Presentation on theme: "Genetics: A Monk a Pea and a Fly. Mendel and His Peas Born in Czech Republic in 1822 Studied math in Vienna Was in charge of the monastery garden Conducted."— Presentation transcript:
Dominant and Recessive Traits Noticed traits in the F 1 were not a blend of the parents but, instead favored one parent Trait that shows up the F 1 generation is Dominant the trait that is masked is Recessive Today : Traits chemical factors = Genes Forms of a trait = Alleles
The F 1 Cross Mendel then crossed the F 1 plants and the recessive trait reappeared! What happened? *Segregation : Alleles on homologous chromosomes separate when sex cells are produced Think about the logic here
Genotypes and Phenotypes Genotype : expression of alleles present Dominant alleles : Capital first letter of the dominant trait Recessive alleles : Lower case script of the first letter of the dominant trait Homozygote : Two of the same allele Heterozygote : Two different alleles Phenotype : Actual visible trait
Example : Flower color Purple (P) is dominant to white (p) Cross a pure breeding plant with purple flowers with a pure breeding plant with white flowers. 1) Determine genotypes 2) Segregate alleles 3) Perform cross
Probability and Genetics Chance of an event occurring : probability Does not indicate something will happen only the likelihood that it can happen Allele combinations follow rules of probability Probabilities in genetics can be determined using simple math or Punnett squares
Mr. Curry’s Never Miss, Easy, Solves Every Type of Genetics Problem Method 1.Define alleles 2.Define phenotypes associated with genotypes 3.Write out cross 4.Produce gametes 5.Perform cross (Punnett square) 6.Determine genotypic and phenotypic ratios of offspring 7.Answer the problem
Typical Monohybrid Homozygous Dominant X Homozygous Recessive P= F 1 = F 2 =
Two Traits at Once : Dihybrid Cross How do you determine inheritance for two traits at once? - Dihybrid Cross Just remember : Segregation and Independent Assortment (For now, these genes exist on separate chromosomes)
In the fruit fly Drosophila melanogaster, vestigial wings and hairy body are produced by two recessive alleles carried on different chromosomes. The normal alleles, long wings and hairless body, are dominant. If a vestigial-winged, hairy male is crossed with a female homozygous for both of the normal traits, what would be the phenotypes and genotypes of their progeny? If the F 1 generation was allowed to mate randomly among themselves, what phenotypes and genotypes would be expected among the F 2 ’s, and in what proportions?
In some breeds of dogs, a dominant allele controls the characteristic of barking while trailing. In these dogs, another, independent gene controls ear shape, erect ears being dominant over floppy ears. If a dog breeder wants to produce a true-breeding strain of floppy-eared dogs that bark on the trail, how should she proceed, knowing that the alleles for erect ears and silent trailing are present in her kennels?
P cross = Homozygous Dominant X Homozygous Recessive P= F 1 = F 2 =
Other Types of Inheritance Not all genes are dominant or recessive Sometimes get both alleles, a modified form or the dominant or something new altogether
Incomplete Dominance Two alleles produce three phenotypes Third phenotype is a muted version of the “dominant” Example 4 O’clock flowers RR = Red RW= Pink WW = White
Codominance When two alleles are both equally expressed in the heterozygote Example : ABO bloodtypes I A I A, I A i =A type blood I B I B, I B i = B type blood I A I B = AB type blood ii = O type blood
Sex Determination In all animals : Sex is determined by the combination of sex chromosomes (23 rd pair in humans) XX = female Xy = male
Polygenic Inheritance Traits are governed by more than one gene Most traits are polygenic Each gene may have two or more alleles Many genes can be codominant or incompletely dominant Heterozygotes are intermediate in phenotype
A recessive gene combination will effect the phenotype
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