Genetics

Gregor Johann Mendel, an Austrian monk, is recognized as the Father of Genetics for his groundbreaking work on inheritance. In 1856, he published his findings on the principles of inheritance, which are now known as Mendel's laws. Although his work was initially overlooked, it was rediscovered by three biologists in 1900.

Mendel's experiments led him to discover that individual traits retain their physical identity during hybrid formation when inherited as discrete factors. These factors, which determine specific traits, are now known as genes, the basic unit of heredity.

Mendel chose Pisum sativum, commonly known as garden pea, for his experiments because of its various advantages, such as its distinct characteristics and ability to self-fertilize. He used this plant to study the inheritance of traits, which led to his discovery of the basic principles of genetics.

The incorrect statement about Pisum sativum is that it has a long life cycle. In reality, peas have a relatively short life cycle and are easy to cultivate. Additionally, they undergo self-fertilization, have bisexual flowers, and exhibit well-defined, discrete characteristics that made them an ideal species for genetics research.

Alleles are alternate forms of genes that occupy the same position on homologous chromosomes and are responsible for determining specific traits in an organism. They can be dominant or recessive and can result in different phenotypic expressions of a particular gene.

Reverse genetics is a type of genetic analysis where the genotype of an organism is inferred based on the phenotype it exhibits. In contrast, forward genetics is the process of identifying the genotype of an organism based on its observable traits or phenotype.

Mendel proposed three laws of inheritance, namely, the law of dominance, the law of segregation of gametes, and the law of independent assortment. The law of heterozygous is not one of Mendel's laws of inheritance.

The law of segregation is also known as the law of purity of gametes, as gametes always remain pure by separating the genes or factors at the time of gamete formation.

A dihybrid cross is the cross that involves the analysis of two independent traits. This law shows that during gametogenesis, the assortment of one pair of genes is independent of the other pair.

The semidominant allele produces its biochemical products in lesser quantity in comparison to a dominant allele. Thus the heterozygote is of intermediate intensity. For example, the cross of a red and a white flower gives a pink flower.

Gene interaction refers to the situation where the expression of one gene is affected by the presence of one or more other genes. Mendel observed that traits are inherited independently, but when traits are controlled by multiple genes, their inheritance follows the principle of gene interaction.

Complementary gene interaction is a type of gene interaction where two genes work together to produce a trait. In this interaction, one gene controls the production of an enzyme that is necessary for the expression of the trait, while the other gene controls the production of a substrate that the enzyme acts on. The 9:7 ratio shows that 9 offspring have both dominant genes, while 7 have either one dominant or both recessive.

Codominance is a type of inheritance where both alleles in a heterozygous individual are expressed equally. Unlike Mendelian inheritance, neither allele is dominant or recessive, and both traits are expressed in the offspring.

When two true breeding varieties of white flowered plants are crossed, the resulting progeny may not have white flowers. In some cases, the resulting flowers may be a different color, indicating that there is a complementary gene interaction between the alleles controlling flower color. This means that both alleles contribute to the production of a pigment required for the final color of the flower.

Epistasis is a type of gene interaction that involves the suppression of the effect of one gene by another non-allelic gene. It can result in the masking or modification of the expression of the gene. This type of interaction involves two pairs of alleles, and it can suppress both dominant or recessive alleles.

Epistasis is a type of gene interaction that involves the suppression of one gene's effect by another non-allelic gene. It can be of different types based on the ability of an allele in masking and modifying gene effects. The types of epistasis include dominant, recessive, complementary, and supplementary.

Masking gene interaction, also known as dominant epistasis, occurs when the dominant allele of one gene can mask the effect of either allele of the second gene. This type of interaction can be observed in the ratio of 12:3:1, which shows that dominant allele of one gene masks the effect of recessive alleles of the second gene.

Pleiotropy is the term used to describe the condition where either a single gene has multiple functions in the body or two genes have the same expression of a single character. This means that two different genes can have the same effect on a single trait.

Pseudoalleles are two types of alleles that have similar functions but different structures. These genes are located in close proximity, and their similarity in function can lead to confusion in genetic analysis.

Phenocopy is a type of phenotypic variation where a single trait of an organism is changed due to environmental effects. This effect is not hereditary and can be reversed when the environmental conditions are changed.

Linkage refers to the tendency of two or more genes to stay together during inheritance. Linkage can occur in two forms: cis and trans. In cis linkage, the two linked genes are present on the same chromosome and in trans linkage, the two linked genes are present on different chromosomes. Linkage is an important concept in genetics and helps in understanding the inheritance patterns of genes.

The linkage group refers to the group of genes that are physically linked together. The number of linkage groups represents the haploid number of chromosomes in a species. The linkage groups can be correlated as the number of homologous pairs. Therefore, option D, which states that linkage groups are not correlated with each other, is false.

Linkage maps are constructed by using recombination frequencies between genes. Recombination is the process by which two homologous chromosomes exchange genetic material during meiosis. The frequency of recombination between two genes is proportional to the distance between them on the chromosome. Therefore, linkage maps can be constructed by measuring the recombination frequencies between genes.

Linkage maps are constructed by using recombination frequencies between genes, which is determined by the test cross. The distance is measured in centi-morgan (cM), which represents the unit of the map. A centi-morgan is defined as the distance between two genes that have a 1% recombination frequency.

Recombination frequency is the measure of genetic linkage and represents the likelihood of a crossover event between two genes during meiosis. The maximum limit of recombination frequency between two genes is 50%, which means that they are located far apart from each other on the chromosome.

Linkage is the tendency of two or more than two genes to stay together during inheritance. It can be broken by the process of homologous recombination, which occurs during crossing over in the pachytene stage of prophase I. This results in the exchange of genetic material between homologous chromosomes, leading to a new combination of alleles.

Linkage of genes on chromosomes can result from the failure of independent assortment during the alignment of chromosomes in metaphase one. The other three laws do not directly result in linkage.

T.H. Morgan first studied linkage in Drosophila melanogaster, where genes on a chromosome are linked, creating a systemic gene. Morgan created the first genetic map of Drosophila melanogaster.

Recombination frequency measures the genetic linkage between two genes. A recombination frequency higher than 50% indicates that the two genes are not linked. Since 70cM is greater than 50%, the genes are unlinked, and the recombination frequency is 50%.

Hot spots on DNA are sites that have a high probability of crossing over during meiosis. In contrast, cold spots have a low probability of crossing over.

Sex-linked characters are those whose genes are located on the sex chromosome. According to modern genetics, the x-chromosome linked character is called a sex-linked character, while y-linked characters are called male-limited characters. This means that the correct answer is D, the sex chromosome.

In the case of sex linkage, reciprocal crosses do not yield identical results. Instead, they show a criss-cross inheritance pattern. This means that the answer to this question is B, false.

In the case of sex linkage, reciprocal crosses do not yield identical results. Instead, they show a criss-cross inheritance pattern. This means that the answer to this question is B, false.

Color blindness is an X-linked recessive disorder. In humans, three proteins in the cones act as color sensors, and two of these color sensors are encoded by X-linked genes. This means that the correct answer to this question is A, color blindness.

Partial sex linkage refers to the genes present in the terminal regions (PAR) of the sex chromosome. While the X and Y chromosome pair during meiosis and pairing occurs in the terminal region, the inheritance pattern of the genes in the PAR region is not like that of sex-linked genes. Instead, it resembles that of autosomal genes. Therefore, the statement in option C is incorrect.

Lesch-Nyhan syndrome is an X-linked disorder that causes excessive production of uric acid, known as congenital hyperuricemia. This disorder is caused by a defect in the HGPRT (Hypoxanthine Guanine Phosphoribosyl Transferase) gene. Therefore, the correct answer to this question is B.

Hunter syndrome is an X-linked recessive disorder that causes various symptoms, including abnormal hairiness, mental retardation, and a long protruding tongue. However, muscular deterioration is not a characteristic of Hunter syndrome but is a symptom of another disorder called Duncan muscular dystrophy. Therefore, the answer to this question is A.

Sex-limited traits are those which occur only in one sex or the other. For example, milk production is limited to females while musculature is limited to males. However, baldness is a sex-influenced trait, which means that its expression depends on the sex of the individual and also on other factors such as hormones, genetics, and environmental factors. Baldness occurs more commonly in males than females, but it is not a sex-limited trait.

Huntington's disease is an autosomal dominant disorder that is caused by an abnormal expansion of CAG trinucleotide repeats in the huntingtin gene. The normal range of CAG repeats in this gene is 10 to 35, but in individuals with Huntington's disease, the number of CAG repeats is greater than 40, leading to the production of a toxic protein that damages nerve cells in the brain.

Pedigree analysis is the study of inheritance patterns for genetic traits in families over several generations. It involves constructing a diagram (pedigree) that shows the relationships among family members and the inheritance of the trait of interest. Pedigree analysis can be used to determine the mode of inheritance (autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive) and to predict the probability of an individual inheriting the trait.