genetics ature=endscreen&nr=1&v=yxkf dqo10re
TRANSCRIPT
Genetics
http://www.youtube.com/watch?feature=endscreen&NR=1&v=YxKFdQo10rE
Gregor Johann Mendel
• Austrian monk• How do mothers and fathers
pass down traits to their children?
• Mendel tested his idea of heredity on pea plants
• http://www.youtube.com/watch?v=EvR_Sdm1orU
• Pea plants is normally self-pollinating
• Easy to control the parental crosses
• Easily grown and matured quickly, producing many seeds
• Allowed him to study many generations over a relatively short period of time
• Showed several pairs of obvious, contrasting traits
Observed traits were called phenotypes
• After several years of self-pollinating the pea plants, Mendel established purebred plants• When self-pollinated, these plants always create
plants that look like themselves
• Mendel also cross bred the purebred plants that were different for only one contrasting pair of traits– The purebred parent plants were called the
P generation– The offspring were called hybrids– First generation of hybrids – F1 generation– Second generation of hybrids – F2
generation
Results?• The F1 generation
hybrids had the same trait
• The traits of tallness dominated the traits of dwarf-ness
• Mendel called them the dominant traits
• Trait that was not expressed = recessive trait
• Mendel crossed his F1 generation plants to determine whether they were identical to the P generation plants
• If they were, then F1 cross would produce only tall plants
• F2 generation yielded 3 tall plants and 1 dwarf plant
• Phenotypic ratio of F2 was 3:1– Proportion of individuals
in a generation that express a certain trait
• The F1 hybrid were different from the purebred tall plants
• The gene for plant height has two different forms (alleles): tall and dwarf– Tall = dominant– Dwarf = recessive
• He suggested that each plant’s phenotype was determined by a PAIR of alleles that could be identical or different
• The only way a plant to develop as a dwarf is if both its alleles are recessive
Mendel’s Law of Segregation
• Members of a pair of alleles for a given trait are segregated (separated) when gametes are formed
• Once Mendel came up with the Law of Segregation, he was able to describe the gene makeup, or genotype
• He used letters of the alphabet to represent the genes
• The allele for dominant trait was represented by T
• The allele for recessive trait was represented by t
• Purebred tall plant = TT
• Purebred dwarf plant = tt
• Hybrid tall plant = Tt
Homozygous
Heterozygous
Monohybrid CrossDrag-and-Drop Genetics: Monohybrid
MONOHYBRID PROBLEMS
• Problems dealing with one trait only ie. height or colour
1.Write the cross
2.Produce the gametes
3.Draw the Punnett square
4.List the phenotype and genotype ratios
• 1. In dinosaurs, the gene for sharp teeth (S) is dominant over the gene for dull teeth (s). Cross a heterozygous sharp toothed dinosaur with a dull-toothed dinosaur to produce the F1 (first generation) offspring.
• 2. Cross a homozygous sharp toothed dinosaur with a homozygous dull-toothed dinosaur to produce the F1 offspring.
• 3. Now cross two of the F1 generation offspring from question #2 to produce the F2 offspring.