Week 6 Flashcards
Blending Theory
Blending theory is a pre-Mendelian concept.
* According to this theory, there is a blending effect of
parent factors or values that gives rise to a new
organism. This phenomenon includes incomplete
dominance of inheritance pattern.
* It is also called a non-Mendelian inheritance pattern.
It confers the fact that the offspring will inherit the
characteristics average of the parents for these
particular characteristics.
* E.g., Crossing the red flowers with white flowers
within the same species can give pink-colored flowers
as the progeny.
Trait
A trait is a specific characteristic of an organism.
Traits can be determined by genes or the environment,
or more commonly by interactions between them. The
genetic contribution to a trait is called the genotype.
The outward expression of the genotype is called the
phenotype.
Gene
The basic physical and functional unit of
heredity. Genes are made up of DNA. Some genes act
as instructions to make molecules called proteins
Allele
The basic physical and functional unit of
heredity. Genes are made up of DNA. Some genes act
as instructions to make molecules called proteins
Homozygote
having two identical alleles at corresponding loci on homologous chromosomes.
An individual who is homozygous for a trait has inherited from each parent one allele for that
trait
Heterozygote
Having different alleles at a given locus on the pair of homologous
chromosomes.
Carrier
An individual having one normal allele and one mutated allele does not have the
disease. Carriers are associated with diseases inherited as recessive traits. In order to have the
disease, an individual must have inherited mutated alleles from both parents.
Dominant
Dominant alleles show their
effect even if the individual only has one
copy of the allele. When an allele is
dominant, it is expressed in the
phenotype on a recessive allele
Recessive
Recessive refers to a type of
allele which will not be manifested in an
individual unless both of the individual’s
copies of that gene have that particular
genotype
Monohybrid
A monohybrid cross is a breeding experiment between P generation
(parental generation) organisms that differ in a single given trait.
o The P generation organisms are homozygous for the given trait.
o However, each parent possesses different alleles for that particular trait.
Dihybrid
A dihybrid cross is a breeding experiment between P generation (parental
generation) organisms that differ in two traits.
Gregor Mendel
(1822-1884) was an Austrian monk who discovered the basic rules of
inheritance. From 1858 to 1866, he bred garden peas in his monastery garden and
analyzed the offspring of these matings.
* His work is known as Mendelism. He laid down a foundation of Genetics hence he is
called Father of genetics.
What did he use for his experiments and why?
He used the garden pea, Pisum sativum.
Why was the Pea Plant Chosen?
* The garden pea was good choice of experimental organism because:
o many varieties were available that bred true for clear-cut, qualitative traits like
o seed texture (round vs wrinkled)
o seed color (green vs yellow)
o flower color (white vs purple)
o tall vs dwarf growth habit
o and three others that also varied in a qualitative — rather than quantitative — way.
* Peas are normally self-pollinated because the stamens and carpels are enclosed
within the petals. By removing the stamens from unripe flowers, Mendel could brush
pollen from another variety on the carpels when they ripened.
* By experimenting with true-breeding pea plants, Mendel avoided the appearance of
unexpected traits in offspring that might occur if the plants were not true breeding.
* The garden pea grows to maturity within one season, meaning that several
generations could be evaluated over a relatively short time.
* Large quantities of garden peas could be cultivated simultaneously, allowing Mendel
to conclude that his results did not come about simply by chance.
