Mendellian Genetics

Character

Character

distinct heritable features (such as flower color)

Trait

character variants (such as purple or white flowers)

True Breeding

plants that produce offspring of the same variety when they self-pollinate  

P generation

the true breeding parents

F1

the hybrid offspring of the P generation

F2 generation

produced when F1 individuals self-pollinate/cross pollinate with other F1 hybrids   

Law of Segregation

states that during gamete formation, each parent passes one of their two copies of a gene to their offspring at random  

• According to this law, only one of the two gene copies present in an organism is distributed to each gamete that it makes 

• The two alleles for a heritable character separate during gamete formation and end up in different gametes  

• Corresponds to the distribution of homologous chromosomes to different gametes in meiosis 

Allele

alternative versions of a gene  

• Two of these are inherited, one from each parent 

Dominant Allele

determines the organism’s appearance if two alleles at a locus differ 

Recessive Allele

has no noticeable effect on appearance  

Homozygous/ Homozygote

an organism with two identical alleles for a character is said to be ____ for the gene controlling that character 

Homozygous dominant

two copies of the dominant form of a gene (TT)  

Homozygous recessive

two copies of the recessive form of the gene (tt)  

Heterozygous/heterozygote

two different genes (Tt): an organism that has two different alleles for a gene is said to be _____ for the gene controlling that character  

• Aren't true breeding  

Phenotype

the physical appearance (tall or short)  

Genotype

the letters that represent genetic makeup (TT, Tt, tt)

Test Cross

breeding the individual with a recessive homozygote is called a ____ because it can reveal the genotype of that organism  

Monohybrid/monohybrid cross

the F1 offpspring produced in this cross were ____, individuals that are heterozygous for one character  

• A cross betwen such hetereozygotes is called a ____ 

Dihybrid/ dihybrid cross

produced by crossing two true breeding parents differing in two characters in the F1 generation, heterozygous for both characters 

• A cross between F1 ____, can determine whether two characters are transmitted to offspring as package or independently 

Law of independent assortment

states that each pair of alleles segretgates independently of any other pair during gamete formation  

• Only applies to genes on chromosomes that are not homologous, or those far apart on the same chromosome 

• Genes located near each other on the same chromosome tend to be  inherited together

Complete dominance.

one form is completely dominant or completely recessive (red OR white)  

• Occurs when phenotypes of the heterozygote and dominant homozygote are indsitinguishable  

Incomplete dominance

mix of two traits (red + white = maroon)  

• The phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varietes  

Codominance

both traits are dominant, meaning you can see them simaltaneously (commonly seen with coloration of animals and the ABO blood type system) 

• Two dominant alleles affect the phenotype in separate, distinhuisable ways  

epistasis

a gene at one locus alters the phenotypic expression of a gene at a second locus

Polygenetic inheritance

an additive effect of two or more genes on a single phenotype 

Pedigree

a family tree that conmtains a family’s history for a particular trait  

Carrier

heterzygous individuals who carry the recessive allele but are phenotypically normal 

Multifactorial disorder

characters influenced by genetic and environmental factors collectively