Chapter 14 Mendel genetics

Gregor Mendel Pea plants –Advantages Variety of characteristics –Seed color Many different traits –Yellow, green

To begin Self pollination –True breed –Asexual –P generation Cross pollination –Hybrid –F 1 generation

Next F 1 generation Self pollinate F 2 generation –the law of segregation – the law of independent assortment.

Law of segregation Dominant alleles –The one expressed Recessive alleles –The one masked –Alleles appear on certain locus on a certain chromosome

Law of segregation Where do the alleles come from? If the alleles differ, than one becomes dominant and the other recessive

Law of Segregation States: That the two alleles for a heritable character separate and segregate during gamete production and end up in different gametes (meiosis – homologous chromosomes)

Punnett Squares Mendel used the probability chart to guess the genetic outcome Dominant – big letter Recessive- small letter

Vocabulary Homozygous – identical alleles for a character Heterozygous – different alleles for a character Genotype – genetic make up Phenotype – physical traits Monohybrid – one allele type Dihybrid – two allele types

Law of independent assortment Dihybrids produced a 9:3:3:1 ratio States Each pair of alleles segregates independently during gamete formation *We are talking about genes on nonhomologous chromosomes

Multiplication Rule The outcome of one coin toss has no impact on the next coin toss –Independent …just like distribution of alleles

Multiplication Rule 1. compute the probability of each independent event 2. multiply the individual probabilities to get the probability of both occurring at the same time

practice What is the probability that you will get a TTRR- tall red plant in a dihybrid

Rule of addition The probability of an event can be made in two or more different ways 1. compute each independently 2. add the probabilities

We can combine the two What is the probability of an offspring having two recessive phenotypes for at least two or three traits resulting from a trihybrid between PpYyRr and Ppyyrr What are all the possible genotypes?

Use rule of multiplication first Start with ppyyRr pp= yy= Rr= All together =

Rule of multiplication Now do it for each genotype set: DO YOU TRUST ME ppYyrr= 1/16 Ppyyrr= 1/8 Ppyyrr= 1/16

Now addition The chance that a given offspring will have at least two recessive traits is 1/16 + 1/8 + 1/16 + 1/16 + 1/16 = 6/16

Deviations from Mendelian patterns Some alleles behave differently in relation to each other –Codominance Two alleles affect the phenotype –Incomplete dominance Two heterozygous alleles show an intermediate phenotype

Common misconceptions T or F because the allele is dominant it is more prevalent that the recessive allele T or F the nucleotide sequence of the dominant allele and recessive allele interact on the chromosome

Extra Information Pleitropic- most genes affect more than one phenotypic character –One gene can affect a number of characteristics –Example : sickle cell Swollen hands and feet, prone to infections, growth delays, vision problems

Extra Information Epistasis- a gene at one locus alters the phenotypic expression of a gene at a second locus –Example: albinism

Pedigrees