The Genetic Engine

How Does it Work?

PEER.tamu.edu 2010

What is “Genetics”??

• The study of how traits are inherited (passed on to the next generation) and how differences among individuals arise

• The study of the cellular compounds that carry genetic information

What are DNA?• The molecules that

carry the genetic instructions for making living organisms

What does DNA look like?

A DNA molecule looks like a twisted ladder! It has two strands of bases twisted around each other and linked together between the bases.

bases

DNA strand

How is DNA stored in the cell?

DNA is coiled tightly into an x-like structure called a chromosome. Chromosomes are in the nucleus of every cell.

Chromosomes viewed under a microscope.

What is a Gene?•A specific sequence of bases pairs that

contains the “code” for making a protein •Genes are called the “basic unit of heredity”

because they are passed from parents to offspring.

Reproduction

Reproduction

• Reproduction: the process by which organisms generate new individuals of the same kind

• Heredity: the passage of genetic instructions, through reproduction, from one generation to the next

Gregor Mendel (1822-1884)

“The Father of Modern Genetics”

Mendel made several hypotheses:

1. Each adult has two of every gene.

2. In reproduction, each parent contributes one of each gene to its offspring, so that the offspring has two full sets of genes too.

3. The combination of genes determines the traits of the offspring.

He was right!

Genes, Alleles, and Chromosomes

Each gene can have two or more versions; the different versions are called alleles.

Humans have 23 pairs of chromosomes for a total of 46.

Heterozygous: Individual has 2 different alleles for a gene

Homozygous: Individual has the 2 of the same alleles for a gene

Genotype & Phenotype

• Genotype: The specific combination of alleles of an organism

• Phenotype: The observable traits of an organism; are the result of the interaction between genotype and environment

+

genotype

environment

phenotype

Sexual Reproduction• Requires two individuals• Each individual contributes genetic information,

so the offspring will inherit half of their DNA from each parent. The offspring will all be different from either parent.

• Examples: plants & animals

Sexual Reproduction

Like its parents, the offspring will have 2 of every gene. One is from its father (blue) and one is from its mother (pink). The different

combinations of genes will produce unique offspring.

Asexual Reproduction• One organism produces offspring

• All offspring are identical (have the same genes) as each other and as the parent.– Examples: bacteria & plants

Natural Selection &

Adaptation

Mutation:A change in a DNA sequence

-They can be good!!! Mutations can change a trait in such a way that the survival of the organism is improved.

-Some mutations are inherited; some are not. Inherited mutations can affect the long-term survival of a whole population of organisms.

Fitness & Adaptation• Fitness: How well an organism is able to

survive in its environment and transmit its genes to the next generation

• Adaptation: A characteristic or trait that improves an organism’s fitness

4 Types of Adaptations:

• Reasons for adaptation– To suit their environment– To protect them from predators– To help them find food– To help them reproduce

How do adaptations happen??

Adaptation by Natural Selection: the process where heritable traits that make an organism more “fit” for its environment become more common over many generations

1. A heritable mutation in a gene changes a trait and increases an individual’s fitness.

2. The offspring of that individual are more fit and reproduce more themselves.

3. After many generations, most (or all) of the individuals have the new trait.

The Process of Adaptation by Natural Selection:

Finches and Natural Selection:Organism:

Galapagos finches

Adaptation:

beak sizes and shapes are specialized to the different food sources on the islands

Selection:

Competition for food selected for different beak shapes

More Natural Selection at Work!

LH RH

A species of scale-eating fish called cichlids that live in Africa's Lake Tanganyika

Adaptation:

Organism:

There are two types of scale-eating cichlids—those with mouths turned to the left and those to the right—that prey on the scales of other fish in the lake

Selection:

If there are more “left-handed” cichlids, fish in the lake learn to watch their right side and the “right-handed” cichlids get more food and their population increases. Eventually, the prey fish learn to watch their left side and the advantage switches.

Artificial selectionSelective breeding: the selection of certain seeds or animals for reproduction in order to influence the traits inherited by the next generation

How Artificial Selection Affects our Dinner Table

Giving Thanks - Science Supersized Your Turkey

Dinner!!

Genetic Engineering…

is the lab technique of removing, modifying, or adding genes to an organism

– Often the goal is to introduce a useful trait• Example: yellow/golden rice with vitamin A for eye

health

Vocabulary Words• Genetics• Heredity• DNA• Gene• Chromosome• Allele• Genotype• Phenotype• Heterozygous• Homozygous• Mutation• Fitness• Adaptation

• Asexual reproduction• Sexual reproduction• Natural selection• Selective breeding• Genetic engineering