2Genetics Since Mendel What have we found out since Mendel? Since Mendel’s experiments, scientists have found that genetic inheritance can be much more complicated than the simple, dominant-recessive inheritance that Mendel saw in pea plants.
3Incomplete Dominance Incomplete Dominance Occurs when offspring of two homozygous parents show an intermediate phenotype.The heterozygous form is in between the dominant and recessive homozygous forms.
4Incomplete Dominance Incomplete Dominance Example: Snapdragons: Crossing a purebred white snapdragon with a purebred red snapdragon produces a pink snapdragon.
5Multiple Alleles Multiple Alleles Trait is controlled by more than two alleles.Produce more than 3 phenotypes for the trait.
6Multiple Alleles Example: Multiple Alleles Blood Type: Alleles: IA IB and iPhenotypes: A, B, AB, OType O is recessive to types A and B.Types A and B are both expressed in the phenotype when paired together.
7Polygenic Inheritance Occurs when a group of gene pairs act together to produce a trait.Traits are controlled by alleles from more than one gene.A wide variety of phenotypes are produced.Examples:Hair, eye, and skin color
8Impact of the Environment Environmental influence on genetics:Environmental influences can be internal or external.Examples:A boy who has genetics to be six feet tall is malnourished as a child and is only five foot eight inches tall.Male birds exhibit brighter feathers than female birds.
9Human Genes and Mutations What is a mutation again?Error in the DNA sequence.Can be harmful, helpful, or null.Can be caused by mistakes in replication or by external agents called mutagens.
10Human Genes and Mutations Chromosome DisordersAn organism receives too many or too few chromosomes as a result of mistakes in meiosis.Usually fatalExample:Down’s syndrome3 copies of chromosome 21.
11Recessive Genetic Disorders Disorder only appears if an individual has both recessive alleles.Parents are carriers (heterozygous) and do not show symptoms of the disorder.
12Recessive Genetic Disorders Example:Cystic fibrosisProduction of thick instead of thin mucous in the lungs and intestinal tract.Most common genetic disorder leading to death in Caucasian Americans.
13Determination of Gender Boy or Girl?Sperm cells have either an X or a Y chromosome.Egg cells have only an X chromosome.Males – XYFemales - XX
14Sex-Linked Disorders Sex-linked Disorders Alleles controlling the genetic disorder are linked to either the X or the Y chromosome.
15Sex-Linked Disorders Sex-linked Disorders Example: Color blindness Recessive allele linked to the X-chromosome.All males with the recessive allele are colorblind.Females must have two recessive alleles to be colorblind.
16Pedigrees Pedigrees Family tree for a certain trait. Used to determine inheritance patterns and probabilities and in breeding plants and animals.
17Pedigrees How to read a pedigree: Males – squares Females – circles Have the trait – coloredDoes not have the trait – emptyIs a carrier (heterozygous) – half-colored