Inheritance and Genetic Variation
This page covers the fundamental concepts of inheritance patterns and mechanisms of genetic variation, including Mendel's law of inheritance, types of dominance, and processes that contribute to genetic diversity.
Mendel's Laws of Inheritance
Gregor Mendel established three key principles that form the foundation of genetic inheritance:
-
Law of Segregation: During gamete formation, the two alleles for each gene separate, ensuring that each gamete carries only one allele for each gene.
-
Law of Independent Assortment: The segregation of alleles for one gene occurs independently of other genes, leading to the random assortment of chromosomes during meiosis.
-
Law of Dominance: In heterozygous individuals, the dominant allele will mask the expression of the recessive allele in the phenotype.
Highlight: These laws explain how genetic traits are passed from parents to offspring and form the basis of modern genetics.
Types of Dominance
The page discusses two main types of dominance:
-
Complete Dominance:
- Most common inheritance pattern
- Dominant allele (represented by a capital letter) completely masks the recessive allele (lowercase letter)
- Examples of genotypes: BB, Bb, bb
-
Co-dominance:
- Both alleles are expressed equally in the phenotype
- Example: Feathering in chickens - Black [B], White [W], Speckled Coat [B/W]
Example: In chicken feather color, black (B) and white (W) alleles can be co-dominant, resulting in a speckled coat (B/W) when both alleles are present.
Crossing Over
The page explains the process of crossing over:
- Occurs during prophase I of meiosis
- Homologous chromosomes pair up
- Genetic material is exchanged between non-sister chromatids
- Contributes to genetic variation
Definition: Crossing over is the exchange of genetic material between homologous chromosomes during meiosis, which increases genetic diversity in offspring.
Zygosity
The concept of zygosity is introduced:
- Gametes are haploid, containing one allele for each gene
- Zygotes formed after fertilization contain two alleles for each gene
- Homozygous: maternal and paternal alleles are the same
- Heterozygous: maternal and paternal alleles are different
Vocabulary: Zygosity refers to the genetic similarity of alleles for a trait in an organism.
Practical Application
The page concludes with an example problem:
Parents: Rr x rr
Gametes: R or r × r
Key: R - round, r - wrinkled
Chances: 50% round, 50% wrinkled
Ratio: 1:1
Example: This problem demonstrates how to predict offspring phenotypes based on parental genotypes using Mendel's law of inheritance.
The page effectively covers the core concepts of Mendel's law of inheritance, types of dominance, and mechanisms of genetic variation, providing a comprehensive overview of basic genetics principles.
