#AP Biology: Genetics & Heredity - The Night Before 🧬

Hey! Let's get you feeling confident and ready for your AP Biology exam. We're going to break down genetics and heredity into bite-sized pieces, focusing on what's really important. Let's do this!

#Genetic Variation: The Spice of Life

#The Foundation of Diversity

• Independent Assortment: During meiosis, genes for different traits are sorted into gametes independently of each other. This means that the inheritance of one trait doesn't affect the inheritance of another. Think of it like shuffling two decks of cards separately – you get a ton of unique combinations.

• Random Fertilization: It's totally random which sperm fertilizes which egg. This adds another layer of variation to the mix. It's like a lottery – each combination is unique!

• Crossing Over: During meiosis I, homologous chromosomes swap genetic material. This process, called crossing over, creates new combinations of alleles on the same chromosome, increasing genetic diversity.

#Why Meiosis Matters

• Mitosis vs. Meiosis: Remember, we don't do mitosis for reproduction because that would create clones! Meiosis ensures genetic variation, which is crucial for a population's survival against diseases and environmental changes. It's all about that survival advantage! 💪

#Punnett Squares: Predicting the Future (Sort Of)

#Basic Principles

• What They Do: Punnett squares are a tool to predict the probability of offspring genotypes and phenotypes based on the parents' genotypes. They are used for traits with simple inheritance patterns (dominant/recessive).

• How They Work:

  • Set up the square with one parent's alleles on top and the other parent's alleles on the side.
  • Fill in the boxes to show all possible combinations of alleles.
  • Calculate the probability of each genotype and phenotype.

  

  Image courtesy of WikiMedia Commons. Punnett squares help visualize the probability of different genotypes and phenotypes in offspring.

#Inheritance and Natural Selection

• Passing on Genes: The ability of parents to pass on their genes is the basis of natural selection. Individuals with advantageous traits are more likely to survive and reproduce, passing those traits to their offspring.

#Chromosomes: The Packaging of DNA

#Organization

• Why Chromosomes? DNA is coiled into chromosomes for easier distribution during cell division. It also helps us understand inheritance patterns.

• Genetic Disorders: Genetic disorders can arise from mutated alleles or nondisjunction (failure of chromosomes to separate properly during meiosis).

#Final Exam Focus

#High-Priority Topics

• Meiosis: Understand the steps of meiosis and how it leads to genetic variation.
• Punnett Squares: Be able to set up and interpret Punnett squares for monohybrid and dihybrid crosses.
• Sources of Variation: Know the mechanisms that generate genetic diversity (independent assortment, random fertilization, crossing over).
• Relationship between genotype and phenotype: Understand how genotype determines phenotype and how that is linked to natural selection.

#Common Question Types

• MCQs: Expect questions on the processes of meiosis and how they generate variation, Punnett square problems, and the relationship between genotype and phenotype.
• FRQs: Be prepared to explain how genetic variation arises, analyze inheritance patterns, and connect these concepts to natural selection and evolution.

#Last-Minute Tips

#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 sexually reproducing organisms? (A) Mitosis (B) Binary fission (C) Meiosis (D) DNA replication

Free Response Question

Describe the processes that contribute to genetic variation in sexually reproducing organisms. Explain how this variation is essential for the process of natural selection.

Scoring Guidelines

• Meiosis (2 points)
  • 1 point for describing how crossing over in prophase I increases genetic variation.
  • 1 point for describing how independent assortment of chromosomes in metaphase I increases genetic variation.
• Random Fertilization (1 point)
  • 1 point for explaining how random fertilization of egg and sperm increases genetic variation.
• Natural Selection (2 points)
  • 1 point for explaining that genetic variation provides the raw material for natural selection.
  • 1 point for explaining how natural selection acts on phenotypes, leading to differential survival and reproduction.

Good luck! You're going to do great! 👍