Genetics: DNA Structure

Study Notes

Genetics Overview

Genetics explores heredity and the transmission of characteristics from parents to offspring.
Essential for fields like medicine, agriculture, and biotechnology.

DNA Structure

DNA (deoxyribonucleic acid) is a double helix made of two strands.
Basic unit: nucleotide, consisting of:
- Phosphate group
- Deoxyribose sugar
- Nitrogenous base (A, T, C, G)
Sequence of nitrogenous bases encodes genetic information; complementary base pairing (A-T, C-G) is vital for replication.

Genes and Chromosomes

A gene is a nucleotide sequence that codes for proteins or functional RNA.
Chromosomes are thread-like structures in eukaryotic cell nuclei, humans have 46 (23 pairs), inherited equally from both parents.

Alleles and Genotypes

Alleles are different forms of a gene leading to varied phenotypic effects.
Genotypes refer to the specific alleles possessed by an organism.
Types of genotypes:
- Homozygous: Two identical alleles (e.g., RR, rr).
- Heterozygous: Two different alleles (e.g., Rr).

Phenotypes and Phenotypic Ratios

Phenotype represents observable traits influenced by genotype and environment.
Dominance governs phenotypic expression:
- Dominant alleles mask recessive alleles (e.g., Rr shows red).
- Recessive alleles are expressed only with two copies (e.g., rr is white).
In a monohybrid cross (Rr x Rr), the expected phenotypic ratio is 3:1 (dominant to recessive).

Mendel's Laws of Inheritance

Law of Segregation: Alleles segregate during gamete formation, each gamete has one allele per trait.
Law of Independent Assortment: Alleles for different traits assort independently during gamete formation.

Inheritance Patterns

Dominant Inheritance: Traits expressed with one dominant allele (e.g., Huntington's disease).
Recessive Inheritance: Traits expressed with two recessive alleles (e.g., cystic fibrosis).
X-Linked Inheritance: Traits on the X chromosome often affect males more (e.g., hemophilia).

Genetic Variation

Results from mutations, gene flow, and sexual reproduction:
- Mutations: Changes in DNA can create new alleles.
- Gene Flow: Movement of genes enhances diversity in populations.
- Sexual Reproduction: Introduces variation through meiosis and fertilization.

Applications of Genetics

Medicine: Facilitates diagnosis and treatment of genetic disorders.
Agriculture: Involves selective breeding to improve crops and livestock traits.
Gene Therapy: Techniques developed to correct defective genes for genetic disorder treatment.

Conclusion

Genetics provides insights into biological processes of life, promoting advances in health and agriculture.

Description

Explore the fascinating field of genetics, focusing on DNA structure and its role in heredity. Learn how traits are transmitted from parents to offspring and the significance of this knowledge in medicine, agriculture, and biotechnology. This quiz will enhance your understanding of the molecular blueprint of life.