CH 5 | PRINCIPLES OF INHERITANCE

Law of Segregation

alleles separate during gamete formation

Law of Independent Assortment

genes assort independently

Law of Dominance

dominant allele masks recessive

Punnett Square

a genetic tool that helps predict the

possible offspring genotypes and

phenotypes by showing how

parental alleles can combine

Punnett Square

shows how alleles (gene variants)

from each parent can combine

Punnett Square

visual probability chart for genetics

Reginald C. Punnett

Who invented Punnett Square

Genotype

The genetic makeup of an organism

Phenotype

The observable

physical or biochemical

characteristics of an organism,

such as tallness or shortness

Complete dominance

only one allele in genotype is seen in the phenotype.

Incomplete Dominance

heterozygote shows intermediate trait

Codominance

both alleles expressed equally; two versions (alleles) of the same gene are expressed separately to yield different traits in an individual.

Multiple Alleles

more than two alleles control a trait (e.g., ABO blood

groups)

Polygenic Inheritance

multiple genes affect one trait (e.g., height, skin

color)

Epistasis

one gene masks the expression of another

Incomplete Dominance

All alleles are dominant for the trait but different.

Incomplete Dominance

Offspring have an appearance somewhat in between the phenotypes of the two parents mixed or blended

Type A

has A antigen on RBCs.

Type B

has B antigen on RBCs

Type AB

has both A and B antigens (codominance)

Type O

has no A or B antigen (only base H antigen).

Rh (Rhesus) system

second most important blood group system after ABO in

humans.

D antigen

is the most significant antigen in this system

Rh (D) antigen

is a protein found on the surface of red blood cells

(RBCs).

Rh-positive (Rh⁺)

If your red blood cells carry the D antigen, you are classified as

Rh-negative (Rh⁻)

If your red blood cells lack the D antigen, you are

hemolytic disease of the fetus and newborn

(HDFN)

If an Rh⁻ mother carries an Rh⁺ fetus, her immune system may

produce anti-D antibodies against fetal RBCs.

This can lead to ___________ in later pregnancies

anti-D immunoglobulin

HDFN can be prevented by giving

Polygenic inheritance

Human height, weight, and skin color are examples

Polygenes

Refer to a group of multiple genes that contribute to the expression of a specific trait or characteristic. It works together to influence a traits variation and complexity.

Single genes

Have a clear cut influence

Polygenic inheritance

a type of inheritance where

two or more genes (often located on different

chromosomes) collectively influence a single trait.

Mendelian traits

(controlled by a single gene with

dominant/recessive alleles), polygenic traits show a

range of phenotypes because multiple genes

contribute small additive effects.