Principles of inheritance and variation Flashcards
Gene
it is the basic unit of inheritance. contains the information on a particular trait
allelles
allelles are genes with 2 contrasting characteristics
homozygous
both allelles are identical
heterozygous
both allelles are non identical
dominant allelle
it is the allelle that expresses itself in homozygous as well as heterozygous.
recessive allelle
The factor which fails to express itself in the presence of its contrasting allele. A recessive factor expresses itself only in homozygous condition
Hybrid:-
Monohybrid cross:-
Dihybrid cross:-
The offspring produced by a cross between two individuals differing in one or more characters. Eg. Tt
Cross between two parents differing in one pair of contrasting characters. Eg. Tall * Dwarf
Cross between two parents differing in two pairs of contrasting characters. Eg. Tall Red * Dwarf White
true breeding line
having undergone continuous self pollination
ii. shows stable trait inheritance and expression for several
generations
LAW OF DOMINANCE
Characters are controlled by discrete units called factors.
Factors occur in pairs.
In a dissimilar pair of factors,one member of the pair dominates (dominant) the other (recessive)
LAW OF SEGREGATION
Two alleles of a pair representing a character, will segregate or separate from each other during gamete formation , so that a gamete receives only one of the two factors (never both).
The paired condition is restored during gamete fusion.
Mendel’s Law of Independent Assortment
When two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent of other pair of characters”.
INCOMPLETE DOMINANCE
Type of inheritance in which one allele is not completely dominant over the other.
MULTIPLE ALLELISM
Presence of more than two alleles for a gene
PLEIOTROPY
Phenomenon in which single gene exhibits multiple phenotypic expression.
Such a gene is called a pleiotropic gene.
Morgan worked with the tiny fruit flies Drosophila melanogaster.
. They could be grown in simple synthetic medium in the lab.
2. They complete their life cycle in about two weeks.
3. Single mating produces large number of progeny flies.
4. There is clear differentiation between the sexes.
5. It has many types of hereditary variations that
can be seen with low power microscope.
linkage
recombination
physical association of two genes
generation of non parental gene recombination’s
genetic maps
alfred sturtevant
frequency of recombination between gene pairs on the same chromosome as a measure of distance between genes and mapped.
polygenic traits
example
some traits are controlled by three or more genes and are thus called polygenic traits
pleiotropy
example
it is when a single gene exhibits multiple phenotypic expression
mutation
point mutation
alteration of DNA and consequently results on changes in the genotype and phenotype of an organism
a change in a a single base pair of DNA
pedigree analysis
analysis of traits in several generations of a family
mendelian disorders
chromosomal disorders
alteration or mutation in a single gene
caused due to absence of excess or abnormal arrangement of one or more chromosomes
color blindness haemophilia sickle cell anaemia phenylketonuria thalassemia
defect in recognizing red-green. x linked
x linked. clotting of blood is affected
autosome related shape of rbc to sickle shape
autosomal. mental retardation loss of hair and skin pigmentation
autosome. hemoglobin production is affected
aneuploidy
polyploidy
failure of segregation of chromatids during cell division results in the gain or loss of chromosomes.
failure of cytokinesis after telophase stage of cell division resulting in gain of extra set of chromosomes
