Answer to Question #181620 in Genetics for John

Question

a) Outline Mendel's first law.

b) Briefly explain the terms,

• monohybrid inheritance

• dominant and recessive

• genotype and phenotype

• homozygous and heterozygous

Use specific examples with genetic notation to illustrate your answer and show links between the terms

Answer 1

a) The law of uniformity of hybrids of the first generation (Mendel's first law) - when crossing two homozygous organisms belonging to different pure lines and differing from each other in one pair of alternative manifestations of the trait, the entire first generation of hybrids (F1) will be uniform and will carry the manifestation of the trait of one of parents 

b) Monohybris inheritance - is the crossing of forms that differ from each other in one pair of studied alternative traits, for which the alleles of one gene are responsible.

Dominance, or dominant, is a form of relationship between alleles of one gene, in which one of them (dominant) suppresses (masks) the manifestation of the other (recessive) and thus determines the manifestation of a trait in both dominant homozygotes and heterozygotes. 

A recessive trait is a trait that does not manifest itself in heterozygous individuals due to the suppression of the manifestation of a recessive allele. 

Genotype is a set of genes of a given organism. The genotype, in contrast to the concept of the gene pool, characterizes an individual, not a species. In a narrower sense, a genotype is understood as a combination of alleles of a gene or locus in a particular organism. 

Phenotype is a set of external and internal characteristics of an organism acquired as a result of ontogenesis (individual development). 

Homozygous is a diploid organism or cell that carries identical alleles of a gene in homologous chromosomes (AA or aa). 

Heterozygous are called diploid or polyploid nuclei, cells or multicellular organisms, copies of genes that are represented by different alleles in homologous chromosomes. When a given organism is said to be heterozygous (or heterozygous for gene X), it means that copies of genes (or a given gene) in each of the homologous chromosomes are slightly different from each other. 

The connection between all these terms can be found in all three of Mendel's laws.