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Law of Independent Assortment Genetics…continued… Law of Segregation Law of Independent Assortment Dihybrid Crosses Karyotyping DNA Fingerprinting

The Law of Segregation and the Law of Independent Assortment

Law of Dominance In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. All the offspring will be heterozygous and express only the dominant trait. RR x rr yields all Rr (round seeds)

Law of Dominance

Independent Assortment Segregation Process that separates the two alleles (ex: Tt) of a gene during gamete formation (meiosis) Independent Assortment genes are inherited independently of each other

Law of Segregation During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.

Applying the Law of Segregation

Law of Independent Assortment Alleles for different traits are distributed to sex cells (& offspring) independently of one another. This law can be illustrated using dihybrid crosses.

Dihybrid Cross A breeding experiment that tracks the inheritance of two traits. Mendel’s “Law of Independent Assortment” a. Each pair of alleles segregates independently during gamete formation b. Formula: 2n (n = # of heterozygotes)

Dihybrid Cross RrGg x RrGg Traits: Seed shape & Seed color F O I L Traits: Seed shape & Seed color Alleles: R round r wrinkled G green g yellow RrGg x RrGg RG Rg rG rg RG Rg rG rg All possible gamete combinations

Dihybrid Cross RG Rg rG rg RG Rg rG rg

Dihybrid Cross RG Rg rG rg Round/Green: 9 Round/yellow: 3 wrinkled/Green: 3 wrinkled/yellow: 1 RRGG RRGg RrGG RrGg RRgg Rrgg rrGG rrGg rrgg 9:3:3:1 phenotypic ratio

Let’s do it another way… Rule of Multiplication: Independent events in sequence (law of Independent Assortment) “and”…(x) What are the odds of flipping a coin 3 times and getting tails all 3 times? They are ALL independent of one another…just as traits.

What are the odds that an offspring will be Heterozygous for two traits if the parents are both heterozygous for the same two traits? Parents: AaBb x AaBb

What are the odds that an offspring will be Heterozygous for both traits if the parents genotypes are: AABb x AaBB

What are the odds that an offspring will be Heterozygous for 3 traits if the parents genotypes are: AabbCC x AABbcc

Test Cross A mating between an individual of unknown genotype and a homozygous recessive individual. Example: bbC__ x bbcc BB = brown eyes Bb = brown eyes bb = blue eyes CC = curly hair Cc = curly hair cc = straight hair bC b___ bc

Test Cross Possible results: bC b___ bc bbCc C bC b___ bc bbCc bbcc or

Summary of Mendel’s laws PARENT CROSS OFFSPRING DOMINANCE TT x tt tall x short 100% Tt tall SEGREGATION Tt x Tt tall x tall 75% tall 25% short INDEPENDENT ASSORTMENT RrGg x RrGg round & green x round & green 9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow pods

Genetic fingerprinting 13 Genetic fingerprinting DNA analysis can be used for catching criminals, establishing parentage, finding how closely organisms are related and many other applications. The pattern of bands in a gel electrophoresis is known as a genetic fingerprint or a ‘genetic profile’ The genetic fingerprint found in a sample of blood or other tissue (containing DNA) is then compared to other known samples to determine it’s origin…based on how similar the banding patterns are to each other. A DNA sample can be obtained from the suspect using blood, cheek epithelial cells taken from the mouth lining or even the cells clinging to the root of a hair…as long as the tissue contains DNA Genetic fingerprinting

S Sample from crime scene DNA profiles 16 V S S1 S2 S3 V Victim S Sample from crime scene S1 Suspect 1 S2 Suspect 2 S3 Suspect 3 More than 20 fragments from Suspect 1 match those taken from the crime scene

Paternity test 19 mother father position of restriction fragment part of DNA strand child The vertical lines should not be confused with chromosomes. They each represent lengths of double-stranded DNA in a single chromosome Child will receive one copy of the restriction fragment from the mother and one from the father. It could be any one of these combinations

There is a match between one of the child’s restriction fragments 20 Genetic fingerprint of … 1 mother 2 child 3 possible father A 4 possible father B There is a match between one of the child’s restriction fragments and one of the mother’s. There is also a match between the child’s other fragment and one from possible father A. Neither of the child’s restriction fragments match those of possible father B 1 2 3 4 Starting position of sample Paternity test

Picture of chromosomes arranged in pairs Karyotype Picture of chromosomes arranged in pairs sex chromosomes – pair #23 that determine the sex of an individual (XX or XY) autosomes (autosomal chromosomes) – the remaining 22 pairs of chromosomes