Modern Genetics since Mendel Beyond Dominant and Recessive

Modern 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.