Introduction to Inheritance

Inheritance

• The process by which characteristics of organisms are transmitted to their offspring.

• These characteristics are called genes.

• Genes are fragments of sequences of DNA.

• DNA contains genetic information and is organized in structures called chromosomes.

Chromosomes

• Are condensed DNA molecules

• It’s composed of 2 chromatids

• The center it’s called the centromere.

• Has a telomere that avoids each chromosome to stick with another.

• Chromosomes with the same arm length are called metacentric.

• Chromosomes with different arm lengths are called submetacentric.

• Chromosomes with short arm lengths are called acrocentric.

• Locus is the location of a specific gene in a chromosome.

• Alternative genes are called alleles.

• An organism with equal alleles for a pair of genes it’s called homozygous.

• An organism with different alleles for a pair of genes it’s called heterozygous.

• Homologous chromosomes: pair of chromosomes 1 maternal and 1 paternal with the same genes and different alleles.

Females’ chromosomes are XX and males are XY.

Mendel’s Laws of Inheritance

• Describe how genes are transmitted from one generation to another.

• Established by Gregorio Mendel aka the father of genetics.

• Genotype: a particular combination of alleles.

• Phenotype: traits such as blood type, enzymes, conduct, anything that can be observable and measurable.

• Punnet Squares: a method to predict genotype and phenotype of the offspring.

Law of Dominance

• 2 pure organisms with equal alleles cross.

• Pure organisms→AA, aa.

• 1st generation will have the same genotype and phenotype.

• Recessive alleles will mask.

Law of Segregation

• 2 organisms of 1st generation cross

• Recessive genes will express

• 3 dominants, 1 recessive

2 first laws were monohybrid crosses

Law of Independent Assortment

• Dihybrid cross.

• Traits can be gained independently.

• They can be inherited from mom, dad, grandpa, grandma, etc.

Transmission of other traits doesn’t affect.

Post-Mendelian Heredity

Exceptions to Mendel’s Laws

Incomplete Dominance:

• There is a third phenotype.

• Dominant gene doesn’t express completely.

• Both alleles manifest.

• For example a new color (let’s say there is no dominant gene).

Codominance:

• Both alleles express.

• Both genes are dominant.

• For example in dogs: white dogs, black dogs, black with white stains dogs, and white with black stains dogs can be born.