Genetics

and

Heredity

The genetic material for an organism is contained in the nucleus of its cells. Inside the nucleus are chromosomes made of DNA (deoxyribonucleic acid). A segment of DNA is called a gene. Genes have the codes for the characteristics or traits of the organism.

Organisms reproduce in one of 2 ways.

Asexual reproduction is reproduction by one parent. The parent cell produces an identical copy of itself in this type of reproduction. When you cut your finger, it is healed by your skin cells going through asexual reproduction, making new identical skin cells.

Sexual reproduction is reproduction by two parents. Sex cells are produce by organisms that reproduce through sexual reproduction. A male sex cell is called sperm and a female sex cell is the egg. When a sperm cell and an egg cell join, fertilization has happened.

Heredity is the passing of traits from parents to their offspring. Offspring resemble their parents because they inherit genetic material from their parents. Organisms that are produced by sexual reproduction inherit or receive two genes for every trait, one from the mother and one from the father. Humans receive 23 pairs of chromosomes or 46 chromosomes. 23 chromosomes are from the mother and 23 from the father.

Traits are the characteristics of organisms. Each chromosome, in the nucleus of a cell, is made of DNA. Each chromosome is divided into units called genes. Genes have the information that controls certain traits. A dominant gene is a gene that prevents the expression of another gene. A dominant gene is represented by a capital letter. A recessive gene is a gene whose expression is hidden by a dominant gene. A lower case letter is used to represent a recessive gene.

A purebred or homozygous offspring (homo means same) has two of the same genes either two dominant or two recessive for a trait. A hybrid or heterozygous offspring (hetero means different) has two different genes one dominant and one recessive for a trait. Genotype is the gene combination. The combinations can either be homozygous or heterozygous.Phenotype is the physical appearance of the gene combination. The physical appearance can be either a dominant trait or a recessive trait.

In selective breeding, organisms that have certain desired traits are mated to produce offspring with the desired traits of both parents. The desired traits are produced by the combination of genetic material that the offspring inherit from both of their parents.

Uses of Selective Breeding•High yielding crops, such as wheat are produced by collecting the seeds from only the plants that have a good yield of wheat.

•Disease resistant crops can be developed. •Animals such as dogs and cats are bred for fashion. They may also be bred to do a particular job like sheepdogs.

•Animals on farms are bred so that they produce more food, for example, cows with better meat, hens that lay more eggs.http://www.crossleyheath.org.uk/biology/stem/3horses.htm

Charles Darwin was a naturalist- a scientist who studies organisms in their natural habitat. He developed the theory of Natural Selection which states that organisms that are the best adapted to their environment are the ones that survive and reproduce.

His theory further states:1. That more young are produced than can survive, 2. Organisms compete for needed resources, 3. Variations are passed from parents to offspring, and 4. Only those organisms that reproduce pass traits to the next generation.

How Darwin Came Up with the Theory of Natural SelectionAfter graduating from Cambridge college, Charles Darwin got a job on a British Navy mapping expedition going around the world on a five year long voyage. One of the places Darwin visited on this trip was the Galapagos in the Eastern Pacific Ocean off the coast of South America. Darwin observed one species of birds called finches on mainland South America. Darwin then observed 13 different species of finches on the Galapagos islands. He noticed that the birds differed from each other in beak shape. He also noticed that the beak shape matched the diet of the bird. Darwin concluded that the original species of finches came from South America, dispersed through the Galapagos Islands, and changed anatomically over time to adapt to their environment. The change allow the birds to survive and reproduce.

The Hierarchy The Hierarchy of Lifeof Life

The smallest unit of structure performing functions in organisms

is the

cell.

Many specialized cells working

together form

tissues.

Tissues working together form

organs.

Organs working together form

organ systems.

Organ systems working together form

organisms.

All of the same type of organisms living together in an area form a

population.

All of the different populations living together in an area form a

community.

All of the communities in an area (biotic factors) together with the

abiotic factors form an

Ecosystem.

Cell Tissue

Organ

Organ Syste

m

Organism

Population

Community

Ecosystem

The Hierarchy of Life

Cell Tissue

Organ

Organ Syste

m