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Heredity
 The characteristics of an organism are a result of
inherited traits received from parent(s).
The individuals in every population vary
from one another in their traits.
 Feature: A structure, characteristic, or behavior of an
organism, such as eye color, fur pattern, or timing of
migration.
 Trait: The specific way a feature is expressed in an
individual organism.
Heredity is the passing of physical and
mental characteristics from one generation
to the next.
Chromosomes are structures that contain hereditary
information and transfer it to the next generation; they
occur in nearly identical pairs in the nucleus of every cell.
DNA: deoxyribonucleic acid, a selfreplicating material present in nearly all
living organisms as the main constituent of
chromosomes. It is the carrier of genetic
information.
Genes are the basic units of heredity
carried by chromosomes. Genes code for
features of organisms.
Alleles are variations of genes that
determine traits in organisms: the two
alleles on paired chromosomes constitute a
gene.
An allele is one variant of a gene. Many
genes have two, several, or many variants
of the same basic genetic information.
Alleles can be dominant or recessive.
Dominant alleles exhibit their effect if they
are present on one chromosome; recessive
alleles exhibit their effect only when they
are on both chromosomes.
An organism’s particular combination of
paired alleles is it’s genotype; the traits
produced by those alleles result in the
organism’s phenotype.
A gene composed of two identical alleles
(e.g. both dominant or both recessive) is
homozygous; a gene composed of two
different alleles (i.e. one dominant and one
recessive) is heterozygous.
Gregor Mendel
 Gregor Mendel, known as the "father of modern
genetics," was born in Austria in 1822. A monk, Mendel
discovered the basic principles of heredity through
experiments in his monastery's garden. His
experiments showed that the inheritance of certain
traits in pea plants follows particular patterns,
subsequently becoming the foundation of modern
genetics and leading to the study of heredity.
 Biography Video
Law of Segregation
 During the formation of gametes (eggs or sperm),
the two alleles responsible for a trait separate from
each other. Alleles for a trait are then
"recombined" at fertilization, producing the
genotype for the traits of the offspring.
Law of Independent
Assortment
 separate genes for separate traits are passed
independently of one another from parents to offspring.
Law of Independent
Assortment
 This diagram illustrates a
dihybrid cross using a
Punnett square. The traits
are short tail (S), long tail (s),
brown coat (B) and white
coat (b).
Codominance
 In codominance both alleles for a trait are dominant.
 In codominance a heterozygous individual expresses
both simultaneously without any blending.
The prefix "co-" means "together". Cooperate =
work together. Coexist = exist together.
Codominance
Codominance- Roan Cattle