Chapter 7a: Mendelian Genetics

Genetics

branch of biology concerned with hereditary and variation of inherited characteristics

William Harvey

an organism is derived from substances in the egg-embryotic development

John Dalton

the atomic theory

Louis Pasteur

the germ cell theory

Carolus Linneaus

all species are independently created

Jean-Baptiste Lamarck

environmentally induced behavioral changes lead the way in species change

Charles Darwin

species arose by descent with modification from other ancestral species

"Blending" theory of inheritance

genetic material contributed by the male and female parents mix in forming offspring

Inheritance of acquired characteristics

it was believed that an organism acquires some traits during its life time and they are then passed on to the offspring

Gergor Hohann Mendel

Austrian Monk who bred pea plants. Began experiments that lead to the study of inheritance

Mendels experimental materials - why he choose pea plants

Dilopid with two sets of chromosomes, self pollinated, can be cross polinated

Phenotype

Physical appearance of an organism expressed traits of an individual

Genotype

genetic makeup refers to alleles or varients ie AA Aa aa

Relationship between phenotype and genotype

genotype determines phenotype

Monohybrid cross

A cross between individuals that involves one pair of contrasting traits, can be clearly distinguished, have true breeding lines (genetically pure)

Cross(hybridization)

the cross fertilization of two different varieties/species

Hybrid

the offspring parents (P generation) of two different species

F1 generation

the first generation resulting from a cross

F2 generation

the next generation of plants from self fertilization of the F1 offspring

Alleles

alternative forms of a gene, which govern the variation of the same character that occupy corresponding positions on homologous chromosomes

homozgous

a true breeding organism having two identical alleles for a given characteristic

Heterozygous

having two different alleles for a given characteristic

Hemizygous

a condition in which only one copy of a gene or DNA sequence is present in diploid cells

Dominant allele

an allele that is always expressed when it is present, regardless of whether it is homozygous or heterozygous

Recessive allele

an allele that is not expressed in the heterozygous state

Punnet square

a tool to predict the probability of possible genotypes of offspring

Testcross

a cross of an individual of unknown genotype for a particular characteristic with a homozygous recessive individual

The law of segregation

when any individual produces gametes, the alleles separate, so that each gamete receives only one member of the pair of alleles

Two trait crosses

a genetic cross in which the parents differ with respects to the alleles of two loci(genes) of interest (dihybrid cross)

The Law of Independent Assortment

alleles of two or more different genes get sorted into gametes independently of one another

Incomplete dominance

a type of inheritance in which one allele for a specific trait is not completely expressed over its paired allele. Resulting in a third phenotype where the physical trait is a combination. (White flower + Red flower = Pink flower)

Codominance

a cross between organisms with two different phenotypes produced offspring with a third phenotype in which both traits appear. (Brown cow +white cow = spotted cow) THINK: Codominance is like coparenting; both need to be individually present)

Multiple alleles

occurrence of a gene that exists as three or more alleles in a population (ie. Blood types)

Pleiotropy

the determination of more than one character by a single gene (ie. Sickle cell effects many things)

Epistasis

occurs when 2 or more different gene loci contribute to the same phenotype, but not additively. Often described when one gene masks or modifies the phenotype of the second gene

Polygenic inheritance

the additive effect of two or more gene loci on a single phenotype characteristic (ie. human skin colour)