Principles of Inheritance and Variation Flashcards
Heredity or Inheritance
Transmission of traits from one generation to the other (Parents or Offspring)
Variation
Difference in the genetic makeup of two individuals or between two organisms in a population
Name Mendel’s laws
IN CORRECT ORDER
- Law of dominance
- Law of segregation
- Law of independent assortment
Law of dominance
Out of the pair of alleles that represent a trait, one is dominant and the other is recessive
Law of segregation
When a pair of alleles are brought together, they remain together without blending, but separate completely during gamete formation
Law of independent assortment
The law of independent assortment states that the alleles of different genes are inherited independently within the organisms that reproduce sexually.
Reasons for success if using Pisum sativum for Mendel’s experiments
- Easy to cultivate
- Short life cycle
- Bisexual flowes
- True-breeding/pure plants that can be easily obtained through self-pollination
Father of genetics
Gregor mendel
Back cross
Crossing of a hybrid with any one of the parent
Test cross
Crossing of a hybrid with a recessive parent
Incomplete dominance
When a dominant allele, or form of a gene, does not completely dominate the effects of a recessive allele, and the organism’s resulting physical appearance shows a blending of both alleles
E.g. Incomplete dominance is exhibited in Snapdragon (Antirrhium) flower colour
Mirabilis jalapa
Multiple allelism
Condition where three or more alles are present for a particular gene.
E.g. Human blood group is governed by 3 alleles
IA, IB, i
Co-dominance
A condition wherein both alleles are equally expressed
E.g. Co-dominance is exhibited in AB blood group of ABO human blood group system
Punnett square
Checkerboard representation of all the possible phenotype and genotype combinations that can be formed in the progeny of a particular generation
Pleiotropy
The ability of a gene to influence more than one trait is called pleiotropy
E.g. Phenylketonuria
Starch synthesis in pea seeds
Pleoitropy with reference to PKU
PKU- phenylketonuria
in gene that codes for phenylalanine hydroxylase
Mutations to the gene result in:
Hair loss, skin pigmentation, mental retardation
Pleiotropy with reference to starch synthesis in pea seeds
BB: round, large seeds with more starch
Bb: round seeds with intermediate size starch grain
bb: wrinkled, small seeds with less starch
Crossing over
Exchange of genetic material during sexual reproduction between 2 homologous chromosomes’ non-sister chromatids that results in recombinant chromosomes
Takes place in zygotene of prophase 1 of meiosis 1
Linkage
Tendency of two or more genes of the same chromosome to remain together during the process of inheritance
Further the placement of genes in a chromosome less the chances of linkage
Colour blindness
Sex linked inheritance
* X-linked inheritance means the gene causing the disorder is in the X-chromosome
* X (recessive) genes in females will be expressed ONLY
if there are two copies of the gene (one on each
chromosome).
* In males, only one copy of the gene is required for the
disorder to be expressed.
Haemophilia
- Sex linked inheritance
- Blood borne disease
- Recessive trait (X- linked)
- Lacks the clotting factor (VII or IX) proteins responsible for clotting of blood.
- Prolonged bleeding leading to even death.
- Inheritance is similar, to that of Colour-blindness.
PKU- hereditary disorder
- Autosomal-linked recessive disorder
- Phenylalanine—> Tyrosine (Phenylalanine hydroxylase - enzyme)
Sickle cell anaemia
Autosomal-linked recessive disorder
Mutation in the 6th position of the Beta-globin chain of the haemoglobin molecule
Glutamic acid (GAG) —> Valine (GUG)
Base substitution- point mutation
Thalassemia
Autosomal-linked recessive disorder
Inherited blood disorder which is caused due to less amount of haemoglobin protein in blood
