Unit 5 Summary: Heredity

Overview

• Unit 5 topics cover 8-11% of the AP exam.
• Living things are classified into three domains: Archaea, Bacteria, and Eukarya.
• Heredity is the process of passing genetic information through DNA and RNA from one generation to the next.
• Evidence for common ancestry includes ribosomes, genetic code, and metabolic pathways.

Human Chromosomes

• Human karyotype: 23 pairs of homologous chromosomes.
• Chromosomes are inherited from parents' gametes, contributing to genetic variation.

Meiosis Process

• Purpose: Separate homologous pairs into gametes.
• Occurs in sex organs: testes and ovaries.
• Stages: Prophase, Metaphase, Anaphase, Telophase (PMAT), occurs twice in meiosis.
• Prophase 1: DNA condenses, nuclear membrane disappears, crossing over occurs (recombination).
• Metaphase 1: Homologous chromosomes align randomly (independent assortment).
• Anaphase 1: Homologous pairs separate.
• Telophase 1 & Cytokinesis: Two haploid daughter cells form.
• Meiosis 2: Similar to mitosis, results in four unique haploid cells.

Differences between Mitosis and Meiosis

• Mitosis: Growth, repair, asexual reproduction; results in two identical diploid cells.
• Meiosis: Forms gametes for sexual reproduction; results in four unique haploid cells.

Gregor Mendel and Genetic Laws

• Considered the father of heredity.
• Law of Independent Assortment: Genes on different chromosomes sort independently.
• Law of Segregation: Two alleles for each gene separate during meiosis.

Solving Genetic Problems

• Use Punnett squares to determine genotype and phenotype ratios.
• Monohybrid Cross: 1:2:1 genotypic ratio, 3:1 phenotypic ratio.
• Dihybrid Cross: 9:3:3:1 phenotypic ratio.

Non-Mendelian Genetics

• Incomplete Dominance: Neither allele is fully dominant; results in an intermediate phenotype (e.g., Snapdragon flowers).
• Codominance: Both alleles are expressed (e.g., blood types).
• Sex-Linked Traits: Traits located on sex chromosomes, often recessive and more common in males.
• Linked Genes: Genes close together on the same chromosome are inherited together.

Polygenic Traits

• Traits influenced by multiple genes (e.g., skin pigmentation, eye color).

Non-Nuclear Inheritance

• Mitochondria and chloroplasts have their own DNA, maternally inherited.

Environmental Influence on Phenotype

• Phenotypic plasticity: Organism exhibits different phenotypes in varying environments.

Genetic Disorders

• Non-disjunction: Failure of chromosomes to separate, leading to disorders (e.g., Down syndrome).
• Pedigrees: Analyze patterns of inheritance, determine autosomal vs. sex-linked, dominant vs. recessive.

Conclusion

• Meiosis increases genetic variation through crossing over, independent assortment, and random fertilization.
• Mendelian and non-Mendelian inheritance patterns include environmental influences.
• Practice using study guides, worksheets, and additional resources for further understanding.