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.