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 Charts Circle = Female Square = 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.