Unscramble the 30 Terms from the Bug and send your answers in the comments column or in telegram.
Fill in the Blanks
- The transmission of characters from parent to offspring is known as __.
- The study of heredity and variations is called __.
- Organisms that are carbon copies of one another are known as __.
- Variation in sexually reproducing organisms is caused due to factors like environment, _, and _ of genes, and __.
- The first study of inheritance was conducted by _ on the _ plant.
- The paired condition of chromosomes is termed as __.
- The unpaired condition of chromosomes is termed as __.
- The genetic material in all organisms is _ for DNA and _ for RNA.
- Mendel’s laws of inheritance include:
- __
- __
- __
- The genetic composition of an organism is called its _, while the visible characteristics are called its _.
- The offspring resulting from the cross of two parents is termed as the __ generation.
- When the F1 generation breeds among themselves, the resulting offspring are called the __ generation.
- Mendel used the _ plant for his experiments and studied contrasting traits like _ seeds, _ plants, and _ flowers.
Key
Here are the answers (key) for the fill-in-the-blank questions:
- Heredity
- Genetics
- Clones
- Crossing over, recombination, mutation
- Gregor Mendel, garden pea
- Diploid
- Haploid
- Deoxyribonucleic Acid (DNA), Ribonucleic Acid (RNA)
- Mendel’s laws of inheritance include:
- Law of Dominance
- Law of Segregation
- Law of Independent Assortment
- Genotype, Phenotype
- F1 (First Filial)
- F2 (Second Filial)
- Garden pea (Pisum sativum), round/wrinkled, tall/short, white/violet
Fill the Missing Words
5. During Monohybrid Cross
- When tall pea plants are crossed with short pea plants then in F1 generation only tall plants were obtained.
- F2 progeny of F1 tall plants are not all tall but one quarter of them are short indicating that both tallness and shortness traits were inherited in F1 but only tallness trait was expressed due to dominance.
- In dihybrid cross two pairs of contrasting characters were considered. Tall plant with round seeds were crossed with short plant with wrinkled seeds. In F1 tall plants with round seeds were obtained. On selfing these F1 plants with F2 produced tall plants with round seeds, short plant with wrinkled seeds and some new combinations (tall plant with wrinkled seeds and short plant with round seeds) were also obtained. The tall/short trait and round wrinkled traits are independently inherited.
- The expression of a particular trait is controlled by gene.
6. DNA is the source of making protein in a cell.
The section of DNA that provides information for one protein is called gene.
7. Physical and Chemical Basis of Heredity
Mendel (1866) said that heredity was controlled by particles, called germinal units, or factors.
8 Sex determination is the process by which the sex of a person is determined.
All human chromosomes are not paired. 22 pairs are called autosomes. Women have a perfect pair of sex chromosomes XX. But men have a mismatched pair XY.
Heredity and Rules of Inheritance
1. Introduction to Heredity
- Heredity is the process through which traits and characteristics are passed from parents to their offspring.
- The study of heredity and variations among organisms is known as genetics.
- Traits are specific characteristics (e.g., eye color, height, etc.) that are inherited through genes.
- The genetic material in all organisms is DNA (Deoxyribonucleic Acid), while RNA (Ribonucleic Acid) assists in protein synthesis.
2. Basics of Inherited Traits
- Genes are units of heredity that determine specific traits and are located on chromosomes.
- Each organism inherits two alleles for each trait, one from each parent. Alleles can be dominant or recessive.
- Dominant alleles express their traits even if only one allele is present (symbolized by uppercase letters, e.g., T for tall).
- Recessive alleles express their traits only when both alleles are recessive (symbolized by lowercase letters, e.g., t for short).
- Genotype refers to the genetic makeup of an organism, while phenotype refers to the observable characteristics.
3. Mendel’s Contributions to Genetics
- Gregor Mendel is known as the “Father of Genetics” due to his pioneering work on the inheritance of traits in pea plants.
- Mendel conducted experiments on Pisum sativum (garden pea), focusing on specific traits such as plant height, seed shape, and flower color.
- His work established the foundational laws of inheritance:
- Law of Dominance: In a heterozygous pair of alleles, the dominant allele masks the expression of the recessive allele.
- Law of Segregation: During the formation of gametes, the two alleles for a trait separate, and each gamete receives only one allele.
- Law of Independent Assortment: Alleles for different traits are distributed to gametes independently, allowing new combinations in offspring.
4. Dominant and Recessive Traits
- Dominant Traits: Traits that appear in the F1 generation when two organisms with contrasting traits are crossed (e.g., tallness in pea plants).
- Recessive Traits: Traits that are masked in the F1 generation and reappear in the F2 generation when two heterozygous individuals are crossed.
- For example, in Mendel’s pea plants:
- Tallness (T) is dominant over shortness (t).
- Round seed shape (R) is dominant over wrinkled shape (r).
5. Mendelian Experiments and Inheritance Patterns
- Monohybrid Cross: A cross between two organisms with different alleles for one trait.
- When Mendel crossed a tall plant (TT) with a short plant (tt), all F1 offspring were tall (Tt).
- When F1 plants (Tt) were self-crossed, the F2 generation exhibited a 3:1 ratio of tall to short plants, confirming that the recessive trait had been masked in F1.
- Dihybrid Cross: A cross between two organisms with different alleles for two traits.
- Mendel crossed plants with round yellow seeds (RRYY) and wrinkled green seeds (rryy).
- The F1 generation had round yellow seeds (RrYy), showing the dominant traits.
- Upon self-crossing F1 plants, the F2 generation showed a 9:3:3:1 ratio of the phenotypes: round yellow, round green, wrinkled yellow, and wrinkled green, illustrating the Law of Independent Assortment.
6. Independent Assortment and Expression of Traits
- Independent Assortment: Alleles of different genes are distributed independently of one another during gamete formation.
- This principle leads to genetic variation as it allows for different combinations of traits.
- Mendel observed that traits such as height and seed shape were inherited independently, meaning that a tall plant could have either round or wrinkled seeds.
- The independent expression of traits provides the basis for genetic diversity in sexually reproducing organisms.
7. F1 and F2 Generations
- F1 Generation (First Filial Generation): The first generation of offspring resulting from a cross between two parent organisms with different traits. In Mendel’s experiments, the F1 generation displayed only the dominant trait.
- F2 Generation (Second Filial Generation): The offspring resulting from a self-cross of F1 individuals. Mendel observed a reappearance of the recessive trait in the F2 generation, typically in a 3:1 ratio in monohybrid crosses and a 9:3:3:1 ratio in dihybrid crosses.
8. Significance of Mendel’s Work
- Mendel’s principles provided the first scientific explanation of inheritance patterns.
- His work laid the foundation for the field of genetics, explaining how traits are passed on, which helped in understanding genetic disorders, selective breeding, and genetic engineering.
Summary
- Heredity is the transfer of traits from parents to offspring.
- Dominant alleles mask the effects of recessive alleles in heterozygous organisms.
- Mendel’s laws of inheritance (dominance, segregation, and independent assortment) describe how traits are passed down through generations.
- Mendelian experiments using monohybrid and dihybrid crosses revealed predictable patterns in trait inheritance, leading to ratios that showcase dominant and recessive traits.
- Independent assortment during gamete formation increases genetic variation, a fundamental principle in evolutionary biology.
