Understanding Genetic Inheritance: IB Biology

Welcome to the fascinating world of genetic inheritance!Our journey begins with Gregor Mendel, an Austrian monk who revolutionized our understanding of inheritance through his experiments with pea plants.Mendel worked with pea plants, studying various traits including plant height. He observed that some traits were dominant over others.He discovered that genes come in different forms called alleles. Capital T represents the dominant tall allele, while lowercase t represents the recessive short allele.To understand how these alleles combine in offspring, we use a Punnett square. This tool helps us predict all possible combinations of alleles.The genotype, or genetic makeup, determines the phenotype, or physical appearance of the plant.Plants with at least one dominant T allele will be tall, while only plants with two recessive t alleles will be short.In incomplete dominance, neither allele is completely dominant. Let's look at snapdragons as an example.When a red snapdragon is crossed with a white snapdragon, the offspring are pink, showing a blend of the parental traits.Codominance is different - both alleles are expressed equally. Blood types are a perfect example.In type AB blood, both A and B antigens are fully expressed on the surface of red blood cells.Some traits are controlled by multiple alleles of the same gene. Rabbit coat color is a classic example.Sex-linked inheritance occurs when genes are located on sex chromosomes. Many traits are carried on the X chromosome.Female carriers have one normal and one affected X chromosome, while males have only one X chromosome, making them more susceptible to sex-linked disorders.Polygenic inheritance occurs when multiple genes influence a single trait, like human height.Each gene contributes a small effect to the overall trait, creating a bell-shaped distribution in the population.Environmental factors also play a crucial role in how genes are expressed.Modern genetic screening allows us to analyze DNA for potential genetic disorders.Genetic counselors help individuals and families understand their genetic risks and make informed decisions.In agriculture, understanding inheritance patterns helps develop improved crop varieties with better yields and disease resistance.