modern genetics genetics since mendel. beyond dominant and recessive alleles some alleles are...
TRANSCRIPT
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.