Sindh Mdcat Exclusive Course Biology Inheritance — Solved MCQs

Question 1

In the pedigree of a family shown above, brown eyes are indicated as white circles and blue eyes as dark circles. Javeria and Juhi are twins. From this chart, it can be determined that:

Accepted Answer

D. Juhi is homozygous for blue eyes — It is imperative for a recessive trait present in a homozygous state to show up in phenotype so answer D is correct.

Question 2

Which trait is not sex-linked recessive:

Accepted Answer

C. Hypophosphatemia — This is correct answer as hypophosphatemia is an sex-linked dominant disease not recessive.

Question 3

The gene which controls the ABO group has how many alleles in an individual?

Accepted Answer

B. 2 — ABO blood groups in humans are controlled by the gene I. It has three alleles: IA, IB, and i. Since, there are three different alleles, six different genotypes are possible. However, a single individual has two ABO blood type alleles, because we each inherit one blood type allele from our biological mother and one from our biological father. Hence, the correct answer is B.

Question 4

A pure breeding plant with the dominant phenotype of character P and the recessive phenotype of character Q was crossed with another pure breeding plant with the recessive phenotype of character P and the dominant phenotype of Q. The offspring of this cross were crossed with a double homozygous recessive for P and Q and the following results were obtained:22 were phenotypically dominant for P and recessive for Q5 were phenotypically dominant for both P and Q4 were phenotypically recessive for both P and Q24 were phenotypically recessive for P and dominant for QWhich one of the following types of Inheritance is illustrated by these results?

Accepted Answer

A. Gene linkage of P and Q — When a pure breeding phenotypic dominant character P and recessive character Q is crossed with pure breeding recessive character P and dominant character Q, the cross is below:- PPqq X ppQQ will give PpQq. Now when this PpQq is crossed with recessive for both:- PpQq X ppqq will give PpQq ; Ppqq ; ppqq ; ppQq The ratio when there is a dihybrid cross between heterozygous character and homozygous recessive character is 9:3:3:1. However, the above ratio is not consistent with what it should be. This happens when there is a gene linkage between two characters

Question 5

Flower color is controlled by a single pair of alleles. The allele for red flowers is dominant to the allele for white flowers. A plant homozygous for red flowers is crossed with a plant homozygous for white flowers. All the resulting plants have red flowers (F1 generation). When the F1 generation crosses with each other, 18 plants are obtained. 12 plants have red flowers and 6 have white flowers (F2 generation). What ratio is expected in the F2 generation and what ratio has been obtained?

Accepted Answer

A. 3:1 expected, 2:1 obtained — The correct answer is that the expected ratio in the F2 generation is 3:1, and the obtained ratio is 2:1. In a typical Mendelian monohybrid cross (Rr x Rr), the expected phenotypic ratio is 3:1, with three plants having the dominant phenotype (red flowers) for every one plant with the recessive phenotype (white flowers). The obtained ratio of 2:1 suggests a deviation from the expected, possibly due to a small sample size or experimental error. The other options incorrectly present the expected and obtained ratios.

Question 6

Consider the following statements about biological communities.I. Their members share a common gene poolII. The community remains stable even though some physical aspect of the environment may undergo a changeIII. It consists of all the populations living in a particular area.IV. A community interacts with a non-living environment and both function together to form an ecosystemWhich two of the above statements are true?

Accepted Answer

E. 3 and 4 — Different living and nonliving things in a single habitat form a single community. Since different species are present they have different characteristics so the gene pool is not the same. Change in the environment does cause a change in the balance of genes in the environment so the community does not remain stable.The last two statements iii and iv are right that as previously mentioned the community is all the population living in a particular area. Secondly, the community involves biotic(living) and abiotic(non-living) factors interacting with one another.

Question 7

In birds the male is the homogametic sex. A male bird showing the recessive trait was mated with a female showing the dominant trait of a characteristic governed by a pair of alleles which are sex-linked. What is the probability that the male offspring will show the dominant trait?

Accepted Answer

E. 1.00 — In this problem, we are dealing with a sex-linked trait where the male parent (XbY) carries the recessive allele (b), and the female parent (XBXB) has two dominant alleles (B). The key is to recognize that in birds, males are homogametic, meaning they have two identical sex chromosomes (XY), while females have two different sex chromosomes (XX).The cross between the male (XbY) and the female (XBXB) yields the following gametes:Xb from the male and XB from the female leads to XbXB (female with dominant trait)Xb from the male and XB from the female leads to XbXB (female with dominant trait)Y from the male and XB from the female leads to XBY (male with dominant trait)Y from the male and XB from the female leads to XBY (male with dominant trait)Thus, all male offspring (XBY) will inherit the dominant allele from the mother, resulting in a probability of 1.00 that they will express the dominant trait.The other options are incorrect because they misinterpret the inheritance pattern and the genotypes of the parents involved in the cross.

Question 8

“Law of independent assortment” states:

Accepted Answer

A. That each pair of alleles assort independently of other pairs of alleles during gamete formation — Mendel's law of independent assortment states that the alleles of two (or more) different genes get sorted into gametes independently of one another. In other words, the allele a gamete receives for one gene does not influence the allele received for another gene.

Question 9

In 'Complete Dominance':

Accepted Answer

B. One allele (R) is completely dominant over the other (r) — Complete dominance is a form of dominance in a heterozygous condition wherein the allele that is regarded as dominant completely masks the effect of the allele that is recessive. Option C refers to 'Incomplete Dominance' where a dominant allele, or form of a gene, does not completely mask the effects of a recessive allele, and the organism's resulting physical appearance shows a blending of both alleles.

Question 10

Which statement about dominant and recessive alleles is not correct?

Accepted Answer

D. The phenotype of a homozygote is always dominant. — Phenotype of a homozygote can be dominant or recessive both AA or aa. Hence statement D is incorrect and our answer.

Question 11

Pick the correct option for Drosophila.

Accepted Answer

D. Salivary gland cells have giant chromosomes in their nuclei — Polytene chromosomes form in the Drosophila giant salivary gland during development by multiple rounds of genome replication without cell division to generate polytene chromosomes containing up to 1000 copies of DNA per chromosome.

Question 12

J. Seiler in 1914 discovered which type of sex determination in moths?

Accepted Answer

C. ZZ - ZW — Even when two W chromosomes are paired to one Z chromosome in W 1W 2Z/ZZ systems, sex chromosome separation appears to be precise.

Question 13

Discontinuous variations in a population were first observed by:

Accepted Answer

A. Mendel — Mendel's concept of the gene was based on the analysis of hereditary variants—organisms that show identifiable and persistent differences for specific characters. He was the first to establish rules for the genetic analysis of such distinct variants.

Question 14

The genotype of blood group 'AB' in humans is _.

Accepted Answer

A. IA IB — ABO blood type in humans is determined by 3 alleles IA, IB (Dominant), and i (Recessive) Genotype IA shows blood group A. Genotype TB shows blood group B. Genotype Io shows blood group O. But, IA & IB are co-dominant alleles means neither of the dominant alleles can mask the expression of other dominant alleles. So, the genotype IA IB shows blood group AB.

Question 15

Which one is not a continuous trait?

Accepted Answer

B. Tongue rolling — A continuous trait displays a range of expression (such as weight, height, etc.) rather than an all-or-none appearance (such as white or red)

Question 16

Linked genes with closer loci _ Mendel’s law of independent assortment as they _ assort independently.

Accepted Answer

A. Don’t obey:cannot — Mendel's law of independent assortment states that the alleles of two (or more) different genes get sorted into gametes independently of one another

Question 17

Ahmed’s blood CANNOT clot properly; he was diagnosed with hemophilia A. He passed this trait to his grandson through his:

Accepted Answer

C. Daughter — X chromosome of the father is only transferred to the daughter, son takes the Y chromosome and haemophilia is a X-linked diseaseAhmed, who has hemophilia A, a condition where blood does not clot properly, can pass this trait to his grandson through his daughter. Hemophilia A is an X-linked recessive disorder, meaning that the gene responsible for the condition is located on the X chromosome.Since Ahmed is the grandfather, he must pass on his X chromosome to his daughter. If his daughter inherits the affected X chromosome from Ahmed, she becomes a carrier of hemophilia A. As a carrier, she has one normal X chromosome and one affected X chromosome, but since hemophilia A is a recessive trait, she does not show symptoms of the condition.When the daughter has a child (Ahmed's grandson), she has a 50% chance of passing on the affected X chromosome to her son. If the affected X chromosome is passed on, the grandson would inherit the hemophilia A trait and potentially experience clotting problems.It's important to note that if the daughter does not pass on the affected X chromosome to her son, he will not inherit hemophilia A. However, he would still be a carrier of the condition, meaning he could potentially pass it on to his own offspring if he has children in the future.

Question 18

A continuously varying trait is encoded by alleles of two or more different genes located at different loci, all influencing the same trait in an additive way is known as _.

Accepted Answer

B. Polygenes — Polygenic inheritance is a type of inheritance where a continuously varying trait is influenced by alleles of two or more different genes located at different loci. These alleles are said to be polygenes, and they all contribute to the phenotype of the individual in an additive way. Examples of traits that are controlled by polygenes include height, skin color, and intelligence.

Question 19

The total number of genes present in a particular population, at a particular time is called:

Accepted Answer

D. Gene Pool — Gene pool refers to the sum total of all the genes, alleles, and their variations present in a population at a particular time. It includes all the genetic information and diversity available within a population. The gene pool of a population is subject to change due to various factors such as mutation, migration, genetic drift, and natural selection.

Question 20

The type of gene interaction in which the effect caused by a gene at one locus interferes with the effect caused by another gene at another locus is known as:

Accepted Answer

B. Epistasis — Option A: Pleiotropy is a gene interaction in which a single gene affects multiple traits. Option B: The type of gene interaction in which the effect caused by a gene at one locus interferes with the effect caused by another gene at another locus is known as epistasis. Option C: Polygenic inheritance is a gene interaction in which multiple genes contribute to a single trait. Option D: Gene linkage is a phenomenon in which genes that are located close together on a chromosome are inherited together more often than would be expected by chance. Option E: Crossing over is a process that occurs during meiosis in which homologous chromosomes exchange genetic material.

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