Bio 391 CHAPTER 13 MENDELIAN GENETICS. DNA vocabulary there are 4 chromatids in a tetrad.

Bio 391

CHAPTER 13

MENDELIANGENETICS

DNA vocabularythere are 4 chromatids in a

tetrad

MeiosisProcess of creating 4

DIFFERENT haploid gametes

Sexual Reproduction is an Evolutionary Advantage:

Mixing of Genes = More Possibilities

Beginnings Of A New Organism

Fertilization- union of the gametes

• Sperm – carry one set of chromosomes / genetic material from the father

• Egg – carry one set of chromosomes / genetic material from the mother

• When united, the two sets of chromosomes unite to create a genetically unique organism

ALLELES• Traits are passed through generations– Traits are controlled by

“Genes” • Mendel called them

“factors”

– Genes can have multiple forms:

• “Alleles” = different forms of the same gene– EX: eye color alleles– Blue, green, brown…– One person is only

capable of having 2 alleles

• Capital letters representing an allele = a DOMINANTDOMINANT allele

• lowercase letters representing an allele = a recessiverecessive allele

Gregor Mendel: The father of genetics

• Manually cross pollinated the pea plants in his garden

• He used “true-breeding” parents– This meant that those plants always produced

offspring that looked identical to the parents– Crossed a true-breeding plant with a specific

trait with a true-breeding plant with a different trait

• Called the offspring hybrids

• As a result of his work, developed three genetic principles– Dominance, Segregation, Independent

Assortment

Principle of Dominance

• When 2 True-breeding plants were crossed, only 1 trait showed in the next generation (F1)

• Some alleles are dominant & others are recessive

• Was that trait gone forever?

Law of Segregation

• When the F1 generations were self-pollinated, the recessive trait reappeared.

• For each trait an individual has two alleles (one from each parent). In turn, each individual can only pass one or the other of its alleles to its offspring.

Mendel + Meiosis

• Mendelian inheritance reflects the rules of probability

• Rule of Multiplication “and”– Chance that two or more independent events

occur simultaneously• Flip a coin twice – probability of getting two heads

• Rule of Addition “or”– Chance of an event that can occur in two or

more different ways• Flip a coin – probability of getting a heads or a tails

The Rules of Probability

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Probability & Punnett Squares

• Dominant & Recessive

• Homozygous & Heterozygous

• Genotype & Phenotype

Law of INDEPENDENT ASSORTMENT

• The inheritance of one gene does not influence the inheritance of another.

• In meiosis, the chromosomes line up randomly on the equator to be separated.

• If your parents are heterozygous for any traits, this leads to lots of possibilities!

Mendel discovered this through experimentation: rryy x RRYY

DIHYBRID CROSS

PatternsA Het x Het dihybrid cross yields the typical

genotypic ratio of:

9: 3: 3: 1