NESA Biology Genetic Variation

Incorrect. The geep receives 27 chromosomes from the sheep and 30 from the goat, making its total chromosome count 57, not a haploid number of 29.

Incorrect. The total chromosome count is determined by adding the haploid numbers of the parents ($27 + 30 = 57$), not 52.

Incorrect. This is the sum of the parents' diploid numbers ($54 + 60 = 114$). Fertilization involves the fusion of haploid gametes, not diploid cells.

Codominance occurs when both alleles of a single gene are fully expressed in the heterozygote (e.g., AB blood type), resulting in discrete phenotypes rather than continuous variation.

Incomplete dominance describes a single-gene interaction where the heterozygote is intermediate between homozygotes, but it does not produce the broad continuous variation caused by multiple genes.

Multiple allele inheritance refers to the presence of more than two alleles for a single gene within a population (e.g., ABO blood groups), which typically results in distinct categories rather than continuous variation.

Homologous chromosomes already contain the same genes in the same locations. Crossing-over exchanges different versions of those genes, not the genes themselves.

Crossing-over occurs specifically between homologous pairs, not random autosomal chromosomes, and it involves the exchange of alleles rather than genes.

While crossing-over can occur on autosomal chromosomes, it specifically requires homologous chromosome pairs. Furthermore, crossing-over also occurs between homologous regions of sex chromosomes.

This is incorrect because both Alpha and Beta Thalassemia are inherited as autosomal recessive conditions, not autosomal dominant.

This is incorrect because while Alpha Thalassemia involves four genes (two loci on chromosome 16), Beta Thalassemia involves only two genes (one locus on chromosome 11).

This is incorrect. Heterozygotes for Beta Thalassemia (Beta Thalassemia Minor) are typically asymptomatic or experience only mild anemia, making it non-fatal.

Crosses 2 and 3 show that when red and purple plants are crossed, all offspring are purple. This indicates that purple is the dominant trait and red is recessive.

Red is a recessive trait, not dominant. Additionally, reciprocal crosses (Crosses 2 and 3) yield the same results, which indicates the trait is autosomal rather than sex-linked.

If the trait were sex-linked recessive, Cross 3 (purple male crossed with red female) would produce red male offspring. Since all offspring are purple, the trait must be autosomal.

Co-dominance would result in offspring expressing both parental phenotypes simultaneously (e.g., leaves with both purple and green patches), rather than just one uniform phenotype.

The question explicitly states that both traits are controlled by alleles at specific genes, meaning they are genetically determined, not environmentally determined.

The question specifies that each trait is controlled by alleles at a "single gene," whereas polygenic traits are controlled by the interaction of multiple genes.

Incorrect. Fertilisation involves the random fusion of two haploid gametes to form a diploid zygote, rather than the random assortment of chromosomes during cell division.

Incorrect. Meiosis II involves the separation of sister chromatids, not the random assortment of homologous chromosome pairs, which already took place during meiosis I.

Incorrect. Mitosis produces genetically identical daughter cells and does not involve the pairing or random assortment of homologous chromosomes.

Binary fission is a form of asexual reproduction primarily used by prokaryotes to produce genetically identical offspring, so random assortment does not occur.

Fertilisation is the fusion of gametes to form a zygote. While it randomly combines genetic material from two parents, the actual random assortment of chromosomes happens earlier during gamete formation.

Mitosis is a process of cell division that produces genetically identical daughter cells, meaning chromosomes do not randomly assort to create genetic variation.

A single male rabbit carrying the recessive allele (either $Ll$ or $ll$) is sufficient to produce a mixed litter of long and short-furred offspring when mated with a heterozygous female.

The male rabbit could have had long fur if he was heterozygous ($Ll$), as he would still be able to pass on the recessive allele needed for short-furred offspring.

The male rabbit could be either homozygous recessive ($ll$) or heterozygous ($Ll$); he just needs to carry at least one recessive allele to produce short-furred offspring.

Sex-linked inheritance refers to genes located on the sex chromosomes (X or Y) and affects inheritance patterns based on biological sex, rather than causing continuous phenotypic variation.

Multiple allele inheritance involves a single gene having more than two alleles in the population (like ABO blood types), which typically results in distinct, discontinuous categories.

Incomplete dominance occurs when the heterozygote phenotype is an intermediate blend of the homozygotes, but it generally produces discrete phenotypes rather than a continuous spectrum.

Incorrect. The value 0.25 represents the proportion of offspring that inherit two copies of the lethal yellow allele and die before birth, not the proportion of surviving yellow offspring.

Incorrect. The value 0.33 (or 1/3) is the expected proportion of surviving offspring that have non-yellow fur, rather than yellow fur.

Incorrect. A proportion of 0.50 would be expected from a cross between a heterozygous yellow individual and a homozygous non-yellow individual, not a cross between two heterozygotes.

If the condition were sex-linked dominant, females would be more likely to inherit the condition than males because they have two X chromosomes.

Autosomal dominant conditions affect males and females at equal rates, which contradicts the fact that this condition is more common in males.

Autosomal recessive conditions affect males and females at equal rates, which contradicts the fact that this condition is more common in males.

This describes pleiotropy, where one gene affects multiple traits, rather than the expression of two different alleles for a single trait.

While the environment can influence some phenotypes, the simultaneous expression of both parental colors is a direct result of genetic inheritance, not environmental factors.

If both alleles were recessive, they would not both be visibly expressed in the offspring. Instead, both alleles are being expressed equally.