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Heredity, Genetics and DNA
Are my favorite things
The science of biological
inheritance
Genetics
Genetics Vocabulary
• Genetics is the study of heredity, a study
of how certain characteristics are passed
on from parents to children.
• A monk, Gregor Mendel, discovered the
basic principles of heredity in the 19th
century.
A HISTORY OF GENETICS
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A segment of a chromosome
that produces a particular trait.
Gene
A pair of hereditary factors that
make up a gene (different forms
of a gene)
Alleles
A hereditary factor that “takes
over” the gene determining the
trait
Dominant Allele
A hereditary factor that is
hidden by a dominant allele
Recessive Allele
Two identical alleles for a
particular trait. TT
Homozygous
Two different alleles for a
particular trait. Tt
Heterozygous
The genetic makeup of an
organism due to the genes
present
Genotype
A particular physical
appearance produced by genes
Phenotype
Male and female sex cells
gametes
A fertilized seed
Zygote
Genes
• Each trait – an expressed characteristic is
produced by a pair of hereditary factors
collectively know as GENES. Within a
chromosome, there are many genes, each
of which controls the inheritance of a
particular trait.
• A GENE is a segment of a chromosome
that produces a particular trait. For
example, in pea plants, there’s a gene on
the chromosome that holds the code for
seed coat color.
Alleles
• A gene usually consists of a pair of
hereditary factors called alleles. Each
organism carries two alleles for a particular
trait, one from the mother and one from the
father. Another way to say this is that two
alleles make up a gene, which in turn
produces a particular trait.
Alleles
• Dominant and RECESSIVE ALLELES: an
allele can be DOMINANT or RECESSIVE.
• A Dominant allele – takes over. Written
with a CAPITOL letter. T
• A Recessive allele – hidden by the
dominant. Written with a LOWERCASE
letter. t
Phenotype and Genotype
• When discussing the physical appearance
of an organism we refer to its phenotype.
• When talking about the genetic makeup of
an organism we refer to its genotype. The
genotype tells us which alleles the
organism possesses.
HOMOZYGOUS and HETEROZYGOUS
• When an organism has two identical
alleles for a given trait, we say the
organism is HOMOZYGOUS. For instance
TT and tt would both represent the
genotypes of homozygous organisms, one
homozygous dominant, and one
homozygous recessive.
• If an organism has two different alleles for
a given trai, say Tt, that organism is
heterozygous.
PARENT and FILLIAL GENERATIONS
• The first generation is always called the
parent or P1 GENERATION.
• The offspring of the P1 generation are
called the first fillial or F1 generation.
• The offspring of the F1 generation are
called the F2 generation.
Mendel’s Law of Heredity
1. Law of Segregation – states that the
members of each pair of alleles separate
when gametes are formed. A gamete will
receive one allele or the other.
2. Law of Independent Assortment – states
that two or more pairs of alleles segregate
independently of one another during
gamete formation.
The display of all the
chromosomes in a cell’s
nucleus
Karyotype