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–F1 generation

Next

• F1 generation• Self pollinate• F2 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• 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