Understanding Inheritance

Main Idea: The interactions among alleles, genes, and the environment

determine an organism’s traits.

Modeling Inheritance

A Punnett square is a model used to predict possible genotypes and

phenotypes of offspring.

Bb BbBb Bb

b b

B

B

PedigreesA pedigree shows genetic traits that

were inherited by members of a family tree. A pedigree usually only

indicates the phenotype of individuals. The genotypes of the individuals may not be known but

can often be determined.

Pedigrees, continuedBesides tracking common inherited

traits, pedigrees are important tools to track complex patterns of inheritance

and genetic disorders in families. https://youtu.be/Wuk0W10EveU

Pedigree example

Squares represent males. Circles represent females. Connected line

means relationship. Colored means has the trait. Semi-colored means

person is a carrier of the trait. Blank does not have the trait.

Complex patterns of Inheritance

Not all allele pairs have a dominant-recessive interaction. Some have

incomplete dominance and codominance interactions.

Incomplete Dominance

Sometimes traits appear to be blends of alleles. Alleles show incomplete dominance when they produce a phenotype that is a blend of the parents phenotypes.

Codominance

The human blood type AB is an example of another type of

interaction between two alleles. When both alleles can be observed in a phenotype, this type of interaction

is called codominance. If an individual inherits the B allele from one parent and an A allele from the

other parent, he or she will have type AB blood.

Multiple AllelesThe human ABO blood type is an example of a trait that is determined by multiple alleles. Even though there are multiple alleles, a person can

only inherit two of these alleles – one from each parent.

https://youtu.be/9O5JQqlngFY

Sex-Linked Inheritance

Traits may be sex-specific. Color blindness is an example of a sex-

linked trait. This is due to the fact that the Y chromosome is shorter than the

X chromosome. Therefore each of those genes has only one allele (on

the X chromosome).https://youtu.be/h2xufrHWG3E

Polygenic InheritanceTraits may be influenced by more than one gene. Height, weight, and

skin color are traits that are polygenic.

Human Genetic Disorders

An inherited mutation can result in a genetic disorder, which can result in

health problems. Some genetic disorders include Huntington’s

disease, sickle-cell, hemophelia, and Down syndrome.

Genes and the Environment

Traits might be influenced by the environment. Many genes affect a person’s chances of having heart disease. However, poor diet and

exercise can influence whether heart disease will develop.

Genes and the environment

These hydrangea plants are genetically identical. The acidic

conditions of the soil in which they grow determines flower color – more

acidic produces blue flowers.