Transcript Genes & Chromosomes

Genes &
Chromosomes
Chromosome Theory of
Heredity
 The factors (genes) that affect the
expression of traits are found on
chromosomes.
 The chromosome theory of heredity
states: That genes are located on the
chromosome and each gene occupies a
specific place on that chromosome.
Each chromosome contains just one
allele for each of its genes.
Crossing-Over
 Crossing-Over: The exchange of a
section of DNA between chromosomes.
 Recombinants: Individual organism with
a new combination of genes due to
crossing-over.
Mutations
 Mutation: Change in genetic material.
 Chromosomal Mutation: Change in number
or structure of chromosomes.
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Nondisjunction: Failure of chromosomes to
separate.
Polypoidy: Extra set of chromosomes.
 Gene Mutation: Change in the nucleotides of
DNA.
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Point mutations: Single nucleotide.
Frameshift mutation: The addition or deletion of a
base, altering DNA from the point of mutation on.
Sex Linkage
 Discovered by Nettie Stevens.
 Sex Chromosome: Chromosome that is
different in males (XY) and females (XX),
determine the sex of an organism.
 Autosomes: Chromosomes that are the same
in males and females.
 Sex-Linked: Trait that is determined by a gene
located on a sex chromosome.
Regulation of Gene
Expression
 Incomplete Dominance: Inheritance in which
an active allele does not entirely compensate
for an inactive allele, results in a mixed
phenotype (blended trait).
 Ex. Red Flower + White Flower = Pink
Flower
 Co-dominance: Condition in which both alleles
of a gene are expressed.

Ex. A person with one blue eye and one green eye.
 Polygenic Inheritance: A trait that is controlled
by a multiple alleles of a genes (3 or more).