1. Heredity and Variation
Mendelian
Inheritance
- Gregor Mendel
is known as the father of genetics for his work on pea plants.
- Principles of Inheritance:
- Law of Segregation: Alleles segregate during gamete formation.
- Law of Independent Assortment: Genes for different traits assort independently.
Deviations
from Mendelism
- Incomplete Dominance:
The phenotype of heterozygotes is intermediate between the phenotypes of
homozygotes (e.g., red and white flowers producing pink flowers).
- Co-dominance:
Both alleles in a heterozygote are fully expressed (e.g., AB blood type).
- Multiple Alleles:
More than two alleles exist for a gene (e.g., ABO blood groups).
- Pleiotropy:
A single gene affects multiple traits (e.g., sickle cell anemia affecting
blood, pain, and immunity).
- Polygenic Inheritance:
Multiple genes influence a trait, resulting in a continuous range of
phenotypes (e.g., skin color).
Chromosome
Theory of Inheritance
- Genes are located on chromosomes, which segregate and
assort independently during meiosis.
Sex
Determination
- In humans, sex is determined by the presence of XY
chromosomes (males) or XX chromosomes (females).
- In birds, the ZW system determines sex (ZW females, ZZ
males).
- In honey bees, sex is determined by the number of
chromosome sets (diploid females, haploid males).
Linkage
and Crossing Over
- Genes located close together on the same chromosome
tend to be inherited together (linkage).
- Crossing over during meiosis can result in genetic
recombination.
Sex-linked
Inheritance
- Traits linked to sex chromosomes; examples include:
- Haemophilia:
A blood clotting disorder linked to the X chromosome.
- Color Blindness:
A genetic condition affecting color perception, also X-linked.
Mendelian
Disorders in Humans
- Thalassemia:
A blood disorder caused by reduced hemoglobin production.
- Chromosomal Disorders:
- Down’s Syndrome:
Caused by trisomy of chromosome 21.
- Turner’s Syndrome: Affects females with a missing X chromosome (45,X).
- Klinefelter’s Syndrome: Affects males with an extra X chromosome (47,XXY).
2.
Molecular Basis of Inheritance
Search
for Genetic Material
- Early experiments indicated that DNA is the genetic
material, confirmed by studies such as those by Avery, MacLeod, and
McCarty.
Structure
of DNA and RNA
- DNA is a double helix composed of nucleotides (adenine,
thymine, cytosine, guanine), while RNA is single-stranded and contains
uracil instead of thymine.
DNA
Packaging
- DNA wraps around histone proteins to form nucleosomes,
which further coil to form chromatin.
DNA
Replication
- Semi-conservative process where each strand serves as a
template for a new complementary strand.
Central
Dogma
- Describes the flow of genetic information from DNA to
RNA to protein:
- Transcription: DNA → mRNA
- Translation: mRNA → Protein
Genetic
Code
- The sequence of nucleotides in mRNA is translated into
amino acids using codons.
Gene
Expression and Regulation
- The Lac Operon in E. coli serves as a model for
understanding gene regulation in prokaryotes.
Genome
and Human Genome Project
- The complete set of genetic material in an organism;
the Human Genome Project aimed to map all human genes.
DNA
Fingerprinting
- A technique used to identify individuals based on
unique patterns in their DNA.
3.
Evolution
Origin
of Life
- Theories about how life began on Earth include
abiogenesis and panspermia.
Biological
Evolution
- Change in the genetic composition of populations over
generations.
Evidence
for Biological Evolution:
- Paleontology:
Fossils show changes over time.
- Comparative Anatomy:
Homologous structures indicate common ancestry.
- Embryology:
Similar embryonic development suggests evolutionary relationships.
- Molecular Evidence:
Genetic similarities among species indicate evolutionary links.
Darwin’s
Contribution
- Proposed natural selection as the mechanism for
evolution; survival of the fittest leads to adaptation over time.
Modern
Synthetic Theory of Evolution
- Integrates Darwin's theory with genetics; emphasizes
mutation and gene flow as sources of variation.
Mechanisms
of Evolution
- Variation (Mutation and Recombination): Genetic
diversity arises from mutations and sexual reproduction.
- Natural Selection: Favorable traits increase an
organism's chances of survival and reproduction.
- Types:
- Stabilizing Selection: Favors
average traits.
- Directional Selection: Favors
one extreme phenotype.
- Disruptive Selection: Favors
both extreme phenotypes.
- Gene Flow: Movement of genes between populations
through migration.
- Genetic Drift: Random changes in allele frequencies due
to chance events.
Hardy-Weinberg
Principle
- Describes the conditions under which allele frequencies
remain constant in a population (no evolution occurs).
Adaptive
Radiation
- The diversification of a group of organisms into forms
filling different ecological niches.
Human
Evolution
- Study of how humans evolved from ancestral primates
through various stages, including bipedalism and increased brain size.
Key
Diagrams
- Structure of DNA showing nucleotide components.
- Diagram illustrating Mendelian inheritance patterns.
- Phylogenetic tree showing evolutionary relationships
among species.
Summary
This unit covers fundamental
concepts in genetics and evolution:
- Heredity involves Mendelian principles and deviations
such as co-dominance and polygenic inheritance.
- Molecular genetics explains DNA structure, replication,
transcription, translation, and gene regulation mechanisms.
- Evolutionary biology discusses evidence supporting
evolution, mechanisms like natural selection, genetic drift, and human
evolution processes.
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