2.1 Principles of Genetic Inheritance
3 min read•august 7, 2024
Genetic inheritance is the foundation of human development. It's all about how traits are passed down from parents to children through DNA, genes, and chromosomes. Understanding these basics helps explain why we look and function the way we do.
Inheritance patterns like dominant and recessive traits determine which characteristics show up in offspring. Cell division processes like and are crucial for growth and reproduction, shaping how genetic information is passed on and mixed up between generations.
Genetic Basics
DNA, Genes, and Chromosomes
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- DNA (deoxyribonucleic acid) contains the genetic instructions for the development, functioning, growth and reproduction of all known organisms
- DNA is made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T)
- Genes are segments of DNA that code for specific proteins and determine an organism's traits (eye color, height)
- Genes are located on chromosomes, which are thread-like structures located inside the nucleus of cells
- Humans have 23 pairs of chromosomes, for a total of 46 chromosomes
Alleles and Mutations
- Alleles are different versions of a gene that can result in variations in the trait controlled by that gene (brown eyes vs. blue eyes)
- Each individual inherits two alleles for each gene, one from each parent
- When the two alleles are different, one allele is expressed over the other (dominant vs. recessive)
- Mutations are changes in the DNA sequence that can lead to changes in gene function
- Mutations can be caused by errors during DNA replication or by environmental factors (UV radiation, chemicals)
Inheritance Patterns
Dominant and Recessive Traits
- Dominant traits are expressed when an individual has at least one dominant allele (brown eyes)
- Recessive traits are expressed only when an individual has two recessive alleles (blue eyes)
- refers to the genetic makeup of an individual, or the specific alleles they possess for a given trait (BB, Bb, bb)
- refers to the physical expression of a trait, which is determined by the genotype (brown eyes, blue eyes)
Mendelian and Polygenic Inheritance
- refers to the inheritance patterns first described by
- Mendel's laws state that traits are inherited in a predictable manner, with each parent contributing one allele for each trait
- Punnett squares can be used to predict the probability of offspring inheriting certain traits based on the genotypes of the parents
- involves traits that are influenced by multiple genes (height, skin color)
- Polygenic traits often result in a continuous range of phenotypes rather than distinct categories
Cell Division
Mitosis and Meiosis
- Mitosis is the process by which a cell divides into two genetically identical daughter cells
- Mitosis is used for growth, repair, and asexual reproduction
- The stages of mitosis are: prophase, metaphase, anaphase, and telophase
- Meiosis is the process by which a cell divides into four genetically distinct daughter cells, each with half the number of chromosomes as the parent cell
- Meiosis is used for sexual reproduction and produces (sperm and egg cells)
- The stages of meiosis are: meiosis I (prophase I, metaphase I, anaphase I, telophase I) and meiosis II (prophase II, metaphase II, anaphase II, telophase II)
- During meiosis, occurs, resulting in offspring with a unique combination of traits from both parents
Key Terms to Review (12)
Dominant Trait: A dominant trait is a genetic characteristic that is expressed in an individual even when only one copy of the gene responsible for that trait is present. This means that if an individual inherits a dominant allele from at least one parent, the corresponding phenotype will manifest. Understanding dominant traits is essential for grasping how certain characteristics are passed from one generation to the next and how they can influence the overall genetic makeup of a population.
Gametes: Gametes are specialized reproductive cells that carry half the genetic information of an organism, specifically one set of chromosomes. They play a crucial role in sexual reproduction, as they combine during fertilization to form a zygote, which eventually develops into a new organism. Understanding gametes is essential for grasping the principles of genetic inheritance, as they are the vehicles through which genetic traits are passed from parents to offspring.
Genetic Recombination: Genetic recombination is the process by which genetic material is physically mixed during the formation of gametes, resulting in offspring with combinations of traits different from those of their parents. This process occurs mainly during meiosis, where segments of DNA are exchanged between homologous chromosomes, leading to genetic diversity within a population and playing a crucial role in the principles of genetic inheritance.
Genotype: Genotype refers to the genetic makeup of an individual, specifically the alleles inherited from their parents. It represents the information encoded in an individual's DNA that determines traits, but it doesn't always dictate how those traits are expressed due to environmental influences. Understanding genotype is crucial for exploring how genetic inheritance works and its role in the nature vs. nurture debate.
Gregor Mendel: Gregor Mendel was a 19th-century scientist and Augustinian monk known as the father of genetics for his pioneering work on the inheritance of traits in pea plants. His experiments established foundational principles of genetic inheritance, such as the concepts of dominant and recessive traits, which have been essential for understanding heredity and variation in living organisms.
Meiosis: Meiosis is a specialized type of cell division that reduces the chromosome number by half, creating four genetically diverse haploid cells from an original diploid cell. This process is essential for sexual reproduction, as it leads to the formation of gametes—sperm and eggs—ensuring genetic variation in offspring. The two rounds of division in meiosis introduce recombination and independent assortment, which are key mechanisms for increasing genetic diversity.
Mendelian Inheritance: Mendelian inheritance refers to the principles of genetic inheritance first established by Gregor Mendel through his experiments with pea plants. It outlines how traits are passed from parents to offspring based on the segregation and independent assortment of alleles, forming the foundation for understanding genetics and heredity in all living organisms.
Mitosis: Mitosis is the process of cell division that results in two genetically identical daughter cells from a single parent cell. This process is crucial for growth, repair, and asexual reproduction in organisms, ensuring that each new cell maintains the same genetic material as the original. Mitosis is a vital part of the cell cycle, specifically occurring after DNA has been replicated during the synthesis phase, allowing for proper distribution of chromosomes to daughter cells.
Phenotype: Phenotype refers to the observable physical and behavioral traits of an organism, which result from the interaction of its genotype (genetic makeup) with the environment. This includes characteristics like height, eye color, and personality traits. Phenotypes can be influenced by various factors, leading to the understanding that both genetics and environmental conditions play significant roles in shaping who we are.
Polygenic Inheritance: Polygenic inheritance refers to the phenomenon where multiple genes contribute to the expression of a single trait, resulting in a continuous range of phenotypes rather than discrete categories. This concept is crucial for understanding complex traits, such as height, skin color, and intelligence, which are influenced by the additive effects of several genes and their interactions with environmental factors.
Punnett Square: A Punnett square is a grid-like tool used in genetics to predict the possible genotypes and phenotypes of offspring based on the genetic makeup of the parents. It visually represents the combination of alleles from each parent, helping to illustrate how traits are inherited according to Mendelian principles. By organizing the parental alleles in a systematic way, it provides insights into dominant and recessive traits and their probabilities in the next generation.
Recessive trait: A recessive trait is a characteristic that is expressed in an individual only when two copies of the corresponding gene are present, meaning both parents must pass on the recessive allele for the trait to be visible. This concept is fundamental in understanding genetic inheritance, as it illustrates how traits can skip generations and how certain traits can remain hidden in a population until conditions allow them to manifest.