genetics

INHERITANCE OF TRAITS

• A sexually produced diploid ($2n$) organism is a result of the union of a haploid egg cell ($n$) and a haploid sperm cell ($n$).

• In humans, the normal diploid number of chromosomes is 46, half or 23 chromosomes were inherited from the father through the sperm cell, whereas the other 23 chromosomes were contributed by the mother through the egg cell.

• These chromosomes carry all the characteristics that will define the appearance, behavior, and physiological processes of the resulting organism.

Science of Genetics

• studies how these characteristics are inherited.

• addresses how other differences or variations occur in offsprings as a result of environmental and other nongenetic factors.

Chromosome

• made up of DNA molecules coiled around histones.

• the sequence of DNA bases in a chromosome will determine the codes of proteins responsible for the observable characteristics of an individual.

Gene

describes the specific sequence of DNA containing the information codes for protein.

Genome

• he set of genes found in a cell responsible for the characteristics of an individual.

• in sexually reproducing organisms, the genome is composed of two sets of chromosomes, paternal and maternal sets.

• thus, in a diploid ($2n$) individual, every chromosome is in pair.

Homologous chromosomes

refer to a pair of paternal and maternal chromosomes that are of the same size, similar gene locations also called loci (singular: locus), common banding patterns, and the same centromere location.

Alleles

one of two or more alternative forms of gene.

GENOTYPE

The totality of the genetic makeup of an individual. The combination of alleles found in a homologous chromosome. Represented by symbols.

HOMOZYGOUS

When two similar alleles are present in a pair

HETEROZYGOUS

When two different alleles are paired

PHENOTYPE

Refers to the observable expression of particular genotype

DOMINANT ALLELE

The allele that is expressed in a heterozygous condition

RECESSIVE ALLELE

The allele that is NOT expressed in a heterozygous condition

GREGOR JOHANN MENDEL

• father of Genetics

• an Augustinian monk who discovered the basic principles of heredity through experiments in his garden. Mendel's observations became the foundation of modern genetics and the study of heredity, and he is widely considered a pioneer in the field of genetics.

MONOHYBRID CROSS

• a cross involving a single trait or one trait inheritance

Law of Segregation

• the separation of homologous chromosomes, including the alleles contained therein during gamete formation.

Unit factors in pairs

The genetic characters are controlled by unit factors that exist in pairs in individual organisms.

DIHYBRID CROSS

a cross involving two traits

The Law of Independent Assortment

During gamete formation, segregating pairs of unit factors are assorted independently of each other.

• "During gamete formation, the gene pair assorts independently"

• The inheritance of one trait is not affected by the inheritance of another trait.