1. Chromosomes represent the densely packed form of DNA, facilitated by histone proteins H1, H2A, H2B, H3, and H4, visible during metaphase in cell division. 2. Eukaryotic chromosomes have two arms, termed p-arm and q-arm, with a central constriction called the centromere where spindle fibers attach during cell division. 3. The centromere’s location categorizes chromosomes … Read more
Males, with a single X and a Y chromosome, cannot be carriers for X-linked recessive disorders, as they lack another X chromosome to mask the expression of such genes. In females, having two X chromosomes allows them to be carriers without displaying physical traits, as one X can compensate for the recessive gene on the … Read more
Parthenogenesis is a form of asexual reproduction where embryos develop from unfertilized female gametes. Examples include honey bees, Aphis, wasps, and ants. The haplo-diploid method of sex determination in honey bee are: In honeybees, sex determination operates through haplodiploidy. Three distinct types of individuals emerge:Diploid queens (2n = 32), fully functional females originating from fertilized … Read more
A cross between F1 offspring and its homozygous recessive parent is called a test cross. Significance of testcross 1. Genotype Identification: Test cross helps determine the genotype of a plant expressing dominant traits, revealing whether it is homozygous or heterozygous. 2. Understanding Genetic Composition: It is a valuable tool for discerning the genetic makeup of plants, … Read more
Referred to as Mendel’s Second Law by Correns, The Law of Independent Assortment states that alleles from two pairs of traits segregate independently during gamete or spore formation. Subsequently, they undergo random rearrangement during fertilization, giving rise to both parental and novel trait combinations. Two crucial events occurs The independent separation of alleles for two … Read more
A dihybrid cross occurs when two pairs of alleles are involved, resulting in a phenotypic ratio of 9:3:3:1 in the F2 generation, known as the dihybrid ratio. For example, When we mate a true-breeding pea plant with round and yellow seeds with another true-breeding pea plant having wrinkled and green seeds, the offspring in the … Read more
The Chromosomal Theory establishes chromosomes as carriers of genetic material and puts forth the following principles: Hereditary traits are transmitted through gametes, the reproductive cells formed by the parents (sperms and ova), acting as a link between parents and offspring. Chromosomes within the nucleus of gametes serve as the vehicles for transmitting all hereditary characteristics. … Read more
Let’s compare the characteristics of X-chromosome and Y-chromosome: X-chromosome: 1. It is a straight, rod-like chromosome longer than the Y chromosome and is metacentric. 2. It contains a significant amount of euchromatin and a smaller amount of heterochromatin. 3. With a large DNA content, it is genetically active, housing numerous genes. 4. The non-homologous region is … Read more
Phenylketonuria (PKU) is a genetic condition due to a shortage of the enzyme phenylalanine hydroxylase. This deficiency leads to an accumulation of phenylalanine in the body, disrupting protein balance. Phenylalanine is found in all proteins and certain artificial sweeteners. The enzyme shortage hampers the conversion of phenylalanine into tyrosine, crucial for neurotransmitter production. PKU arises … Read more
Linkage in genetics means genes on the same chromosome tend to be inherited together, affecting how traits are passed down. Humans have 23 pairs of chromosomes. Each chromosome forms a linkage group. Therefore, there are 23 linkage groups in human beings.