12.3 Laws of Inheritance
4 min read•june 14, 2024
Mendelian genetics lays the foundation for understanding inheritance patterns. It explains how traits are passed down through generations, introducing key concepts like segregation and independent assortment. These principles help us predict offspring characteristics and understand genetic diversity.
Genetic interactions add complexity to inheritance patterns. , , and influence how traits are expressed and inherited. These phenomena explain deviations from expected Mendelian ratios and contribute to the vast diversity of life we observe.
Mendelian Genetics
Laws of segregation and assortment
Top images from around the web for Laws of segregation and assortment
Laws of Inheritance | Biology I View original
Is this image relevant?
28.6C: Mendel’s Law of Independent Assortment - Medicine LibreTexts View original
Is this image relevant?
The Process of Meiosis | OpenStax Biology 2e View original
Is this image relevant?
Laws of Inheritance | Biology I View original
Is this image relevant?
28.6C: Mendel’s Law of Independent Assortment - Medicine LibreTexts View original
Is this image relevant?
1 of 3
Top images from around the web for Laws of segregation and assortment
Laws of Inheritance | Biology I View original
Is this image relevant?
28.6C: Mendel’s Law of Independent Assortment - Medicine LibreTexts View original
Is this image relevant?
The Process of Meiosis | OpenStax Biology 2e View original
Is this image relevant?
Laws of Inheritance | Biology I View original
Is this image relevant?
28.6C: Mendel’s Law of Independent Assortment - Medicine LibreTexts View original
Is this image relevant?
1 of 3
- states that alleles for a gene segregate during gamete formation resulting in each gamete receiving only one for each gene
- Relates to the separation of homologous chromosomes during meiosis I ensuring that each gamete contains only one allele for each gene
- posits that alleles for different genes assort independently during gamete formation meaning the inheritance of one trait does not influence the inheritance of another trait
- Relates to the random alignment of homologous chromosome pairs during metaphase I of meiosis allowing for independent assortment of genes on different chromosomes
Probability in genetic crosses
- used to predict the probability of genotypes and phenotypes in a cross by creating a diagram with lines representing the possible gametes from each parent ()
- Lines are combined to determine the possible genotypes and phenotypes of the offspring providing a visual representation of the expected ratios
- Probability rules applied in genetic crosses to calculate the likelihood of specific genotypes or phenotypes
- used when calculating the probability of two or more independent events occurring together
- Example: probability of an offspring inheriting both a dominant allele from the mother and a recessive allele from the father
- used when calculating the probability of two or more mutually exclusive events occurring
- Example: probability of an offspring being either dominant or for a trait
- used when calculating the probability of two or more independent events occurring together
Genetic terminology and concepts
- Allele: Alternative forms of a gene that can occur at a specific locus
- : The genetic makeup of an organism, represented by the combination of alleles it possesses
- : The observable physical or biochemical characteristics of an organism, determined by its genotype and environmental factors
- Homozygous: Having identical alleles for a particular gene (e.g., AA or aa)
- Heterozygous: Having different alleles for a particular gene (e.g., Aa)
- : The relationship between alleles where one allele (dominant) masks the expression of another allele (recessive) in the heterozygous condition
Genetic Interactions
Gene linkage and recombination
- Gene occurs when genes are located close together on the same chromosome causing them to be inherited together and violating the
- Linked genes tend to be passed down as a unit from parent to offspring (red hair and freckles)
- Recombination is the exchange of genetic material between homologous chromosomes during meiosis specifically occurring during prophase I ()
- depends on the distance between genes on a chromosome with genes farther apart having a higher chance of recombination and genes closer together having a lower chance
- Impact on gamete formation
- Linked genes that do not undergo recombination will be inherited together in gametes maintaining their association in the offspring
- Recombination can lead to the formation of gametes with new combinations of alleles resulting in offspring with traits that differ from the parents (genetic diversity)
Epistasis in phenotypic expression
- is a form of gene interaction where one gene () influences the expression of another gene () with the phenotype being determined by the epistatic gene and masking the effects of the hypostatic gene
- Example: coat color in Labrador retrievers where the epistatic gene for the black/brown coat color masks the expression of the hypostatic gene for the yellow coat color
- Types of epistasis
- occurs when the presence of a dominant allele at one gene masks the expression of alleles at another gene (fruit color in summer squash)
- occurs when the presence of recessive alleles at one gene masks the expression of alleles at another gene (albinism in humans)
- Impact on phenotypic expression
- Expected phenotypic ratios in a cross may deviate from Mendelian ratios due to epistatic interactions leading to modified phenotypic ratios
- Presence of an epistatic gene can alter the phenotypic expression of the hypostatic gene resulting in unexpected phenotypes in the offspring ( in fruit color inheritance)
Key Terms to Review (29)
9:3:4 ratio: The 9:3:4 ratio is a specific phenotypic ratio that arises in the offspring of a dihybrid cross, specifically when examining traits governed by two genes that exhibit simple Mendelian inheritance patterns. This ratio indicates the proportion of different phenotypes among the offspring and typically reflects a situation where one gene is completely dominant over another, while the second gene can have multiple alleles or interactions. It highlights important genetic principles, including independent assortment and dominance relationships.
Addition rule: The addition rule is a principle used in genetics to determine the probability of obtaining any one of several possible outcomes. It is particularly important when dealing with inheritance patterns involving multiple traits or alleles. By applying this rule, one can calculate the likelihood of different genotypes or phenotypes occurring when different alleles are combined.
Allele: An allele is a variant form of a gene that can exist at a specific location on a chromosome. Alleles can be dominant or recessive, influencing the expression of traits in an organism. The combination of alleles inherited from parents determines an individual's genotype, which in turn affects their phenotype, or observable characteristics.
Crossing over: Crossing over is the process during meiosis where homologous chromosomes exchange segments of genetic material, leading to genetic variation in the resulting gametes. This genetic shuffling is crucial for sexual reproduction, enhancing diversity and influencing inheritance patterns, as it allows for new combinations of alleles to be passed on to offspring.
Dihybrid: A dihybrid is an organism that is heterozygous at two different genetic loci. It results from a cross between parents with different traits for both of these loci.
Dominance: Dominance is a genetic concept where one allele masks the expression of another allele for a given trait in a heterozygous individual. This masking effect means that the dominant allele's phenotype will be expressed, while the recessive allele's phenotype remains hidden. Understanding dominance is essential for predicting inheritance patterns and phenotypic ratios in offspring based on parental genotypes.
Dominant epistasis: Dominant epistasis is a genetic interaction where the presence of a dominant allele at one gene locus masks or suppresses the expression of alleles at a different locus. This phenomenon illustrates how certain genes can influence the phenotype by controlling other genes, highlighting the complexity of inheritance beyond simple Mendelian traits. Understanding dominant epistasis is crucial for grasping how traits are inherited and expressed in organisms, showcasing the interplay between different genetic factors.
Epistasis: Epistasis is a genetic interaction where one gene affects the expression of another gene. It can modify phenotypic ratios expected from Mendelian inheritance patterns.
Epistasis: Epistasis refers to a genetic phenomenon where the expression of one gene is affected by one or more other genes, leading to interactions that can mask or modify the phenotypic expression of traits. This concept is significant in understanding how genes can influence each other, affecting traits and inheritance patterns in an organism, which connects directly to the laws governing genetic inheritance.
Epistatic gene: An epistatic gene is a gene that can suppress or mask the expression of another gene at a different locus. This interaction is essential for understanding complex traits and inheritance patterns, as it highlights how multiple genes can influence a single phenotype. By affecting how traits are expressed, epistatic genes demonstrate the intricate relationships in genetic expression and variation.
Forked-line method: The forked-line method is a visual tool used in genetics to predict the possible genotypes and phenotypes of offspring based on parental traits. This method helps to simplify the process of determining genetic combinations by representing the different alleles in a branching format, making it easier to visualize inheritance patterns and ratios. It is particularly useful when dealing with multiple traits or genes in dihybrid and polygenic crosses.
Gene linkage: Gene linkage refers to the tendency of genes located close to each other on a chromosome to be inherited together during meiosis. This concept helps explain how certain traits are passed down together in offspring, illustrating the physical arrangement of genes within chromosomes and their impact on inheritance patterns.
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.
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.
Hypostatic gene: A hypostatic gene is a gene whose expression is masked or suppressed by the presence of an allelic variation at a different locus, known as an epistatic gene. This interaction can significantly influence the phenotype of an organism, demonstrating how multiple genes can contribute to observable traits. The concept of hypostatic genes is crucial in understanding inheritance patterns and gene interactions in organisms.
Law of dominance: The law of dominance states that in a heterozygote, one allele will mask the expression of another allele. This dominant allele will be expressed in the phenotype, while the recessive allele's effect is not observed.
Law of independent assortment: The law of independent assortment states that alleles for different genes segregate independently of one another during gamete formation. This principle applies to genes located on different chromosomes or far apart on the same chromosome.
Law of Independent Assortment: The Law of Independent Assortment states that the alleles for different traits segregate independently of one another during the formation of gametes. This principle, discovered by Gregor Mendel through his pea plant experiments, highlights how genes located on different chromosomes are inherited separately, which contributes to genetic variation in offspring.
Law of segregation: The law of segregation states that during the formation of gametes, the alleles for a trait separate so that offspring acquire one allele from each parent. This principle was first articulated by Gregor Mendel based on his work with pea plants.
Law of Segregation: The Law of Segregation is a fundamental principle of genetics stating that during the formation of gametes, the two alleles for a gene separate, so that each gamete carries only one allele for each gene. This process ensures that offspring inherit one allele from each parent, leading to the genetic diversity observed in traits. The law is a key concept stemming from Mendel’s experiments and it underpins the understanding of inheritance patterns.
Linkage: Linkage describes the tendency of genes located close to each other on the same chromosome to be inherited together during meiosis. It can affect the assortment of traits observed in offspring.
Multiplication rule: The multiplication rule is a fundamental principle in probability and genetics that states the probability of two independent events occurring together is the product of their individual probabilities. This concept is crucial in understanding how traits are inherited when dealing with multiple alleles, as it allows for the calculation of expected genetic outcomes in offspring based on parental genotypes.
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.
Punnett square: A Punnett square is a diagram used in genetics to predict the outcome of a particular genetic cross or breeding experiment. It allows for the visualization of the possible combinations of alleles from the parents, showing the likelihood of offspring inheriting specific traits based on Mendel’s principles of inheritance and the laws of probability.
Recessive epistasis: Recessive epistasis is a genetic interaction where one gene's recessive alleles mask or suppress the expression of another gene's alleles. This means that the phenotype associated with the dominant alleles of a second gene cannot be observed if the first gene carries two recessive alleles. Understanding this concept is crucial when studying inheritance patterns, as it illustrates how multiple genes can interact to influence traits in organisms.
Recombination: Recombination is the process by which genetic material is exchanged between homologous chromosomes during meiosis, resulting in new combinations of alleles. This process plays a vital role in increasing genetic diversity within populations, as it allows for the shuffling of genes, creating unique combinations that can be passed down to offspring and influencing traits across generations.
Recombination frequency: Recombination frequency is the proportion of recombinant offspring produced in a genetic cross. It measures the likelihood of crossing over between two genes during meiosis.
Recombination frequency: Recombination frequency is the measure of the likelihood that two alleles will be separated during meiosis due to the exchange of genetic material between homologous chromosomes. This concept is crucial in understanding genetic linkage, as it helps determine the distance between genes on a chromosome. A higher recombination frequency indicates that genes are farther apart, while a lower frequency suggests they are closer together.