Most Important Inheritance MCQs with Answers | Biology MCQs

Gregor Mendel conducted pioneering experiments with pea plants that laid the groundwork for modern genetics, hence earning him the title 'Father of Genetics'.

Genetics is the branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.

A locus is the specific physical location or position of a gene on a chromosome.

Alleles are alternative forms of a gene that are found at the same place on a chromosome.

All offspring in the F1 generation will be heterozygous (Tt) because 'T' is dominant over 't'.

For a monohybrid cross with COMPLETE DOMINANCE, the F2 phenotypic ratio is typically 3 dominant : 1 recessive.

Homozygous refers to an individual having two identical alleles for a specific gene (e.g., TT or tt).

Phenotype refers to the observable characteristics of an organism, resulting from gene expression and environmental factors.

An individual with two different alleles (Aa) is described as heterozygous.

Mendel's Law of Segregation states that during gamete formation, the two alleles for a heritable trait separate so each gamete gets only one allele.

A recessive allele only shows its effect when an organism has two copies of that allele, i.e., is homozygous recessive.

The genotypic ratio is 1 homozygous dominant : 2 heterozygous : 1 homozygous recessive.

The offspring will have a 1:2:1 genotypic ratio, so 1 out of 4 (25%) will be short (tt).

A dihybrid cross produces four distinct phenotypic combinations in the F2 generation in the ratio 9:3:3:1.

The 9:3:3:1 phenotypic ratio is seen in the F2 generation of a dihybrid cross between two heterozygous individuals.

This law explains how genes located on different chromosomes are inherited independently of one another.

Genes that are located close together on the same chromosome (linked genes) do not assort independently.

Dihybrid crosses show that traits controlled by different genes on separate chromosomes assort independently.

Independent assortment contributes to genetic diversity by producing new combinations of alleles in offspring.

Each RrYy parent can produce 4 unique gametes: RY, Ry, rY, and ry due to independent assortment.

9 both dominant : 3 first dominant, second recessive : 3 first recessive, second dominant : 1 both recessive.

The parent can produce AB and Ab gametes since AA only contributes A, and Bb contributes either B or b.

Independent assortment increases genetic variation by mixing alleles of genes on different chromosomes.

The probability of heads in one toss is 1/2. For two tosses: 1/2 × 1/2 = 1/4.

From the Punnett square: AA, Aa, Aa, aa → 1 out of 4 chance for AA, which is 1/4.

Using the product rule: 1/2 × 1/2 = 1/4 chance of inheriting both A and B.

A pedigree is used to track the inheritance of traits across generations in a family.

Each child has a 1/2 chance of being a girl. For three girls: 1/2 × 1/2 × 1/2 = 1/8.

In incomplete dominance, neither allele is completely dominant over the other, leading to a heterozygous phenotype that is an intermediate blend.

Flower color in 4 O'clock plants (Mirabilis jalapa) shows incomplete dominance, producing pink flowers from red and white parents.

Crossing RR and WW in incomplete dominance results in all heterozygous RW offspring, which are pink.

RW x RW gives genotypes: 1 RR (red), 2 RW (pink), 1 WW (white) — a 1:2:1 ratio.

In incomplete dominance, phenotypes match genotypes in a 1:2:1 ratio.

RW x WW → 50% RW (pink), 50% WW (white). So, 50% white flowers.

RW shows an intermediate phenotype — pink — in incomplete dominance.

In co-dominance, both alleles are fully and distinctly expressed in the heterozygote.

Both MN and ABO (specifically A & B alleles) are co-dominant systems.

LMLN genotype expresses both M and N antigens due to co-dominance.

Incomplete dominance results in blended phenotype; co-dominance results in both traits showing distinctly.

LMLN × LMLN yields LMLM, LMLN, and LNLN — classic 1:2:1 ratio.

Co-dominance results in both traits being fully and distinctly expressed.

Multiple alleles means more than two allele options exist in the gene pool, though each individual inherits only two.

ABO blood grouping is a classic example of multiple alleles (I^A, I^B, i).

There are three common alleles — I^A, I^B, and i — for ABO blood group determination.

Blood type A can be either I^AI^A (homozygous) or I^Ai (heterozygous).

AB blood type results from co-dominant alleles I^A and I^B being present together.

To produce an 'ii' child, both parents must pass on an 'i'. So the father must carry at least one 'i'.

The 'i' allele is recessive and only expresses the O phenotype when paired as ii.

Individuals with blood type B have B antigens on the surface of their red blood cells.

AB individuals have both A and B antigens and therefore lack anti-A and anti-B antibodies to prevent agglutination.

People with O blood type lack A and B antigens and produce both anti-A and anti-B antibodies.

O-negative blood lacks A, B, and Rh antigens, minimizing the risk of agglutination in recipients.

AB-positive individuals can receive any ABO or Rh blood type as they do not have anti-A, anti-B, or anti-Rh antibodies.

Anti-B antibodies in the recipient will attack B antigens, causing agglutination and a transfusion reaction.

B blood type results from either I B I B (homozygous) or I B i (heterozygous) genotypes.

If both A and B parents carry the recessive 'i' allele, their child can inherit ii and be type O.

Type O blood lacks both A and B surface antigens.

The Rh system is based on the D antigen. Its presence makes blood Rh-positive.

Exposure to Rh-positive blood causes the Rh-negative person to produce anti-Rh antibodies.

If the mother was sensitized in a previous pregnancy, anti-Rh antibodies can attack the second Rh-positive fetus's RBCs.

This condition arises in Rh-negative mothers with Rh-positive fetuses after sensitization in a prior pregnancy.

RhoGAM prevents sensitization of the Rh-negative mother's immune system to Rh-positive fetal cells.

Increased RBC production is a compensatory response, not a symptom. The condition is marked by anemia and jaundice.

The Rh factor is located on red blood cells and plays a major role in blood compatibility.

All offspring will be heterozygous (Rr) and thus Rh-positive.

The MN blood group is a classic example of co-dominance where both M and N antigens are expressed.

Minor blood group systems exist but typically do not interfere with standard blood transfusions.

The existence of over 200 minor blood groups highlights genetic diversity in blood typing.

Polygenic inheritance refers to the inheritance of quantitative traits (e.g., height, skin color) controlled by two or more genes, each contributing additively.

Human skin color shows continuous variation, characteristic of polygenic inheritance where multiple genes contribute.

Polygenic traits often show continuous variation and are influenced by environmental factors besides genetic contribution.

Multiple genes contributing additively to a trait indicate polygenic inheritance.

Grain color in wheat shows continuous variation controlled by multiple genes, a hallmark of polygenic inheritance.

Epistasis is when one gene masks or modifies the expression of another gene at a different locus.

In Labradors, the E/e gene is epistatic to B/b; ee genotype masks the B/b effect, resulting in yellow coat.

The gene that masks/modifies another's expression in epistasis is the epistatic gene.

Recessive epistasis typically shows a 9:3:4 phenotypic ratio.

Homozygous recessive cc masks the effect of gene A/a, an example of recessive epistasis.

Crossing over during meiosis causes exchange of chromosome segments, increasing genetic variation.

Crossing over breaks linkage and creates new allele combinations, increasing genetic diversity.

Genes far apart have high recombination frequency and behave like independently assorting genes.

Drosophila melanogaster (Fruit fly) is a key genetic model for studying linkage and recombination.

The Y chromosome carries the SRY gene responsible for male development.

Males have one X chromosome and no second sex chromosome (XO).

Autosomes are chromosomes not involved in sex determination.

Sex-linked traits are genes located on sex chromosomes, often X-linked.

Males express X-linked recessive disorders because they have only one X chromosome.

Red-green color blindness is an X-linked recessive disorder.

Holandric genes are Y-linked genes passed only from father to son.

Sex-influenced traits are autosomal traits expressed differently based on sex hormones.

Sex-limited traits express in only one sex even if gene is present in both.

Haemophilia is an X-linked recessive disorder, mainly affecting males.

A carrier mother has 50% chance of passing the affected X to a son, who will express the disorder.

Daughters have 50% chance of inheriting the affected X and becoming carriers.

In ZZ-ZW system, females are heterogametic (ZW) while males are homogametic (ZZ).

Sex-linked traits often show different expression in males and females due to chromosomal differences.

Sex-limited traits are expressed only in one sex despite being autosomal.