Study Notes on Genes and Inheritance

Chromosomes: Threads located in the nucleus of every cell.
- Discovered in the 19th century due to advancements in microscope technology.
- Require special stains for visibility.
Types of Cells:
- Human cells: 46 chromosomes.
- Fruit fly cells: 8 chromosomes.
- Mango tree cells: 40 chromosomes.
Chromosome Numbering:
- Chromosomes are numbered based on length; longest is chromosome 1, second longest is chromosome 2, etc.
- One of the chromosomes is the sex chromosome pair.
- Each chromosome appears as a cross shape before cell division due to duplication.

Why can we usually not see chromosomes?
- Because they are not typically condensed enough to be visible, even under a microscope.
Do red blood cells contain chromosomes?
- No, they do not contain a nucleus; hence, they do not contain chromosomes.

Definition of Genes: Portions of chromosomes that control specific traits in an organism; each chromosome contains hundreds of genes arranged in a sequence.
- Example: Genes on chromosome 15 are responsible for eye color in humans.
Composition of Chromosomes:
- Chromosomes consist of DNA.
- DNA has a double helix structure, similar to a twisted ladder; one gene can be 2,500 twists long.

Difference between a chromosome and a gene?
- A chromosome is a structure housing many genes, while a gene is a specific sequence that codes for a trait.
Variation in fruit fly wing shapes?
- Variations in genes lead to different physical characteristics; environmental factors may also play a role.

Gametes: Specialized cells for reproduction.
- Male gametes: sperm cells.
- Female gametes: egg cells.
Formation of a New Cell:
- Sperm cells (23 chromosomes) unite with egg cells (23 chromosomes) to form a zygote with 46 chromosomes.

Sperm Cell: 0.01 mm to 0.05 mm, contains nucleus with genetic material from the father, has a tail for rapid movement.
Egg Cell (Ovum): 0.1 mm, contains nucleus with genetic material from the mother and cytoplasm providing nutrients for embryo development, covered by a jelly layer for protection.

What is a gamete?
- A gamete is a specialized reproductive cell (either sperm or egg).
Comparison table between sperm cell and egg cell:
- Sperm cell: Tail for movement, smaller size.
- Egg cell: Larger size, contains protective jelly layer.

Sperm deposited in the vagina swim into the oviduct to meet the egg.
Upon successful entry, a jelly layer around the egg prevents additional sperm from entering.
The fusing of sperm and egg is called fertilization; leads to the formation of a zygote.
The zygote divides repeatedly, ultimately developing into a fully formed organism.

Chromosomes that determine genetics: XX for female, XY for male. One chromosome set from each parent.
Every egg cell has one X chromosome; sperm may carry either X or Y.
- If X from sperm, the zygote is female (XX). If Y, the zygote is male (XY).

Who determines the sex of the baby?
- The father determines the sex; the mother only provides an X chromosome.
Explain equal sex ratio at birth.
- Approximately equal numbers of X and Y sperm lead to an equal number of female and male births.

Inheritance: The passing of DNA and associated characteristics from parents to offspring.
Definition of Variation: Differences within species due to both genetic and environmental factors.
Example: Kidney vetch with flowers showing multiple colors; example of studied flower variation and results recorded in a bar chart.

Genetic and environmental factors contribute to individual differences.
Each gamete carries half the genetic information, leading to unique offspring upon fertilization.
Environmental factors contributing to variation can include climate, nutrition, and conditions.

Identify similarities in goats of the same species.
- Common traits (e.g., species-specific features).
Identify differences in the same species.
- Variations in color, size, or features.

Human traits can be influenced by environment: e.g., exercise increases muscle mass, sunlight darkens skin.

The Theory of Natural Selection: Explains how species adapt and evolve based on hereditary genetic traits and environmental pressures.
Example: Long necks in giraffes; only those with advantageous traits (long necks) survived food scarcity, leading to offspring inheriting these traits over time.

Charles Darwin's observation of finches on the Galápagos Islands highlights the adaptive evolution based on beak shape.
Resistant Bacteria and Insect Resistance:
- Development of antibiotic resistance due to genetic variation and reproduction of resistant strains.
- Insecticide resistance develops similarly, leading to less effective pest control.

Define natural selection: The process wherein organisms with traits advantageous for survival reproduce more successfully.
Factors that affect survival: Environmental conditions, predator presence, resource availability.

Definition of Population: A group of organisms of the same species within a defined habitat at a specific time.
- Population increases with more births than deaths; decreases vice versa.
Extinction Factors: Environmental changes that exceed a species' adaptive capacity.
- Modern concerns include climate change and habitat loss leading to possible extinctions.

Asteroid strikes, invasive species, competition, and pollution are highlighted as potential extinction drivers.