Introduction to Heredity and Mendelian Genetics

Study Notes

Introduction to Heredity

Heredity is the passing of traits from parents to offspring.
Traits are determined by genes, which are segments of DNA.
Genes provide instructions for building and maintaining an organism.
Inheritance involves complex mechanisms.

Mendelian Genetics

Gregor Mendel's pea plant experiments formed the basis for understanding inheritance.
He observed predictable inheritance patterns for traits.
Mendel's laws are fundamental principles of inheritance:
- Law of Segregation: Each parent contributes one allele for each trait to offspring, separating alleles during gamete formation.
- Law of Independent Assortment: Traits are inherited independently of each other.
Alleles are different versions of a gene.
Dominant alleles mask recessive alleles.
Genotype is the genetic makeup (e.g., AA, Aa, aa).
Phenotype is the observable physical trait (e.g., purple flowers, white flowers).

Beyond Mendelian Genetics

Not all traits follow simple Mendelian patterns.
Incomplete dominance: Heterozygotes show an intermediate phenotype between the two homozygous phenotypes.
Codominance: Both alleles are expressed in the heterozygote, showing traits from both (e.g., AB blood type).
Multiple alleles: More than two alleles for a gene exist in a population, resulting in more than two genotypes.
Polygenic inheritance: Multiple genes influence a single trait, creating a wide range of phenotypes (e.g., height, skin color).
Pleiotropy: A single gene affects multiple traits, causing complex interactions.

Chromosomes and Gene Expression

Chromosomes are thread-like DNA structures.
Humans have 23 pairs of chromosomes (22 autosomes, 1 sex chromosome).
Genes are located at specific positions (loci) on chromosomes.
Gene expression is tightly regulated, controlled by processes dictating when and how genes are used.
Environmental factors affect gene expression, influencing phenotypes.
Epigenetics studies heritable changes in gene expression without altering the DNA sequence.

Sex-Linked Inheritance

Sex-linked genes are located on sex chromosomes (X and Y).
Sex-linked traits show different inheritance patterns in males and females due to X chromosome presence/absence.
Color blindness and hemophilia are examples of sex-linked traits.

Genetic Disorders

Mutations in DNA lead to genetic disorders.
Disorders can arise from single gene changes (e.g., cystic fibrosis) or chromosomal abnormalities (e.g., Down syndrome).
Genetic counseling provides information and support to families affected by or at risk of genetic disorders.

Modern Techniques in Genetics

Advances in molecular biology offer powerful gene and inheritance study tools.
Techniques like PCR, DNA sequencing, and genetic engineering are revolutionizing research and leading to new medical applications (e.g., genetic testing).

Description

Explore the fundamental concepts of heredity and Mendelian genetics. This quiz covers the passing of traits, the significance of genes, and the laws of inheritance established by Gregor Mendel. Test your understanding of these essential biological principles.