Genetics and Plant Breeding

Development of fruits happen by pollination but in some plants the embryo is aborted before developing into a seed. In parthenocarpy, seedlessness does not involve fertilization. Through stenospermocarpy, seedlessness can happen even after fertilization. Here, the embryo is aborted later after fruit formation by pollination. Examples of fruits with stenospermocarpy are Thompson and Flame seedless grapes.

Genetic recombination occurs during the pachytene stage of prophase I in meiosis, where crossing over takes place. This process is physically associated with the formation of chiasmata.

An allele is one of two or more forms of a gene. Sometimes, different alleles can result in different traits, such as colour. Other times, different alleles will have the same result in the expression of a gene.

Incomplete dominance is a type of inheritance in which one allele for a specific trait is not completely dominant over the other allele. This results in a combined phenotype (expressed physical trait). For example, if you cross pollinate red and white snapdragon plants, the dominant allele that produces the red color is not completely dominant over the recessive allele that produces the white color. The resulting offspring are pink.

Epistasis is an interaction between genotypes at two different gene loci, which sometimes resembles a dominance interaction at a single locus. Epistasis modifies the characteristic 9:3:3:1 ratio expected for two non-epistatic genes.

In case of autosomal dominant trait both the sexes are equally affected. Some autosomal dominant genes are preferentially expressed in one sex such as gout and pre-senile baldness affecting male.

This leads to variations in the population. Through the maternal gametes (ova) and paternal gametes (sperms), hereditary traits (characters) are passed on to child from parents. Genes are linearly arranged in chromosomes which are the carriers of hereditary traits. With the crossing over of two parental chromosome segments, a child inherits some of the traits from the mother and some from the father. This is why; two children from the same parents resemble each other in some characters and differ in others.

Heredity can be defined as the transmission of physical and mental characteristics from parents to offsprings. These characteristics can be called traits. These traits thus are transmitted from one generation to the next.

Linkage group is equal to haploid set of chromosome, but since in male there is Y chromosome, so total linkage group will be 23 + 1 = 24.

2n = 6x = 42 Therefore 42 / 6 = 7. Thus 7 linkage group.

The most prevalent type of consanguineous marriage, show that the excess risk for their offspring of having a significant birth defect ranges from 1.7-2.8%.

The Rh blood factor is a dominant trait. Therefore, both DD and Dd people have the Rh antigen on the surface of their red cells which makes them Rh positive.

A homozygous genotype refers to the inheritance of the same allele for a trait from both parents.

DNA sequence comparison is considered to be far more reliable than one of the other forms of evidence in predicting who could or could not be a parent of a particular child.

According to Mendel's law of independent assortment, this cross shows the progeny in the phenotypic ratio of 9 : 3 : 3 : 1. This is the law related to dihybrid cross.