6 ParentFirst filialCrossed 2 F1 plants to get F2Second Filial
7 Mendel’s Principle of Dominance One form of a hereditary trait – the dominant trait – prevents the expression of the other – the recessive traitEg. In peas, purple x white gives all purple offspringPurple is dominantWhite is recessive
9 Punnett SquaresShow all possible resulting offspring from a cross between 2 parents AND the probability of each offspringEach parent contributes 2 genes for a trait (alleles)Represent with lettersCapital = dominantLower case = recessiveHomozygous – alleles same eg. AA or aaHeterozygous – alleles different eg. Aa
11 Genotype vs. PhenotypeGenotype = actual genetic make-up an individual has – represented by lettersPhenotype = outward expression of the genotype – the protein that is produced.Eg. Let P = purple, and p = whiteGenotypes PP and Pp both have the same phenotype purplePP = homozygous dominantPp = heterozygouspp = homozygous recessive
12 Genotypic ratio = probable ratio of genotypes in offspring of a cross Eg. 1PP : 2Pp : 1 ppPhenotypic ratio = probable ratio of phenotypes resulting from the genotypic ratioEg. 3 purple : 1 white
13 Observed ratio = what actually occurs Expected ratio = the ratio expected based on probability (Punnett Square)Observed ratio = what actually occursWhy would these be different?
16 Mendel’s Principle of Segregation During gamete formation, the pair of genes responsible for each trait separates so that each gamete receives only one gene for each trait.This happens during meiosis I when homologous chromosomes separate (anaphase I)
19 Genes on different chromosomes sort independently into gametes Genes on different chromosomes sort independently into gametes. What if they are on the same chromosome?
20 Mendel’s Principle of Independent Assortment Genes for different traits segregate independently during gamete formation when they are located on different chromosomes..If they are on the same pair of homologous chromosomes, they are said to be “linked” and DO NOT sort independently.
21 Do “linked” genes sort independently into gametes? NO!meiosisAaBbCcDdEe
23 Test Cross Used to determine the unknown genotype of a dominant phenotype.Cross the dominant phenotype with a recessive phenotypeIf any of the offspring show recessive trait, the unknown parent was a heterozygote.
25 Incomplete DominanceHeterozygote’s phenotoype is intermediate between dominant and recessive – looks like a blending of the 2.Eg. Pink Four o’clock flowersGenotypic and phenotypic ratios same1 RR : 2 RW : 1 WW1 red : 2 pink : 1 white
26 CodominanceCodominance is when a heterozygote displays the protein products of both alleles.Roan cow has a mixture of both red and white hairs.
27 Multiple Alleles (I A = IB ) > i More than 2 different forms of an allele exist.Individual still has just 2.Blood Group alleles:(I A = IB ) > iBlood groups exhibit both codominance and multiple alleles
33 Sex-Linked TraitsThis is a pedigree chart showing the inheritance of hemophilia.Does hemophilia affect one gender more often?Why?
34 Sex-Linked Traits Try this test for red/green colorblindness… What do you see?
35 X-linked traitsX and Y are not entirely homologous, X is bigger and carries more genes.Males will have only one allele for traits carried only on the X called X-linked or sex-linked.Some examples of sex-linked traits are hemophilia, colorblindness, and eye color in Drosophila.X-linked disorders will present more in males.Regular chromosomes = autosomes (22 pairs)Pair 23 are sex chromosomes
36 Polygenic Inheritance – many genes affect a single trait – shows continuum. Eg hair color, height, skin color.