Principles of Inheritance and Variation - Vocabulary Flashcards

Vocabulary flashcards covering key terms from Principles of Inheritance and Variation (CBSE Class 12 Biology).

Gregor Mendel

Father of Genetics; conducted pea experiments and formulated the basic laws of inheritance.

Genetics

Science that studies heredity and variation.

Inheritance

Process by which characters are passed from parent to offspring; basis of heredity.

Variation

Differences among offspring; can be morphological, physiological, cytological, or behavioral.

Alleles

Alternative forms of a gene that occur in pairs and determine trait variants.

Gene

Unit of inheritance; a DNA sequence that codes for a trait.

Locus

Position of a gene on a chromosome.

True breeding

Lines that, when self-pollinated, produce offspring identical to the parent; homozygous.

Emasculation

Removal of anthers to prevent self-pollination in breeding experiments.

Pollination

Transfer of pollen to the stigma, enabling fertilization.

Monohybrid cross

Cross studying one character; F1 all show dominant trait; F2 shows 3:1 phenotypic ratio.

Dihybrid cross

Cross studying two traits; follows Law of Independent Assortment; 9:3:3:1 phenotypic ratio.

Punnett square

A grid used to predict offspring genotypes and phenotypes from a cross.

F1 generation

First filial generation; offspring of the parental (P) generation.

F2 generation

Second filial generation; offspring of F1 cross.

Genotype

Genetic constitution of an individual (e.g., TT, Tt, tt).

Phenotype

Observable appearance or trait (e.g., tall, dwarf).

Homozygous

Two identical alleles for a gene (TT or tt).

Heterozygous

Two different alleles for a gene (Tt).

Dominant allele

Allele that expresses itself in the heterozygous state; shown by the uppercase letter.

Recessive allele

Allele that expresses only in the homozygous recessive state; masked in presence of dominant.

Law of Dominance

Dominant allele masks the effect of the recessive in a heterozygote; discrete factors.

Law of Segregation

Alleles separate during gamete formation; offspring inherit one allele from each parent.

Test cross

Cross between an individual with an unknown genotype and a homozygous recessive individual to determine homozygosity/heterozygosity.

Incomplete dominance

Neither allele is fully dominant; heterozygote shows an intermediate phenotype (e.g., pink flowers).

Co-dominance

Both alleles are expressed fully; no blending (e.g., ABO blood groups).

Multiple alleles

More than two alternative forms of a gene exist in a population (e.g., IA, IB, i in ABO).

Chromosomal Theory of Inheritance

Genes reside on chromosomes; chromosomes segregate during meiosis, explaining Mendelian inheritance.

Linkage

Genes located on the same chromosome tend to be inherited together; reduced recombination.

Crossing over

Exchange of chromosome segments between homologous non-sister chromatids during meiosis; increases variation.

Recombination

Generation of new allele combinations not seen in the parental types.

Sex determination

System by which sex is determined; humans: XY (male) and XX (female); others have XO or ZW systems.

Mutation

Permanent change in DNA sequence that alters genotype and phenotype.

Point mutation

Single base pair change in DNA (e.g., GAG to GUG in beta-globin gene).

Pedigree analysis

Study of trait transmission across generations in a family tree.

Mendelian disorders

Single-gene disorders; may be recessive or dominant; follow Mendelian inheritance (e.g., colour blindness, sickle cell).

Chromosomal disorders

Disorders due to abnormal chromosome number or structure (e.g., Down syndrome, Turner's, Klinefelter's).

Haemophilia

Sex-linked recessive bleeding disorder; carriers can transmit to sons.

Sickle cell anemia

Autosomal recessive; mutation in beta-globin (Glu to Val); red blood cells sickle under low oxygen.

Phenylketonuria

Autosomal recessive; lack of phenylalanine hydroxylase; leads to mental retardation if untreated.

Down's syndrome

Trisomy 21; features include short stature, distinctive facial features, intellectual disability.

Klinefelter’s syndrome

XXY in males; features include reduced fertility and sometimes secondary female traits.

Turner’s syndrome

XO in individuals; females; sterile and underdeveloped secondary sexual characteristics.

Gametes

Haploid reproductive cells (sperm and egg) carrying one allele per gene.

Aneuploidy

Loss or gain of one or more chromosomes; often causes disorders like Down syndrome.