12.2 Characteristics and Traits
3 min read•june 14, 2024
Genetics is all about how traits get passed down from parents to kids. It's like a blueprint for life, with as the building blocks. Understanding how genes work helps us predict what traits offspring might inherit.
Sometimes inheritance follows simple rules, but other times it's more complex. Factors like and genes, , and mutations can shake things up. This diversity in makes genetics fascinating to study.
Mendelian Inheritance
Genotypes to phenotypes relationship
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- genetic makeup of an organism consists of alternative forms of a gene
- observable physical or biochemical characteristics determined by expression of alleles
- Dominant alleles (uppercase letters like A) mask expression of recessive alleles only one dominant allele needed for trait expression
- Recessive alleles (lowercase letters like a) only expressed when no dominant allele present two recessive alleles needed for trait expression
- dominant (AA) and homozygous recessive (aa) genotypes result in corresponding dominant and recessive phenotypes
- genotype (Aa) results in dominant phenotype due to dominance of A allele over a allele
Punnett squares for genetic prediction
- mates individuals differing in one trait
- Create Punnett square by determining parent genotypes, drawing 2x2 grid, writing alleles of one parent across top and other parent along left side, and filling in possible offspring genotypes
- proportion of each genotype in offspring (1 AA : 2 Aa : 1 aa)
- proportion of each phenotype in offspring (3 dominant : 1 recessive)
- predict probability of offspring genotypes and phenotypes based on parent genotypes
Purpose of test crosses
- determines genotype of individual with dominant phenotype by crossing with homozygous recessive individual
- Heterozygous (Aa) individual produces 1:1 ratio of dominant to recessive phenotypes in offspring when test crossed
- Homozygous dominant (AA) individual produces all dominant phenotype offspring when test crossed
- Perform test cross by:
- Crossing unknown genotype individual with homozygous recessive individual
- Observing offspring phenotypes
- Determining genotype based on offspring phenotypes
Non-Mendelian Inheritance
Mendelian vs non-Mendelian inheritance
- follows principles of dominance, segregation, independent assortment
- deviates from these principles includes and sex-linked traits
- Incomplete dominance neither allele completely dominant heterozygous individuals have intermediate phenotype (red RR and white WW flowers produce pink RW flowers)
- Sex-linked traits genes located on sex (X and Y) males have one X and one Y, females have two X
- traits more common in males who only need one recessive allele to express trait (color blindness, hemophilia)
Genetic Material and Inheritance
Heredity and genes
- is the passing of traits from parents to offspring
- Genes are segments of DNA that code for specific traits
- Genes are located on chromosomes, which are structures in the cell nucleus
- Chromosomes contain the genetic material (DNA) that is inherited
Mutations and inheritance patterns
- Mutations are changes in the DNA sequence that can alter genes
- Mutations can lead to new alleles and affect inheritance patterns
- Different inheritance patterns include:
- Autosomal dominant
- Autosomal recessive
- dominant
- X-linked recessive
Key Terms to Review (33)
Alleles: Alleles are different versions of a gene that exist at a specific locus on a chromosome. They can determine distinct traits or characteristics in an organism, influencing everything from flower color to disease resistance. The interaction between alleles—such as dominant and recessive relationships—plays a crucial role in inheritance patterns and genetic diversity.
Autosomes: Autosomes are chromosomes that are not sex chromosomes. They are present in pairs in both males and females and carry the bulk of an individual's genetic information.
Back mutations: Back mutations are genetic changes that restore the original sequence and function of a gene that had previously undergone mutation. These can occur naturally or be induced in a laboratory setting.
Chromosomes: Chromosomes are thread-like structures made of DNA and proteins that carry genetic information essential for heredity and the functioning of living organisms. Each species has a specific number of chromosomes, which play a crucial role during cell division, the inheritance of traits, and the overall expression of characteristics in an organism.
Codominance: Codominance is a form of inheritance where both alleles in a gene pair are fully expressed in the heterozygous condition. This results in offspring with a phenotype that shows both traits simultaneously without blending.
Dominant: In genetics, the term dominant refers to an allele that expresses its trait even when paired with a recessive allele. This characteristic means that when an organism carries one dominant allele and one recessive allele for a specific gene, the dominant trait will be the one observed in the phenotype. Dominant alleles can mask the presence of recessive alleles, leading to variations in inherited traits and characteristics.
Dominant lethal: A dominant lethal allele is a genetic variant that causes the death of an organism when present in a single copy. Such lethality typically occurs early in development, preventing the individual from surviving to reproduce.
Genes: Genes are segments of DNA that serve as the basic units of heredity, determining the traits and characteristics of an organism. They encode the information necessary for producing proteins, which play critical roles in cellular functions and overall development. Each gene can influence multiple traits, and their interactions contribute to the genetic variation observed within populations.
Genotype: A genotype refers to the specific genetic makeup of an organism, represented by the alleles inherited from its parents. It determines various traits and characteristics that an organism may express, linking it to patterns of inheritance and genetic diversity within populations.
Genotypic ratio: The genotypic ratio is a mathematical expression that shows the relative frequencies of different genotypes in the offspring produced from a genetic cross. It helps in predicting the genetic makeup of the next generation based on the alleles contributed by the parent organisms. Understanding this ratio is essential for grasping how traits are inherited and expressed in living organisms.
Hemizygous: Hemizygous refers to having only one allele of a gene instead of the typical two. This is often seen in males for genes located on the X chromosome, as they have only one X and one Y chromosome.
Heredity: Heredity is the biological process through which genetic traits and characteristics are passed from parents to their offspring. This transfer of genetic information is crucial in determining the physical and behavioral traits of an organism, influencing everything from eye color to susceptibility to certain diseases. Understanding heredity allows us to explore how traits are inherited and how they may affect individuals across generations.
Heterozygous: Heterozygous refers to an organism that has two different alleles for a specific gene, one inherited from each parent. This genetic diversity can influence the expression of traits and plays a key role in inheritance patterns, as seen in the way traits are passed down through generations and how they can vary among offspring. Understanding heterozygosity is essential for grasping concepts such as dominant and recessive traits, as well as predicting the likelihood of certain traits appearing in future generations.
Homozygous: Homozygous refers to having two identical alleles for a specific gene, meaning that an organism carries two copies of the same variant. This concept is crucial for understanding how traits are inherited and expressed, particularly in relation to dominant and recessive alleles. The significance of being homozygous is that it influences the expression of certain characteristics and traits in offspring, which can be predicted using probability laws.
Incomplete dominance: Incomplete dominance is a genetic situation in which one allele does not completely dominate another allele, resulting in a phenotype that is a blending of both traits. This phenomenon showcases how characteristics are inherited, allowing for a range of expressions rather than just dominant or recessive traits. It highlights the complexity of inheritance patterns and shows that traits can exhibit intermediate forms in offspring.
Inheritance patterns: Inheritance patterns refer to the ways in which genetic traits are transmitted from parents to offspring through generations. These patterns help explain the variability in traits among individuals within a population, providing insights into how genes interact and are expressed. Understanding these patterns is crucial for predicting traits in offspring and studying genetic diseases.
Mendelian inheritance: Mendelian inheritance is the set of principles that describe how traits are passed from parents to offspring through genes, based on the experiments conducted by Gregor Mendel in the 19th century. It highlights key concepts like dominant and recessive alleles, segregation, and independent assortment, which provide a framework for understanding genetic variation in organisms.
Monohybrid: A monohybrid cross involves the mating of two individuals with different alleles at one genetic locus of interest. The resulting offspring are studied to understand the inheritance of a single trait.
Monohybrid cross: A monohybrid cross is a genetic cross between two individuals that are both heterozygous for one particular trait, focusing on a single characteristic. This method allows researchers to observe how traits are inherited from parents to offspring and is foundational in understanding inheritance patterns and probabilities, as demonstrated through Mendel’s experiments. By examining the outcomes of a monohybrid cross, one can determine the dominant and recessive traits that emerge in subsequent generations.
Mutation: A mutation is a change in the DNA sequence of an organism's genome, which can lead to alterations in traits or characteristics. Mutations can occur spontaneously or be induced by environmental factors, and they play a crucial role in genetic diversity and evolution. They can be beneficial, harmful, or neutral, impacting an organism's ability to survive and reproduce in its environment.
Non-Mendelian inheritance: Non-Mendelian inheritance refers to patterns of genetic inheritance that do not follow the classical Mendelian laws of inheritance established by Gregor Mendel. This includes various mechanisms such as incomplete dominance, codominance, multiple alleles, and polygenic inheritance, which contribute to the complexity of traits in organisms. Understanding non-Mendelian inheritance is crucial for grasping how traits can be expressed in diverse ways beyond simple dominant and recessive patterns.
Pedigree analysis: Pedigree analysis is a diagrammatic method used to study the inheritance patterns of traits across generations in a family. It helps in identifying whether a trait is dominant, recessive, autosomal, or sex-linked.
Phenotype: A phenotype is the observable physical or biochemical characteristics of an organism, determined by both genetic makeup and environmental influences. It encompasses traits such as appearance, behavior, and physiological properties, highlighting how genes interact with the environment to shape an organism's characteristics.
Phenotypic ratio: The phenotypic ratio refers to the relative frequency of different phenotypes that are expressed in the offspring from a genetic cross. It provides a way to understand how traits manifest in physical forms and helps predict the likelihood of inheriting specific characteristics based on parental genotypes.
Punnett squares: Punnett squares are a diagrammatic tool used in genetics to predict the possible genotypes and phenotypes of offspring resulting from a genetic cross. They help visualize how alleles from each parent combine, showing all potential combinations in a grid format. This method is essential for understanding inheritance patterns and calculating probabilities of traits being expressed in the next generation.
Recessive: Recessive refers to a type of allele that must be present in two copies in order for a trait to be expressed in an organism. In other words, a recessive trait will only show up if an individual has inherited the same recessive allele from both parents, while the presence of a dominant allele can mask its expression. This concept is essential for understanding inheritance patterns and how traits are passed down through generations.
Recessive lethal: A recessive lethal allele is a type of genetic mutation that results in the death of an organism when present in a homozygous recessive state. Heterozygous individuals carrying one copy of the lethal allele typically survive and can pass the allele to their offspring.
Sex-linked traits: Sex-linked traits are characteristics that are associated with genes located on the sex chromosomes, primarily the X chromosome. These traits often show different patterns of inheritance in males and females due to the differences in their sex chromosomes, influencing the expression of certain genetic conditions and characteristics.
Test cross: A test cross is a breeding experiment used to determine the genotype of an individual with a dominant phenotype by crossing it with a homozygous recessive individual. This method helps reveal whether the dominant individual is homozygous or heterozygous for a specific trait, thus providing insight into the inheritance patterns observed in offspring. The results can clarify the underlying genetic mechanisms involved in traits, as well as their expression in different generations.
Variants: Variants are different forms or versions of a gene that arise due to mutations. They can result in diverse physical traits and characteristics within a species.
Wild type: Wild type refers to the phenotype of the typical form of a species as it occurs in nature. It represents the standard or norm for that species' genetic makeup and characteristics.
X-linked: X-linked refers to genes located on the X chromosome. These genes can exhibit unique patterns of inheritance, particularly affecting males more frequently due to their single X chromosome.
X-linked recessive: X-linked recessive refers to a pattern of inheritance in which a gene responsible for a trait or disorder is located on the X chromosome and is expressed in a recessive manner. This means that females, who have two X chromosomes, must inherit two copies of the mutated gene to express the trait, while males, having only one X chromosome, will express the trait if they inherit just one copy of the mutated gene. This inheritance pattern significantly impacts the expression of certain traits and disorders, often resulting in a higher prevalence in males compared to females.