Modern Genetics

Genetics since Mendel

Beyond Dominant and Recessive Alleles

• Some alleles are neither dominant or recessive, and many traits are controlled by multiple alleles or multiple genes.

• Incomplete dominance: one allele is not completely dominant over another. A red flower crossed with a white flower, produce pink flowers. (blending)

• Codominance: Both alleles contribute to the phenotype of the organism. Black chicken crossed to a white chicken produce a black and white chicken

Traits controlled by many genes

• The genes act together as a group to produce a single trait.

• At least 4 genes control height in humans

• Skin color is also controlled by many genes.

The Sex chromosomes

• The sex chromosomes are one of the 23 pairs of chromosomes in each body cell.

• The sex chromosomes carry genes that determine whether a person is male or female. They also carry genes that determine other traits.

• Girl = XX• Boy = XY

Sex-Linked Genes

• The genes for some human traits are carried on the sex chromosome.

• Genes on the X and Y chromosomes are often called sex-linked genes because their alleles are passed from parent to child on a sex chromosome.

• Traits controlled by sex-linked genes are called sex-linked traits.

• Example: red/green color blindness

The Effect of the Environment

• Many of a person’s characteristics are determined by an interaction between genes and the environment.

• For example, a person’s diet could affect a person’s height.

Causes of human genetic disorders

• A genetic disorder is an abnormal condition that a person inherits through genes or chromosomes.

• Some are caused by mutations in the DNA.

• Others are caused by changes in the overall structure or number of chromosomes.

Mutation

• A mutation is an error that occurs in the DNA when it is copied inside of a cell. Mutations are changes in genes.

• Not all mutation are harmful. They may have no effect and in rare cases it may be helpful.

Examples of Genetic Disorders

• Cystic fibrosis- Recessive genes• Color blindness• Hemophilia• Sickle cell • Celiac• Down syndrome

Pedigrees

• One of the important tools geneticists use to trace the inheritance of traits in humans is pedigree.

• A pedigree chart tracks which members of a family have a particular trait.

Pedigree ChartsCircle = FemaleSquare = Male

Karyotypes

• A karyotype is a picture of all the chromosomes in a cell.

• It can reveal if a person has the correct number of chromosomes

Normal Female

Normal Male

Downs Syndrome

Advances in Genetics

Selective Breeding

• The process of selecting organisms with desired traits to be parents of the next generation.

Inbreeding

• The technique of inbreeding involves crossing two individuals that have similar characteristics.

• Inbred organisms are genetically very similar, because of this inbreeding increases the probability that organisms may inherit alleles that lead to genetic disorders.

Hybridization

• In hybridization breeders cross two genetically different individuals.

• The hybrid is bred to have the best traits from both parents.

Cloning

• A clone is an organism that has exactly the same genes as the organism from which it was produced.

• www.brainpop.com • (cloning)

Genetic Engineering

• Genes from one organism are transferred into the DNA of another organism.

• Genetic engineering can produce medicines and improve crops.

• Genetically engineered bacteria produce human insulin for diabetics.

• Genetically engineered crops can resist pests or survive in cold temperatures or poor soil.

Gene Therapy

• Someday it may be possible to use genetic engineering to correct some genetic disorders in humans.

• This involves inserting copies of a gene directly into a person’s cells.

The Human Genome Project

• A genome is all the DNA in one cell of an organism.

• The main goal of the Human Genome Project was to identify the DNA sequence of every gene in the human genome. It was completed in May 2006.

• Scientists estimate that human DNA has around 25,000 genes.

DNA Fingerprinting

• DNA from a person’s cell is broken down into small fragments.

• Selected fragments are used to produce a pattern called a DNA fingerprint.

• Except for idenitcal twins no two people have exactly the same DNA fingerprint.