Mutations that result in the addition or deletion of a single base pair of DNA that changes the reading frame for the translation process as a result of which there is complete loss of normal protein structure and function are called Frameshift mutations.

Carica papaya, 2n = 36 (Papaya) has 17 pairs of auto somes and one pair of sex chromosomes. Male papaya plants have XY and female plants have XX. Unlike human sex chromosomes, papaya sex chromosomes look like auto somes and it is evolved from autosome. The sex chromosomes are functionally distinct because the Y chromosome carries the. genes for male organ development and X bears the female organ developmental genes. In papaya sex determination is controlled by three alleles. They are m, M, and M₂ of a single gene.

Multiple alleles of a series always occupy the same locus in the homologous chromosome. Therefore, no crossing over occurs within the alleles of a series.
(i) Multiple alleles are always responsible for the same character.
(ii) The wild type alleles of a series exhibit dominant character whereas mutant type will influence dominance or an intermediate phenotypic effect.
(iii) Proterminal synapsis: Pairing starts from the telomeres
(iv) Random synapsis: Pairing may start from anywhere.

(I) It is used to determine gene order, identify the locus of a gene and calculate the distances between genes.
(II) They are useful in predicting results of dihybrid and trihybrid crosses.
(III) It allows the geneticists to understand the overall genetic complexity of particular organism.

A more efficient mapping technique is to construct based on the results of three-point test cross. It refers to analyzing the inheritance patterns of three alleles by test crossing a triple recessive heterozygote with a triple recessive homozygote. It enables to determine the distance between the three alleles and the order in which they are located on the chromosome. Double cross overs can be detected which will provide more accurate map distances.

1. Single cross over: Formation of single chiasma and involves only two chromatids out of four.
2. Double cross over: Formation of two chiasmata and involves two or three or all four strands.
3. Multiple cross over: Formation of more than two chiasmata and crossing over frequency is extremely low.

After tetrad formation, crossing over occurs in pachytene stage. The non-sister chromatids of homologous pair make a contact at one or more points. These points of contact between non-sister chromatids of homologous chromosomes are called Chiasmata (singular-Chiasma). At chiasma, cross-shaped or X-shaped structures are formed, where breaking and rejoining of two chromatids occur. This results in reciprocal exchange of equal and corresponding segments between them.

Pairing of homologous chromosomes during zygotene stage of prophase I of meiosis I is called synapsis. Synapsis of three types:
1. Procentric synapsis: Pairing starts from middle of the chromosome.
2. Proterminal synapsis: Pairing starts from the telomeres.
3. Random synapsis: Pairing may start from anywhere.

If two linked genes are sufficiently apart, the chances of their separation are possible. As a result, parental and non-parental combinations are observed. The linked genes exhibit some crossing over. This phenomenon is called incomplete linkage. This was observed in maize. It was reported by Hutchinson.

The two dominant alleles or recessive alleles occur in the same homologous chromosomes, tend to inherit together into same gamete are called coupling or cis configuration. If dominant or recessive alleles are present on two different, but homologous chromosomes they inherit apart into different gamete are called repulsion or trans configuration.

(i) Somatic cells of organisms are derived from the zygote by repeated cell division (mitosis). these consist of two identical sets of chromosomes. One set is received from female parent (maternal) and the other from male parent (paternal). These two chromosomes constitute the homologous pair.
(ii) Chromosomes retain their structural uniqueness and individuality throughout the life cycle of an organism.
(iii) Each chromosome carries specific determiners or Mendelian factors which are now termed as genes.
(iv) The behaviour of chromosomes during the gamete formation (meiosis) provides evidence to the fact that genes or factors are located on chromosomes.