Heredity -2 - Class 10 MCQ

Sexual Reproduction:

• Involves the combination of genetic material from two parents.
• Each parent contributes half of the genetic material, resulting in offspring with a unique mix of genes.
• This genetic recombination increases variation and diversity among offspring.

Asexual Reproduction:

• Involves a single parent and produces genetically identical offspring, known as clones.
• Does not lead to genetic variation apart from occasional mutations.
• More genetic variation occurs through sexual reproduction, making it the correct answer.

• Heredity refers to the transfer of genetic characteristics from parents to their offspring.
• This process occurs through genes, which are units of heredity located on chromosomes.
• Offspring inherit these genes during reproduction, receiving a mix from both parents.
• Heredity is responsible for traits such as eye color, hair type, and even certain behaviors or susceptibilities to diseases.
• This transfer ensures continuity of genetic information across generations, enabling species to adapt and evolve over time.

- Genes passed down from the parents:

• Genes are segments of DNA that carry the instructions for the development, functioning, and reproduction of organisms.
• They determine specific traits by encoding proteins that affect the organism's structure and processes.
• Traits such as eye color, blood type, and certain inherited diseases are directly influenced by genetic information.
• Inheritance follows Mendelian genetics, where traits are passed from parents to offspring through alleles.

• Gregor Mendel is known as the father of genetics.
• He conducted experiments with pea plants.
• He discovered that traits are passed from parents to offspring through discrete units, now known as genes.
• Mendel identified dominant and recessive traits.
• Dominant traits mask recessive traits in offspring when both are present.
• Mendel's work laid the foundation for understanding inheritance patterns.
• His principles: Law of Segregation and Law of Independent Assortment are fundamental to genetics.

• Gregor Mendel, known as the father of genetics, studied the inheritance of traits in pea plants.
• He observed that when crossing two heterozygous parents (F1 generation) for a single trait, the F2 generation showed a 3:1 phenotypic ratio.
• This means 3 offspring displayed the dominant trait, while 1 displayed the recessive.
• This ratio results from the combination of alleles: 1 homozygous dominant (AA), 2 heterozygous (Aa), and 1 homozygous recessive (aa).

• Chromosomes from Parents: Human sex determination is based on the chromosomes inherited from parents. Each parent contributes one sex chromosome.
• Chromosome Pairs: Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).
• Role of Y Chromosome: The presence of a Y chromosome determines male development because it carries the SRY gene, which triggers male characteristics.
• Genetic Basis: The combination of these chromosomes at fertilization determines the sex of the offspring.

In Mendel's experiments, the F2 generation for a single trait resulted from crossing two F1 heterozygous individuals (e.g., Tt x Tt). The genotypic ratio for the F2 generation is: - 1:2:1

This ratio represents:
- 1 homozygous dominant (TT)
- 2 heterozygous (Tt)
- 1 homozygous recessive (tt)

This occurs due to the combination of alleles, where each parent contributes one allele, resulting in the possible combinations of TT, Tt, and tt.

• Gregor Mendel's experiments with pea plants established foundational principles of inheritance.
• He focused on traits like seed shape, seed color, and plant height.
• Mendel discovered that certain traits were dominant and others were recessive.
• In his experiments, the round seed shape consistently appeared in the F1 generation when crossing pure-bred round and wrinkled seeds.
• Thus, the round seed shape is dominant, while the wrinkled seed shape is recessive.
• Therefore, B: Round seed shape is the correct answer.

Variations during reproduction primarily occur through:

• Genetic Recombination: During sexual reproduction, chromosomes from both parents exchange genetic material, creating unique combinations in offspring.
• Mutations: Random changes in the DNA sequence can lead to new traits, introducing variations across generations.

These processes ensure diversity within a species, aiding in adaptation and survival. Genetic inheritance alone does not account for new variations, making option B the correct answer.

• Sex Chromosomes in Humans: Humans have 23 pairs of chromosomes, with one pair being the sex chromosomes.
• Female Chromosomes: Females have two X chromosomes, represented as XX. This combination does not contain a Y chromosome.
• Male Chromosomes: Males have one X and one Y chromosome, represented as XY. This combination determines male characteristics.
• Sex Determination: The presence of the Y chromosome is crucial for male development, making sex chromosomes essential for sex determination in humans.
• Thus, option C is correct.