Mendelian and Non-Mendelian Inheritance

Gene

a unit of heredity

Allele

a version of a gene

Homozygous

organism with 2 identical alleles for given gene

Heterozygous

organism with 2 different alleles for a given gene

Genotype

genetic makeup

Phenotype

physical appearance

Dominant allele

expressed in phenotype

Recessive allele

expressed in phenotype in homozygous state

Monohybrid Cross

cross between individuals that are heterozygous for one character

Dihybrid

a cross between individuals that are heterozygous for 2 characters, 4 possible phenotypes. 16 possible genotypes

Advantages of pea plants

• observable traits

• cheap

• easy to grow

• grew rapidly

• produced many offspring

• easy to artificially fertilize

Principle of Segregation

inherited forms of traits segregate into gametes

Principle of Dominance

some alleles forms dominant, the organism expressed that phenotype, even when recessive allele is present

Principle of independent assortment

in dihybrid crosses, alleles segregate independently of each other pair of alleles during gamete formation, creating new combinations of traits in offspring that did not exist in parents

Test cross

to identify whether an organism showing the dominant phenotype is homo or hetero

• cross with a recessive

Human traits rarely follow…

Mendelian inheritance patterns

What usually follows Mendelian inheritance patterns in humans

mainly genetic diseases

Non Mendelian Inheritance

1. Incomplete Dominance

2. Codominance

3. Overdominance

4. Pleiotropy

5. Polygenic Inheritance

6. Environmental Effects

Incomplete Dominance

phenotype is somewhere between

• red plus white is pink

Codominance

two dominant alleles affect the phenotype in separate ways

• blood types

Overdominance

heterozygotes exhibits more extreme phenotypes than either homozygous parents

• middle parents is the preferred

Pleiotropy

most genes have multiple phenotypic traits

• a single gene may influence 2 or more phenotypic traits

Polygenic Inheritance

single trait controlled by multiple genes (skin color, eye color, hair color, etc)

Environmental effects

phenotype is affected by environment

Linked Genes

located on the sex chromosome that tend to be inherited together

• example: sex linked genes

Causes of genetic disorders

• inheritance of gene mutations

• Aneuploidy

Aneuploidy

alterations in chromosomes (number or structure) defective meiosis

Methods to predict genetic disorders

• genetic tests

• family pedigrees

• karyotypes