Monohybridism is a concept in genetics that refers to the study of a single pair of genes in a cross between individuals. In this type of inheritance, only one pair of alleles is considered, which facilitates understanding the patterns of genetic inheritance.
In this article, we'll explore what monohybridism is and how it manifests in different organisms. We'll also present solved exercises to help you consolidate the content and apply the concepts discussed in practice. Through these examples, you'll better understand how genetic traits are transmitted from one generation to the next and how genes are distributed during reproduction.
Understand the concept of monohybridism through a practical example.
Monohybridism is an important concept in genetics that refers to the analysis of a single pair of genes in a cross between individuals. In this type of cross, we observe the segregation of only one genetic trait.
A practical example to understand monohybridism is the cross between pea plants that have round seeds (dominant, represented by L) and plants that have wrinkled seeds (recessive, represented by l). By crossing a heterozygous plant (Ll) with a homozygous recessive plant (ll), we can observe how the alleles segregate in the offspring.
In the aforementioned cross, the probability of obtaining offspring with round seeds (genotype LL or Ll) is 50%, while the probability of obtaining offspring with wrinkled seeds (genotype ll) is also 50%. This occurs due to the principle of allele segregation during gamete formation.
Therefore, monohybridism allows us to understand how a single pair of genes behaves in a cross and how the alleles are transmitted to the offspring, following the laws of genetics formulated by Mendel.
Understanding the concept of Monohybrid crossing and its importance in genetics.
Monohybridism is a fundamental concept in genetics that refers to the study of crosses between individuals that differ in only one pair of genes. In this type of cross, individuals are homozygous for one gene and heterozygous for another. This allows us to analyze the inheritance of a single trait in a given population.
Monohybrid crosses are important in genetics because they allow us to understand the segregation of alleles and the transmission of genes from one generation to the next. Through this type of cross, it is possible to analyze the relationship between genes and their phenotypic effects, contributing to the advancement of knowledge about heredity and genetic variation.
To illustrate monohybridity, we can consider a cross between pea plants that differ in seed color. Suppose a homozygous green-seeded plant (VV) is crossed with a homozygous yellow-seeded plant (vv). The result of this cross will be a heterozygous F1 generation (Vv), where all individuals will have green seeds due to the dominance of the V allele over the v allele.
To determine the genotypic and phenotypic proportion of the F2 generation of this cross, we can use the Punnett square. Considering that the F1 individuals are heterozygous (Vv), we will have the following genotypic distribution: 1/4 homozygous dominant genotype (VV), 1/2 heterozygous genotype (Vv), and 1/4 homozygous recessive genotype (vv). Regarding the phenotype, we will have the following distribution: 3/4 green seeds and 1/4 yellow seeds.
Thus, the study of monohybridism through monohybrid crosses is essential for understanding the inheritance of a single trait and analyzing the transmission of genes from one generation to the next. Through this type of cross, it is possible to investigate the relationship between genes and phenotypes, contributing to the advancement of genetics and biology as a whole.
F1 and F2 in genetics: understanding generations and the inheritance of genetic traits.
In the study of genetics, it is essential to understand the meaning of F1 and F2, which represent different generations in crossbreeding experiments. The acronym F1 refers to the first filial generation, resulting from the cross between two parental organisms. In turn, the acronym F2 refers to the second filial generation, obtained from the crossbreeding of individuals from the F1 generation.
When it comes to the inheritance of genetic traits, monohybridism is a key concept. It involves the transmission of a single pair of genes from one generation to the next. In this type of cross, the organisms involved differ in only one pair of alleles for a specific trait.
To better understand monohybridism, practical exercises can be performed. For example, by crossing pea plants that are heterozygous for seed color (Aa), it is possible to predict the genotypic and phenotypic ratio of the offspring in the F2 generation. According to Mendel's laws, 25% of the offspring are expected to be homozygous dominant (AA), 50% heterozygous (Aa), and 25% homozygous recessive (aa).
Monohybridism: Understand the inheritance of a single gene in human genetics.
O monohybridism is a fundamental concept in genetics that refers to the inheritance of a single gene in organisms. In this case, we're talking about the transmission of a single pair of alleles of a specific gene from one generation to the next.
When an organism is monohybrid, means that it has two different alleles for a particular gene. An allele is the specific form of a gene, responsible for determining a specific characteristic of the organism. For example, the gene responsible for eye color may have one allele for blue eyes and another for brown eyes.
In single-gene inheritance, genetics follows Mendel's laws, which describe the segregation and distribution of alleles during gamete formation. Gametes contain only one allele of each gene, which will combine with the allele of the other parent during fertilization.
To better understand monohybridism, we can perform practical exercises that involve analyzing genetic crosses. For example, we can calculate the probability of a descendant inheriting a given allele from its parents, taking into account the possibilities of genetic combinations.
In summary, the monohybridism is essential for understanding the transmission of hereditary traits in humans and other organisms. By studying the inheritance of a single gene, we can unravel the genetic patterns that govern biological diversity within our species.
Monohybridism: what it consists of and solved exercises
O monohybridism refers to the crossing of two individuals that differ in only one trait. Similarly, when crossing individuals of the same species and studying the inheritance of a single trait, we speak of monohybridism.
Monohybrid crosses seek to investigate the genetic basis of traits determined by a single gene. The inheritance patterns of this type of crosslinking were described by Gregor Mendel (1822–1884), an iconic figure in the field of biology and known as the father of genetics.
Based on his work with pea plants ( Pisum sativum ), Gregor Mendel enunciated his well-known laws. Mendel's first law explains monohybrid crosses.
What does it consist of?
As mentioned earlier, monohybrid crosses are explained in Mendel's first law, which is described below:
Mendel's first law
In sexual organisms, there are pairs of alleles, or pairs of homologous chromosomes, which separate during the formation of gametes. Each gamete receives only one member of this pair. This law is known as the "law of segregation."
In other words, meiosis ensures that each gamete contains strictly one pair of alleles (variants or different forms of a gene), and it is equally likely that a gamete will contain either form of the gene.
Mendel was able to enunciate this law by crossbreeding purebred pea plants. Mendel tracked the inheritance of several pairs of contrasting traits (purple flowers versus white flowers, green seeds versus yellow seeds, long stems versus short stems) over several generations.
In these crosses, Mendel counted the offspring of each generation, obtaining individual proportions. Mendel's work yielded robust results, as he worked with a significant number of individuals, approximately a few thousand.
For example, in monohybrid crosses of round smooth seeds with wrinkled seeds, Mendel obtained 5474 round smooth seeds and 1850 wrinkled seeds.
Similarly, yellow seeds crossed with green seeds produce a number of 6022 yellow seeds and 2001 green seeds, thus establishing a clear 3:1 pattern.
One of the most important conclusions of this experiment was to postulate the existence of discrete particles that are passed from parents to offspring. Today, these inheritance particles are called genes.
Punnett photo
This chart was first used by geneticist Reginald Punnett. It is a graphical representation of individuals' gametes and all possible genotypes that can result from a cross of interest. It is a simple and quick method for solving crosses.
Solved exercises
First exercise
In the fruit fly ( Drosophila melanogaster ), the gray body color is dominant (D) over the black body color (d). If a geneticist makes a cross between a homozygous dominant (DD) individual and a homozygous recessive (dd) individual, what will the first generation of individuals be like?
Answer
The homozygous dominant individual produces only D gametes, while the homozygous recessive individual also produces only one type of gamete, but in their case, they are d.
After fertilization, all zygotes formed will have the genotype Dd. As for the phenotype, all individuals will have a gray body, since D is the dominant gene and masks the presence of d in the zygote.
In conclusion, we have 100% of individuals in F 1 will be gray.
2nd exercise
What proportions result from crossing the first generation of flies from the first exercise?
Answer
How to deduce flies F 1 has the genotype Dd. All resulting individuals are heterozygous for this element.
Each individual can produce gametes D and d. In this case, the exercise can be solved using the Punnett square:
In the second generation of flies, the characteristics of the parents (black-bodied flies) that seemed to have been “lost” in the first generation reappear.
We obtained 25% of flies with the homozygous dominant genotype (DD), whose phenotype is a gray body; 50% of heterozygous individuals (Dd), in which the phenotype is also gray; and another 25% of homozygous recessive individuals (dd), with a black body.
If we want to see it in terms of proportions, the crossing of heterozygotes results in 3 gray individuals versus 1 black (3:1).
Third exercise
In a certain variety of tropical silver, it is possible to distinguish between spotted leaves and smooth leaves (without spots, monochromatic).
Suppose a botanist crosses these varieties. The plants resulting from the first cross were allowed to self-fertilize. The result of the second generation was 240 plants with mottled leaves and 80 plants with smooth leaves. What was the phenotype of the first generation?
Answer
The key to solving this exercise is to take the numbers and convert them to proportions, dividing the numbers as follows: 80/80 = 1 and 240/80 = 3.
With the 3:1 pattern evident, it is easy to conclude that the individuals that gave rise to the second generation were heterozygous and had phenotypically spotted leaves.
Fourth exercise
A group of biologists studies the fur color of rabbits of the species Oryctolagus cuniculus . Apparently, coat color is determined by a locus with two alleles, A and a. The A allele is dominant and the A is recessive.
What genotype will the individuals resulting from the crossing of a homozygous recessive individual (aa) and a heterozygous individual (Aa) have?
Answer
The methodology to follow to solve this problem is to implement the Punnett square. Homozygous recessive individuals produce only a gametes, while heterozygous individuals produce both A and a gametes. Graphically, it looks like this:
Therefore, we can conclude that 50% of individuals will be heterozygous (Aa) and the other 50% will be homozygous recessive (aa).
Exceptions to the first law
There are certain genetic systems in which heterozygous individuals do not produce equal proportions of two different alleles in their gametes, as predicted by the Mendelian proportions described above.
This phenomenon is known as segregation distortion (or meiotic impulse ). An example of this are selfish genes, which interfere with the function of other genes seeking to increase their frequency. Note that the selfish element can decrease the biological effectiveness of the individual carrying it.
In the heterozygote, the selfish element interacts with the normal element. The selfish variant can destroy the normal element or prevent it from functioning. One of the immediate consequences is the violation of Mendel's first law.
References
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- Elston, R. C., Olson, J. M., & Palmer, L. (2002). Biostatistical genetics and genetic epidemiology . John Wiley & Sons.
- Hedrick, P. (2005). Population genetics . Third edition Jones and Bartlett Publishers.
- Montenegro, R. (2001). Human Evolutionary Biology National University of Córdoba.
- Subirana, J.C. (1983). Genetics Didactics . Editions Universitat Barcelona.
- Thomas, A. (2015). Introducing Genetics. Second Edition Garland Science, Taylor & Francis Group.