Genetics Gregor Mendel Chapter 11
Dec 22, 2015
Mendel
• Austrian Monk
• Was a local high school science teacher
• Job was to grow food for the entire monastery
• Became interested in how traits are passed from parents to offspring.
Mendel
• Crossed and controlled breeding of pea plants
• Used burlap sacks to control pollination of flowering pea plants
• Very controlled experiment
• Many generations in a short period of time
Mendel’s Work
• Crossed a tall pea plant with a tall pea plant, produced all tall plants.
• Crossed a short pea plant with a short pea plant, produced all short plants.
• Crossed a tall pea plant with a short plant, produced all tall plants.
• Took seeds from the previous cross, produced 3 tall plants and one short plant
Mendel’s Hypothesis
• Traits are controlled by factors (genes) which always occur in pairs
• Factors (genes) separate during the formation of sex cells (gametes).
• In a pair of factors (genes) one may mask or hide the effect of the other trait.
Genetic Terms
• Homozygous- two alleles that are the same, TT or tt
• Heterozygous- two alleles that are opposite, Tt (hybrid)
• genotype- using letters to represent traits, TT, Tt, tt.
• Phenotype-a physical description of a trait,
• Homozygous tall, heterozygous tall.
Genetics
• In pigs white coat color is dominant to black coat color. Curly tails are dominant to straight tails.
• Cross a heterozygous white coat, heterozygous curly tail male with a heterozygous white coat, heterozygous curly tail female. Predict the possible results.
Mendel’s research on Pea Plants
• E:\Gregor_Mendel_s_Reseach_on_Pea_Plants_and_His_Development_of_Theories_of_Inheritance.asf
Genetics
• In four ‘o’ clocks, red is incompletely dominant to white flower color. The heterozygous condition results in pink flowers.
• Cross a red flower with a pink flower and predict the results.
• Cross a pink flower with a pink flower and predict the results.
Incomplete dominance vs. Co- dominance
• Incomplete- you get a mixture. Red and white, you get pink.
• Co-dominance- both traits appear. Red and white to make roan.
• A and B blood types combine to make AB.
Sex Linked Traits
• Traits carried on X or Y chromosome.
• Most are carried on X chromosome.
• Therefore a male is 70 times more likely to have a sex-linked trait than a female.
Sex limited traits
• Traits carried by both sexes and controlled by the presence of sex hormones.
• Secondary sexual characteristics.
• Females- estrogen and progesterone
• Female traits- higher % of body fat vs. lower % of muscle tissue. Breast growth and production of eggs.
Sex Limited Traits cont.
• Males
• Voice change, growth of beard, production of sperm, Higher % of muscle tissue vs. lower % of body fat.
Sex Influenced Traits
• Traits that are dominant in one sex and recessive in the other trait.
• Male pattern baldness.
Polygenic Inheritance
• More than one pair of alleles codes for a trait.
• Skin color
• Hair color
• Eye color
• The more dominant traits, the darker, more recessive, lighter the color.
Selective Breeding
• Luther Burbank worked with potato plants to produce a potato that was resistant to disease.
• You take the best two individuals with qualities that are favorable, and allow them to mate.
• Hopefully the traits are passed to offspring.
Hybridization
• Crossing of two different organisms and trying to pass the traits to the offspring.
• Cross between a cow and a buffalo and producing a beefalo.
• Done with some domestic animals hoping to produce a new breed.
• Many hybrids are sterile.
Hybrids
• Crossing of two closely related but different individuals
• The goal is to get the best qualities of each individual
• Example beefalo
• Goal was to get an individual that had good tasting meat but was able to survive extreme harsh weather conditions.
Genetic Disorders
• Human disorders can be caused by dominant, or recessive genes. Some may exhibit co-dominance.
• Many of these disorders are from particular areas of the world. They have become more prevalent due to the breaking down of geographic and social barriers.
Genetic Disorders
• Most genetic disorders are autosomal, which means they occur on an autosome or any chromosome other than sex chromosome.
• Sex linked- occur on X or Y chromosome
• Color blindness, hemophilia
Nondisjunction
• Failure of a pair of chromosomes to separate during meiosis
• Trisomy- three chromosomes instead of the normal pair.
• Monosomy- one chromosome instead of the normal pair.
• May occur in any pair of chromosomes
Trisomy 21
• Downs Syndrome- results from nondisjunction in the 21st pair of chromosomes, they have 3 chromosomes instead of the normal pair.
Karotypes
• Used by Geneticist to determine genetic disorders.
• Take a photograph of chromosomes and then line them up to see if correct number exists or if part of a chromosome is missing.
Mutation
• Any change in the genetic code.
• Most mutations are harmless
• Most mutations correct themselves during the next cell division.
• Mutations may cause an abnormal growth of some types of cells, this may lead to various types of cancer.
Mutations cont.
• Mutations can be on the DNA level, allele level, or the chromosome level.
• Mutations may be harmful or lead to a genetic change.
• Some genetic change may be positive.
Genetic Engineering
• Manipulating DNA
• Gene Splicing, cut DNA at a specific point so that a new sequence of DNA can be introduced. Ex. Injecting the gene to produce insulin into bacteria so that it will produce insulin.