Principles of Inheritance and Variation

A comprehensive set of question and answer flashcards based on lecture notes covering the principles of inheritance, Mendelian laws, chromosomal theory, and genetic disorders.

What is the branch of biology that deals with inheritance and the variation of characters from parents to offspring?

Genetics

How does the transcript define 'Inheritance'?

The process by which characters are passed on from parent to progeny; it is the basis of heredity.

What is 'Variation'?

The degree by which progeny differ from their parents.

During which years did Gregor Mendel conduct hybridization experiments on garden peas?

1856-1863

What is a 'true-breeding line'?

A line that, having undergone continuous self-pollination, shows the stable trait inheritance and expression for several generations.

How many pairs of contrasting traits in pea plants did Mendel study?

7

What are the units of inheritance that contain information required to express a particular trait?

Genes (formerly called 'factors' by Mendel).

What is the term for genes which code for a pair of contrasting traits?

Alleles

What is the difference between a 'homozygous' and a 'heterozygous' allelic pair?

Homozygous refers to identical alleles (e.g., $TT$ or $tt$), while heterozygous refers to dissimilar alleles (e.g., $Tt$).

What is the typical phenotypic and genotypic ratio of a Mendelian monohybrid F2 generation?

Phenotypic ratio of $3:1$ and a genotypic ratio of $1:2:1$.

Who developed the Punnett Square, and what is its purpose?

Reginald C. Punnett; it is a graphical representation used to calculate the probability of all possible genotypes of offspring in a genetic cross.

What is a 'test cross'?

A cross where an organism showing a dominant phenotype is crossed with the recessive parent to determine its genotype.

What does the 'Law of Segregation' state?

During gamete formation, the factors or alleles of a pair segregate from each other such that a gamete receives only one of the two factors.

Identify the example used in the text to describe 'incomplete dominance'.

The inheritance of flower colour in the dog flower (snapdragon or $Antirrhinum$ sp.).

In a cross between red ($RR$) and white ($rr$) snapdragons, what is the phenotype of the $F_1$ progeny?

Pink ($Rr$)

How is 'co-dominance' illustrated by human ABO blood groups?

When alleles $I^A$ and $I^B$ are present together, they both express their own types of sugars on red blood cells.

How many genotypes and phenotypes are possible in the human ABO blood group system?

6 genotypes and 4 phenotypes.

What does the 'Law of Independent Assortment' state?

When two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair of characters.

Who proposed the 'Chromosomal Theory of Inheritance' in 1902?

Walter Sutton and Theodore Boveri.

What organism did Thomas Hunt Morgan use for his experimental verification of the chromosomal theory?

$Drosophila\,melanogaster$ (tiny fruit flies).

Define 'Linkage' and 'Recombination' as coined by Morgan.

Linkage refers to the physical association of genes on a chromosome, while recombination describes the generation of non-parental gene combinations.

What is a 'polygenic trait'?

A trait controlled by three or more genes where the phenotype reflects the additive contribution of each allele (e.g., human skin color).

What is 'pleiotropy'?

A phenomenon where a single gene can exhibit multiple phenotypic expressions, such as in the disease phenylketonuria.

Who discovered the 'X body' (X-chromosome) in insects in 1891?

Henking

Describe the sex determination system in birds.

Female heterogamety, where females have $ZW$ chromosomes and males have $ZZ$ chromosomes.

What is the 'haplodiploid' sex-determination system in honey bees?

Offspring from the union of sperm and egg are diploid females (32 chromosomes), while unfertilised eggs develop via parthenogenesis into haploid males (16 chromosomes).

What is a 'point mutation'?

A change in a single base pair of DNA, such as in sickle-cell anemia.

What is 'pedigree analysis'?

The analysis of inheritance of a particular trait represented in a family tree over several generations.

Describe the molecular defect in sickle-cell anemia.

The substitution of Glutamic acid ($Glu$) by Valine ($Val$) at the sixth position of the $\beta$-globin chain of the haemoglobin molecule, caused by a GAG to GUG codon change.

How does Thalassemia differ from sickle-cell anemia?

Thalassemia is a quantitative problem (synthesising too few globin molecules), while sickle-cell anemia is a qualitative problem (incorrectly functioning globin).

What is 'aneuploidy'?

The gain or loss of a chromosome(s) due to the failure of chromatids to segregate during cell division.

What is 'polyploidy'?

An increase in a whole set of chromosomes caused by the failure of cytokinesis after the telophase stage.

What causes Down's Syndrome?

The presence of an additional copy of chromosome number 21 (trisomy of 21).

What are the characteristics of Klinefelter's Syndrome?

An additional X-chromosome (karyotype $47, XXY$), resulting in overall masculine development with expressed feminine features (e.g., Gynaecomastia) and sterility.

What causes Turner's Syndrome?

The absence of one of the X chromosomes, leading to a karyotype of $45$ with $X0$, resulting in sterile females with rudimentary ovaries.