Genetics: Heredity and Variation

• Genetics is the study of heredity and variation

Heredity/Inheritance

• It is the reliable transmission of traits.

Variation/Diversity

• It is the degree of difference in traits among parents and offspring.

Somatic Variation

• Occurs in somatic cells.
• Not transferred to the next generation.
• Does not contribute to evolution.
• Acquired traits e.g. piercing ears, cutting dogs tails

Gametic Variation

• Occurs in reproductive cells.
• Transferred to the next generation.
• Important for evolution.
• Inherited traits e.g. hair color, height.

Variation During Reproduction

• Variations are reflected by reproduction, be it sexual or asexual.

Asexual Reproduction

• Fewer variations.
• Caused by minor errors during DNA replication.

Sexual Reproduction

• More diversity.
• Due to cross-breeding, chromosome segregation, and mutations.

Advantages of Variation

• Diversity allows organisms to adapt to different environments.
• Tolerance example: organisms better able to survive heat
• Selection of beneficial variations drives evolution.
• Example: free vs attached earlobes.

Mendel's Contributions

• Mendel presented the primary laws of heredity.
• Also known as the "father of genetics."
• Studied traits in pea plants, observing 7 contrasting characteristics.

Traits Studied by Mendel

• Seed shape: round or wrinkled.
• Seed color: yellow or green.
• Flower color: purple or white.
• Pod shape: inflated or constricted.
• Pod color: green or yellow.
• Flower position: axial or, terminal.
• Plant height: tall or dwarf.

Why Mendel Chose Pea Plants

• Traits easily visible.
• Short life cycle.
• Self-pollinating, but can also be cross-pollinated artificially.
• Produces many seeds in a single generation.

Mendel's Experiment: Contrasting Traits

• Mendel studied 7 pairs of contrasting traits in pea plants.

Monohybrid Cross

• Cross between two pea plants with one pair of contrasting traits.
• Example: Crossing tall and dwarf plants.
• All plants in the F1 generation were found to be tall
• 3/4 of the F2 generation were tall and 1/4 were dwarf.
• Phenotype ratio in F2 = 3:1 (3 tall plants: 1 dwarf plant)
• Genotype ratio F3 = 1:2:1.
• TT, Tt, and tt had a ratio of 1:2:1.
• TT and Tt are tall, while tt is a dwarf plant in this case.
• Therefore, one copy of T is enough to make the plant tall
• The presence of two copies of t i.e. tt are required for the plant to be a dwarf.
• Dominant traits example- T and recessive example - t.

Dihybrid Cross

• A cross between two plants with two pairs of contrasting traits.
• Example- seed color (yellow or green) and seed shape (round or wrinkled) in pea plants.
• In this case independent assortment of traits is observed (seed color and, seed shape).
• Phenotype ratio of 9 round yellow : 3 round green : 3 wrinkled yellow : 1 wrinkled green were observed

How Traits Express Themselves

• Genes Provide Instructions To make Proteins
• DNA in the cell -> Gene (functional unit of DNA) -> Information Source -> Protein Synthesis
• Proteins determine traits (enzymes and hormones).
• Example: Enzyme efficiency

Sex Determination

• Factors responsible for sex determination.
• In some animals, it depends on incubation temperature of eggs.
• Snails are the said example.
• Some organisms like humans, sex depends on sex chromosomes i.e. XX (female) and XY (male).

Sex Determination in Humans

• Sex chromosomes: male (XY), female (XX)
• Half the children will be boys and half girls. All children get an X chromosome from their mothers.
• A child's sex depends on what type of chromosome they get from the father.
• If a child inherits the X chromosome from their father, they will be a girl. If they inherited a Y, the child will be a boy.

Evolution

• Gradual process that happened over millions of years and where new species originated.

Situation 1

• Group of red beetles - variation in color by reproduction.

Summary of Situation 1

• Green beetles gain advantage from natural selection because they are hidden in green bushes
• This resulted in adaptation in the beetle community and better survival in the environment.

Situation 2

• Group of red beetles
• Variation by reproduction - mutation in color (blue).
• Then the elephant trampled the beetles
• It was coincidental the blue beetles survived. – Color change did not ensure better survival.

Situation 3

• Group of red beetles
• Plant disease in the habitat.
• Beetle population and size decrease due to malnutrition.
• Plant disease ends.. Beetle population/size increases
• There was an environmental effect on population, not a genetic change.

Acquired And Inherited Traits

• Acquired traits are gained during an organism's lifetime/inherited traits are passed via genes.
• Acquired traits do not change DNA/inherited traits pass through offspring.
• Acquired traits can’t lead to evolution/inherited traits support evolution.

Speciation

• Arises from Isolation and Accumulation of Changes
• Gene Flow - When populations are not completely isolated, it can occur between them. Genetic Drift - Random gene drifts in an isolated population cause evolution.
• Natural Selection - Organisms with better features adapt better.
• Geographical Isolation - Populations cannot interbreed because of factors like river, mountains etc.
• Over time populations become unable to interbreed - new species.

Evolutionary Relationship Scheme

• Homologous characteristics - Similar morphology but dissimilar function.
• Example: Vertebrate Limbs (wings, arms, legs etc.)
• Analogous characteristics - Dissimilar morphology but similar function.
• Example: Wings of bats and birds
• Fossils - Preserved remains of organisms and act as evidence for evolution.
• Example: Ammonite, Trilobite, Nautilus, Rajosaurus

Fossil Dating

• Relative dating - fossils near the surface are more recent than those deeper down.
• Absolute dating (radioactive dating) - determines the age of fossils

Evolution And Classification

• The two are related as classification is a reflection of evolutionary relationships.
• The higher the common features between 2 species, the closer their relationship.

Stages of Development

• Evolution happens in generations.
• If have suitability, gain benefit from it.
• Eye Development - Complex organs don't evolve from single DNA changes - it happens in stages. Small simple eyes (Planaria) to complex eyes (insects) to binocular vision (Man).

Quality Benefit

• Wings (Feathers) - Evolved for insulation but later became useful in flying.
• Ex. Dinosaurs had feathers but could not fly, birds later adapted feathers for flight.

Artificial Selection

• Two thousand years ago, man, in the form of food plants, cultivated wild cabbage and through selection developed various vegetables, called artificial selection.

Molecular Phylogeny

• Idea that DNA changes during reproduction are essential to development. (ii) The changes in the DNA of more distant related mammals will be stored in greater numbers.

Human Evolution

• Human Development Research Methods
• Excavation, Time Determination, DNA Sequencing, Fossil Studies

Genetics Definitions

• Genes - Mendel called genes 'factors'. Genes are the units of inheritance.
• Alleles - Alternative contrasting traits i.e alleles, which are variations of a gene.
• Heterozygous - Organisms with dissimilar characters i.e Tt.
• Homozygous - Organisms with single trait alleles that are equal i.e. TT, tt.
• Prevalence (Dominance) - Gene is only in F1 that is visible.
• Non-Prevalence (Recessive) - a gene that is not apparent in the presence of a dominant gene.
• Gene Type (Genotype) - The gene is the basis for the appearance i.e. TT or tt.
• Visual Type (Phenotype) - A type based on the external appearance of the organism: tall plants, dwarf plants.
• Micro Evolution - Evolution in small areas, for example- color changes in the beetle's body color.
• Species - a group of similar organisms in the population that copulate with each other and produce productive organisms.
• Chromosomes - Thread-like structures found in the center of the cell, which contains the genetic information of the cell.
• DNA - Deoxy-ribose nucleic acid, which is present in the chromosome