The Genetic Engine

How Genetics Workscreated by Candace Seeve

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 is DNA?

• DNA—The chemical inside the nucleus of a cell that carries the genetic instructions for making living organisms.

What does DNA look like?

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

bases

DNA strand

How is DNA stored in the cell?

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

Chromosomes viewed under a microscope.

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

contains the “code” for making an organism. •Genes are called the “basic unit of heredity”

because they are passed on 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 from one generation to the next generation by reproduction.

Gregor Mendel (1822-1884)

“The Father of Modern Genetics”

Mendel’s hypothesis

1. Each adult has two of every gene.

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

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

HE WAS RIGHT!!!

Genes, Alleles, and Chromosomes

There is more than one version of a gene & the different versions are called alleles.

Humans have 23 pairs of chromosomes.

Heterozygous—Individual has 2 different alleles for a gene.

Homozygous—Individual has the 2 same alleles for a gene.

Genotype & Phenotype

• Genotype—The specific combination of alleles of an individual.

• Phenotype—The observable traits of an organism that are a result of its genotype and its environment.

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genotype

environment

phenotype

Sexual Reproduction• Requires two individuals. Each individual

contributes genetic information, so that the offspring will inherit ½ 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 that is identical to itself. The offspring will have the same genes as its parent.– Examples: bacteria & plants

Natural Selection &

Adaptation

MutationA change in a DNA sequence.

-Can be good!!! Mutations can change a trait that improves the survival of an organism.

-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 are more fit and reproduce more themselves.

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

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 island.

Selection:

Competition for food selected for different shaped beaks that could use the different food sources.

Natural Selection at Work!

LH RH

A species of scale-eating fish called cichlids living in Africa's Lake Tanganyika.

Adaptation:

Organism:

There are two types of scale-eating cichlids—cichlids with their mouth’s turned to the left or to the right—that prey on the scales of other fish in the lake.

Selection:

If there are more “left-handed” cichlids the other fish learn to watch their right side and the “right-handed” cichlids easily eat scales and their population increases until the prey fish learn to watch their left side and the advantage changes.

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

• The lab technique of removing, modifying or adding genes to an organism in order to introduce a useful trait.

– Yellow/golden rice with vitamin A for eye health in poor countries.

My Research: Identify genes responsible for drought resistance

and disease resistance in loblolly pine trees.

Why study loblolly pine?Why study disease & drought resistance?

How are we using Genetics?1. We examined the sequence of bases in thousands of genes in more

than 300 loblolly pine trees to identify the common alleles of those genes.

2. We examined the phenotypes of those individuals. We did experiments to test if some of the trees could resistant disease or grow better in droughts.

3. We used computer programs to find relationships between the drought & disease resistant phenotypes and the alleles that they had. We can use this information in the future for selective breeding programs.

Genetics Vocabulary Words• Genetics• DNA• Gene• Chromosome• Sexual Reproduction• Asexual Reproduction

Vocabulary

• Heredity

• Genotype

• Phenotype

• Asexual reproduction

• Sexual reproduction

• Allele

•Heterozygous•Homozygous

Vocabulary

• Mutation

• Fitness

• Adaptation

• Natural selection

• Selective breeding

• Genetic engineering