspring (1 point)
• Phenotypic ratio: 1 gray, long-winged : 1 ebony, vestigial-winged (1 point)

(c)

• Independent assortment: alleles of different genes assort independently during gamete formation (1 point)
• This creates new combinations of alleles in the offspring, increasing genetic variation (1 point)

(d)

• Genotype of unknown parent: Ggll (2 points)

Alright, you've got this! Go ace that exam! 🎉