Answer to Question #176551 in Genetics for John

Question

Outline Mendel's first law.

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

(A) Mendel’s 1st law - state

(b) Accurate definition of each term and link between them

(c) Illustration and explanation of test cross.

(d) Explanation of multiple alleles and table

Answer 1

Mendel's First Law states that for the pair of alleles an individual has of some gene (or at some genetic locus), one is a copy of a randomly chosen one in the father of the individual, and the other if a copy of a randomly chosen one in the mother, and that a randomly chosen one will be copied.

Monohybrid cross is a type of hybridization experiment which involves the study of the inheritance of one pair of contrasting character. The alleles of contrasting characters selected in the monohybrid cross will show exact Dominance and Recessive relationships.

Dominant refers to the relationship between two versions of a gene. Individuals receive two versions of each gene, known as alleles, from each parent. If the alleles of a gene are different, one allele will be expressed; it is the dominant gene. The effect of the other allele, called recessive, is masked. For example, having a straight hairline is recessive, while having a widow's peak (a V-shaped hairline near the forehead) is dominant. Cleft chin, dimples, and freckles are similar examples; individuals with recessive alleles for a cleft chin, dimples, or freckles do not have these traits.

A genotype refers to the genetic characteristics of an organism. A phenotype refers to the physical characteristics. For example, having blue eyes (an autosomal recessive trait) is a phenotype; lacking the gene for brown eyes is a genotype. Genotype and phenotype are two fundamental terms in the science of genetics. An organism's genotype is the set of genes in its DNA responsible for a particular trait. An organism's phenotype is the physical expression of those genes.

Homozygous and heterozygous are terms that are used to describe allele pairs. Individuals carrying two identical alleles (RR or rr) are known as homozygous. While individual organisms bearing different alleles (Rr) are known as heterozygous. Heterozygous means that an organism has two different alleles of a gene. For example, pea plants can have red flowers and either be homozygous dominant (red-red), or heterozygous (red-white). If they have white flowers, then they are homozygous recessive (white-white). Carriers are always heterozygous.