Question:

Explain the following terms with example (a) Co-dominance (b) Incomplete dominance

Answer:

a) Co-dominance: Co-dominance is a form of genetic expression in which both alleles of a gene are expressed simultaneously in the phenotype of an organism. For example, in the AB blood group, both the A and B alleles are expressed and the individual has both the A and B antigens on their red blood cells.

b) Incomplete Dominance: Incomplete dominance is a form of genetic expression in which one allele of a gene is not completely dominant over the other allele. As a result, the phenotype of the organism is a blend of the two alleles. For example, in snapdragons, the red allele is not completely dominant over the white allele, so the result is a pink flower.

Question:

Briefly mention the contribution of T.H. Morgan in genetics.

Answer:

1. T.H. Morgan was an American geneticist who made significant contributions to the field of genetics.

2. He is best known for his work on the fruit fly, which he used to develop the concept of the gene, as well as his work on sex-linked inheritance, chromosome mapping, and mutation.

3. He was the first to identify the concept of the gene as a unit of heredity, and he developed the idea of the chromosome theory of inheritance.

4. He also developed the concept of linkage and was the first to map a gene to a specific chromosome.

5. His work provided the foundation for modern genetics and helped to establish the field as a legitimate scientific discipline.

Question:

Define and design a test-cross.

Answer:

Step 1: Define the purpose of the test-cross. The purpose of a test-cross is to determine the genotype of an organism when its phenotype is known.

Step 2: Design the test-cross. To design the test-cross, select an organism with the same phenotype as the organism whose genotype is being determined. Cross the two organisms together, and the genotype of the organism of interest can be determined by analyzing the offspring of the cross.

Question:

Two heterozygous parents are crossed. If the two loci are linked what would be the distribution of phenotypic features in F1​ generation for a dibybrid cross?

Answer:

Step 1: Determine the genotypes of the two heterozygous parents. For example, the two parents may be AaBb and AaBb.

Step 2: Calculate the Punnett Square for the dibybrid cross. The Punnett Square will show the different combinations of alleles that can be produced from the two parents.

Step 3: Determine the phenotypic features of the F1 generation. Each combination of alleles will produce a different phenotype. For example, if the two parents are AaBb and AaBb, the F1 generation will have the phenotypes AABB, AAbb, aaBB, and aabb.

Question:

Using a Punnett Square, workout the distribution of phenotypic features in the first filial generation after a cross between a homozygous female and a heterozygous male for a single locus.

Answer:

1. Draw a Punnett square.

2. Place the alleles of the female in the left column of the Punnett square.

3. Place the alleles of the male in the top row of the Punnett square.

4. Fill in the Punnett square with the alleles from the female and male.

5. Determine the distribution of phenotypic features in the first filial generation by looking at the combinations of alleles in the Punnett square.

Question:

How is sex determined in human beings?

Answer:

1. Sex in human beings is determined by the presence or absence of certain chromosomes.
2. Females typically have two X chromosomes (XX), while males typically have one X chromosome and one Y chromosome (XY).
3. The presence of the Y chromosome triggers the development of male characteristics, while the absence of the Y chromosome results in the development of female characteristics.
4. Genes on the Y chromosome are responsible for the production of hormones that cause male characteristics to develop, such as the development of male reproductive organs.

Question:

A diploid organism is heterozygous for 4 loci, how many types of gametes can be produced?

Answer:

Answer:

1. A diploid organism has two sets of chromosomes, one from each parent.
2. Heterozygous means that the organism has two different alleles (variations of a gene) at each of the four loci.
3. Since there are two alleles at each locus, there are two possible combinations of alleles that can be present in a gamete.
4. Therefore, there are 2^4 (or 16) possible types of gametes that can be produced.

Question:

Explain the Law of Dominance using a monohybrid cross.

Answer:

1. The Law of Dominance states that when two alleles of a gene are present, one is expressed while the other is not expressed.

2. A monohybrid cross is a cross between two individuals that differ in one trait.

3. To explain the Law of Dominance using a monohybrid cross, we can look at the Punnett Square. In the Punnett Square, two alleles of a gene are represented by letters such as A and a. The capital letter represents the dominant allele and the lowercase letter represents the recessive allele.

4. When the two alleles are paired together, the dominant allele will be expressed and the recessive allele will not be expressed. This is known as the Law of Dominance.

5. For example, if the two alleles are A and a, then the phenotype of the offspring will be A. This is because the A allele is dominant and will be expressed in the offspring, while the a allele is recessive and will not be expressed.

Question:

What is point mutation? Give one example.

Answer:

Answer: Point mutation is a type of genetic mutation in which a single nucleotide base in a gene sequence is changed. An example of point mutation is a change in the DNA sequence from ATCG to ATGG, which changes the codon from encoding the amino acid leucine to encoding the amino acid tryptophan.

Question:

A child has blood group O. If the father has blood group A and mother blood group B, work out the genotypes of the parents and the possible genotypes of the other offsprings.

Answer:

1. The father’s genotype is IAIA and the mother’s genotype is IBIB.

2. The child’s genotype is IAIB, which is a combination of the father’s IAIA and the mother’s IBIB.

3. The possible genotypes of the other offsprings are IAIA, IAIB, IBIB, and II.

Question:

Who had proposed the chromosomal theory of the inheritance?

Answer:

1. The chromosomal theory of inheritance was proposed by the scientist, Gregor Mendel.

Question:

What is pedigree analysis? Suggest how such an analysis can be useful.

Answer:

Answer: Pedigree analysis is a method of tracing a family’s genetic lineage and medical history. It is used to identify inherited genetic disorders and to assess the risk of passing on a genetic disorder to future generations.

Pedigree analysis can be useful in a variety of ways. For example, it can be used to identify whether a person is at risk of inheriting a genetic disorder, or to identify the source of a genetic disorder in a family. It can also be used to predict the likelihood of a particular trait being passed on to future generations. Additionally, it can be used to gain insight into the genetic makeup of a family, and to help identify potential treatments for genetic disorders.

Question:

When a cross is made between a tall plant with yellow seeds (TtYy) and a tall plant with the green seed (Ttyy), what proportions of phenotype in the offspring could be expected to be (a) tall and green. (b) dwarf and green.

Answer:

a) Tall and green: 3/4 or 75%

b) Dwarf and green: 1/4 or 25%

Question:

Mention any two autosomal genetic disorders with their symptoms.

Answer:

1. Down Syndrome: Symptoms include low muscle tone, small stature, an upward slant to the eyes, and a single deep crease across the center of the palm.

2. Turner Syndrome: Symptoms include short stature, webbed neck, low hairline at the back of the neck, broad chest, and infertility.

Question:

Differentiate between the following (a) Dominance and Recessive (b) Homozygous and Hetrozygous (c) Monohybrid and Dihybrid.

Answer:

(a) Dominance: Dominance is a relationship between two alleles of a gene, where one allele masks the expression of the other.

Recessive: Recessive is a relationship between two alleles of a gene, where the expression of one allele is not masked by the other allele.

(b) Homozygous: Homozygous is a type of genetic inheritance where both alleles of a gene are the same.

Heterozygous: Heterozygous is a type of genetic inheritance where the two alleles of a gene are different.

(c) Monohybrid: Monohybrid is a type of genetic inheritance that involves the inheritance of a single trait.

Dihybrid: Dihybrid is a type of genetic inheritance that involves the inheritance of two traits.