Review What does homozygous dominant mean? Example: What does heterozygous mean? What is another word for heterozygous? Where do male genes go on a punnet square? Where do female genes go on a punnet square?

Chapter 11 Introduction to Genetics 11-3 Exploring Mendelian Genetics

Does that happen independently of other genes? Mendel had another question… When a pair of alleles (genes segregate (separate) in the formation of sex cells: What did he do? Does that happen independently of other genes? He crossed 2 plants where he could follow 2 different traits as they passed from one generation to the next. For example: Seed shape-seed color ROUND YELLOW x wrinkled green RR YY x rr yy

The 1st generation was hybrid for each trait Now that he had a hybrid plant, he crossed 2 of them RrYy Round/Yellow RrYy x RrYy Round/Yellow x Round/Yellow

How do 2 hybrid genes separate during the formation of sex cells? RrYy RY, Ry rY, ry

RY Ry rY ry RY Ry rY ry RrYy RRYY RRYy RrYY RRYy RRyy RrYy Rryy rrYy Round/Yellow Round/Yellow Round/Yellow Round/Yellow RRYy RRyy RrYy Rryy Round/Yellow Round/green Round/Yellow Round/green rrYy RrYY RrYy rrYY Round/Yellow Round/Yellow wrinkled/Yellow wrinkled/Yellow RrYy Rryy rrYy rryy Round/Yellow Round/green wrinkled/Yellow wrinkled/green

Because 4 phenotypes were produced, it proves that the alleles RY Ry rY ry 1 RY Ry rY ry RrYy RRYY RRYy RrYY Round/Yellow Round/Yellow Round/Yellow Round/Yellow 2 RRYy RRyy RrYy Rryy Round/Yellow Round/green Round/Yellow Round/green 3 rrYy RrYY RrYy rrYY Round/Yellow Round/Yellow wrinkled/Yellow wrinkled/Yellow 4 RrYy Rryy rrYy rryy Round/Yellow Round/green wrinkled/Yellow wrinkled/green Because 4 phenotypes were produced, it proves that the alleles separated independently of each other when sex cells were formed.

Count how many of each there are List the 4 phenotypes Count how many of each there are Round Yellow Round green wrinkled Yellow wrinkled green 9 RY 3 Ry 3 rY 1 ry Ratio of a DIHYBRID Cross: 9:3:3:1

THE LAW OF INDEPENDENT ASSORTMENT Why is this important? Genes for different traits separate (segregate) independently from each other in the formation of sex cells explains why we are so different

Summary of Mendel’s Principles The inheritance of traits is determined by genes passed from parent to offspring Some genes are dominant, others are recessive Each trait is governed by 2 genes or alleles, one from each parent. These genes are segregated (separated from each other) when sex cells (gametes) are formed These genes, or alleles, segregate independently from each other

Exceptions to the Law of Independent Assortment Why are there exceptions to the Law of Independent Assortment What are the exceptions? Not all traits are governed by 2 genes Some genes are not dominant or recessive Incomplete Dominance Codominance Multiple Alleles

Incomplete Dominance Rr Rr r r r Rr Rr

Incomplete Dominance Which gene is dominant? In 4 o’clock flowers: RR = red Rr =pink (not RED as expected) rr = white The hybrid phenotype is a blend of both dominant and recessive Neither.

Incomplete Dominance

Both genes (alleles) contribute to the appearance (phenotype) Codominance Both genes (alleles) contribute to the appearance (phenotype) In certain chickens The gene for Black feathers is codominant with the gene for white feathers Hybrids are speckled black and white and called “erminette”

So more than 2 genes contribute to the phenotype Rabbits can be Multiple alleles More than 2 alleles can exist in a population, not in a single organism So more than 2 genes contribute to the phenotype Rabbits can be CC - Full color cch cch - Chinchilla - partial defect in pigmentation ch ch - Himalayan - color in certain parts of the body cc -albino - no color, recessive D O M I N A T

Full color (CC)

Chinchilla (cchcch) Partial defect in pigmintation

Himalayan (chch) - color in certain parts of the body

Albino (cc) - no color recessive to others

Can chinchillas hide all? Why do the following genotypes all appear ‘full color’? Ccch - full color Cch - full color Cc - full color The gene for full color dominates all the others Can chinchillas hide all? Full Color Chinchilla Himalayan albino

Do Mendel’s genetic principles apply to animals as well? Are genes the ONLY factor that determine an organisms characteristics? Yes. No The environment also plays a role Example: Identical twins brought up in different environments can be very different Plants with genes for good height and color also depend on soil and water for optimal growth

Homework p. 274 # 1, 2, 4 Genetics crossword Genetics test practice – 50 questions All to be completed by Thursday – end of class can collaborate with teams on this day TEST – Monday March 2nd

There are 3 alleles for the human blood type: IA Type A IB Type B ii Type O (recessive blood type) Type A genes: IAIA, IAi Type B genes: IBIB, IBi Type AB genes: IAIB (co-dominant) Type o genes: ii

Create your own dihybrid cross Create the gene chart TT - tall Tt - tall tt - short Write the hybrid genotype for each parent. Independently assort to create gametes for each parent Set up the punnett square What are the answers-offspring?