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
After syngamy, the zygote becomes active and starts dividing. 1. Cleavage: Cleavage is the initial mitotic division of the zygote, forming a hollow multicellular blastula. Blastomeres, the cells produced, decrease in size with each cleavage due to the absence of a growth phase. As size reduces, metabolic rates increase, leading to faster successive cleavages. This demands … Read more
Fertilization is the amazing process of combining male and female gametes to form a diploid zygote, crucial for human reproduction. This complex event usually happens in the ampulla of the fallopian or uterine tube, paving the way for the embryo’s development in the protective environment of the uterus. Sperm Movement towards Egg: The journey commences … Read more
The zygote divides to form two- celled proembryo. The larger cell positioned closer to the micropyle is termed the basal or suspensor initial cell, while the smaller cell closer to the chalaza is referred to as the terminal or embryonal initial cell. The suspensor cell divides in a single plane, transversely, leading to the formation … Read more
Pollen grain marks the begining of male gametophyte. First Mitotic Division During the initial mitotic division, it generates a larger, naked vegetative cell and a smaller, thinly-walled generative cell. The vegetative cell is rich in food and having irregular shaped nucleus. The generative cell floats in the cytoplasm of vegetative cell. Second Mitotic Division In … Read more