Words to know Test cross Genotype F1 generation Phenotype P generation Monohybrid cross Dihybrid cross Karyotype Punnett Square Mendel’s Principles Incomplete Dominance Codominance Multiple Alleles Genotype Phenotype Dominant Recessive Homozygous Heterozygous Gene Allele Gene symbol Genome

Mendel’s 4 Principle’s Inheritance of biological characteristics is determined by genes Principle of Dominance Law of Segregation Principle of Independent Assortment

Mendel’s 4 Principals Inheritance of biological characteristics is determined by genes Principal of Independent Assortment Genes for different traits can segregate independently during the formation of gametes. This principle helps account for many genetic variations in plants, animals and other organisms. Principle of Dominance When there are two or more alleles for a gene, some are dominant while others are recessive Law of Segregation In sexually reproducing organisms, adult cells have two copies of each gene—one from each parent; these genes segregate when GAMETES are formed

Exception to Mendel’s Principles Incomplete Dominance (blending) Red flower + white flower= pink flower Co-Dominance Chicken with black and white feathers Multiple Alleles Many different possible alleles for 1 gene (blood type) Polygenic traits Traits controlled by many traits (eye color height)

From Peas and fruit flies to humans… The Human Genome From Peas and fruit flies to humans…

What is a genome??? All the genetic information (genes) that make up an organism

What makes us human? Analyze human chromosome… Karotype Picture of all the chromosomes in an organism Autosomes CHROMOSOMES 1-44 (pairs 1-22) Autosomal chromsomes Sex chromosomes Determine a person’s sex (male XY or female XX) Chromosome 45 and 46 (set 23)

2 events that lead to genetic variation Crossing over During prophase 1 of meiosis 1 Segments of homologous chromosomes exchanged Independent Assortment In metaphase 1 of meiosis 1 When homologous chromosomes line up in random order along center of the cell in a random fashion

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Gregor Mendel 1822 Austrian monk University of Vienna In charge of the Garden

True breeding/Purebred Parts of the plant Female part-pistil (egg) Male part-stamen-pollen (sperm) Fertilization Produces new cell which develops into an embryo and is enclosed by a seed Self-pollinating Contain male and female parts Sperm cell in pollen fertilizes egg cells in flower Offspring inherit all traits of parent True breeding/Purebred Genetically identical organisms produced through self-pollination Allowed to self pollinate Tall plant Green seeds Cross Pollination Cut off male parts of one plant so it only had eggs Dusted it with pollen from a different plant

Cross Pollination Produces seeds that had two different parents Mendel could now cross bred plants with different parents

Terms Gene: chemical factors (sections of DNA) that determine specific traits Trait: a specific characteristic that varies from one individual to another. Allelle: different forms of a gene, that combined, determine a trait

Genotype: genetic make-up of an organism (the two alleles an organism has inherited from each parent for a trait) The two alleles carried on an organisms DNA Phenotype: physical characteristics or the OBSERVABLE version of the trait; the genotype will determine what phenotype organism has

Progeny Offspring P1 refers to parent generation F1 refers to first batch of offspring from original parents F2 refers to the offspring of the F1 organisms Dominant Allele for trait that will be expressed no matter what the other allele is (A) Recessive Allele for a trait that can only be expressed if dominant allele is ABSENT (a) Heterozygous phenotype will be Dominant (or codominant or incomplete dominance) Organism that has two different alleles for a trait Aa Homozygous (Dominant or Recessive) Organism that has two IDENTICAL alleles for a trait aa or AA

Punnett Square Diagram that shows possible genotypes and phenotypes Probability

Test Cross used to determine whether a plant or animal is homozygous or heterozygous for a particular trait Organism #1 with a DOMINANT phenotype and an UNKNOWN genotype (A ? ) is crossed with organism #2 who is homozygous recessive (aa) If #1 is homozygous Dominant (AA) for the trait, all offspring will be dominant for that trait If #1 is heterozygous dominant (Aa), then some of the offspring will show the recessive phenotype for that trait

Punnet Square Hybrids Offspring of crossing two parents with different versions of a trait Ex. Tall with Short; Purple with White Parents are the “P generation” Offspring are the “F1 generation/progeny” When two of the F1 plants are crossed, the offspring are referred to as the “F2 generation/progeny”

Ratios What is a ratio? Phenotypic ratios Genotypic ratios A comparison between multiple objects Phenotypic ratios Compares the number of different phenotypes for a cross # of Dominant Phenotype : # of Recessive Phenotype Genotypic ratios Compares the number of different genotypes for a cross 3 possibilities # of DD : # of Dd : # of dd Homozygous dominant DD Heterozygous dominant Dd Homozygous recessive dd

What are the phenotypes of the F1 generation? Probability of having a green pod? Probability of having a yellow pod? What are the genotypes for the F1 generation? What are the phenotypes of the F2 generation? What are the genotypes for the F2 generation?

Probability Def: The likelihood of an event happening It’s a way to predict the average outcome of a large number of events CANNOT predict the precise outcome of an event only the LIKELIHOOD of the event Flip a coin What is the probability of getting heads? What is the probability of getting tails? If you flip a coin 3 times…

If you flip a coin two times, does the first flip effect what you are going to get in the second flip? No… One event does not effect another event’s probability If there is a ¼ chance of having a white plant…the chances of having another white plant when crossing the plants again is still ¼ What are the chances of having 2 white plants after two fertilizations? ¼ x ¼ = 1/16

Things to keep in mind… Probability predicts the AVERAGE outcome of a LARGE number of events Cannot predict a precise outcome The larger the number of events the closer you will be to getting the expected results

Let’s look at Pea shape and pea color Round (R) vs. wrinkled (r) Yellow (Y) vs. green (y) Remember, there are 4 possible gametes If a parent is homozygous dominant (true-breeding dominant) for both shape and color, what will all possible gametes be? If a parent is homozygous recessive (true-breeding recessive) for both shape and color, what will all possible gametes be?

True breeding Round Yellow Peas Genotype (RRYY) Make a test cross of: True breeding Round Yellow Peas Genotype (RRYY) True breeding Wrinkled Green peas Genotype (rryy) ry ry ry ry RY RY RY RY

What is the phenotype of the F1 offspring? What is the genotype of the F1 offspring?

What this first cross told us… All F1 offspring were heterozygous for seed shape (round) and seed color (yellow) RrYy The F1 plant was made from fusing a gamete carrying RY and a gamete carrying ry Will the dominant alleles stay together or separate when making the F2 offspring?

Now cross these hybrid (RrYy) plants on a new 4X4 Punnett Square

What does the F2 cross tell us? Are there combinations of alleles that we did not see in either of the parents? This means that the alleles for seed color separated independently than the alleles for seed shape Genes that segregate separately do NOT influence each other’s inheritance

Steps for Dihybrid cross Make a Key Trait 1: height Dominant phenotype: Tall TT or Tt (ways to get it) Recessive phenotype: Short tt Trait2: color Dominant phenotype: Purple PP or Pp Recessive phenotype: White pp Write out genotypes for each parent _ _ _ _ x _ _ _ _ Write Out Gametes for each Parent (use arrows) 4 gametes for each parent (_ _) Make Punnett Square (16) boxes Label parent one and write gametes along top Label Parent 2 and write their gametes on side Fill in each box (should have 4 letters) Tally genotypes Write out 4 possible phenotypic combinations Dominant trait 1 and dominant for trait 2:______ Dominant trait 1 and recessive trait 2:_______ Recessive trait 1 and Dominant trait 2:_______ Recessive trait 1 and recessive trait 2:________ Tally Phenotypes (should =16) Write phenotypic ratio __dd__:__dr__:__rd__:__rr__ Dominant- capital letter D Recessive- lower case d Homozygous- 2 of the same size letter If its two little letters recessive dd If its 2 big letters it is dominant DD Heterozygous- 2 different size letters (capital and lowercase) Dd ALWAYS dominant

Principle of Independent Assortment Genes for different traits can segregate independently during the formation of gametes. This principle helps account for many genetic variations in plants, animals and other organisms.

Exception to Mendel’s Principles Incomplete Dominance (blending) Red flower + white flower= pink flower Co-Dominance Chicken with black and white feathers Multiple Alleles Many different possible alleles for 1 gene (blood type) Polygenic traits Traits controlled by many traits (eye color height)

Incomplete Dominance When red flowered (CRCR) plants were crossed with white flowered (CWCW) plants they made…pink flowers (CRCW) Which allele is dominant? neither Incomplete dominance: Case in which one allele is not dominant over another The heterozygous phenotype is somewhere between the two homozygous phenotypes

Codominance Both alleles contribute to the phenotype Chickens Allele for black feathers is codominant with allele for white feathers Chicken looks speckled with black and white feathers Not like the blending of dominant phenotypes… BOTH dominant phenotypes show up In humans Gene for protein that controls cholesterol levels in the blood People with heterozygous form make both types of protien

Multiple Alleles Genes for human blood type When a gene has more than two alleles NOT more than 2 alleles for a person but MORE than 2 alleles for the trait exist Coat color in rabbits A single gene for coat color At least 4 different alleles Simple dominance and make 4 possible coat colors Genes for human blood type 3 different alleles: IA, IB, I You can get different genotypes: IAIA IAi IAIB IBIB Ibi ii You can get different Phenotypes: Type A (dom) Type B (dom) Type AB (dom) Type O (recessive)

Polygenic Traits “Poly” many “-genic” genes Traits controlled by two or more genes Several genes interact to produce a trait Wide range of phenotypes Skin color Four different genes Fruit Fly eye color Three genes make the reddish brown pigment

Epistasis When the expression of one gene effects the expression of another gene Ex. Fur color in mice…controlled by 2 separate genes Gene 1 Brown fur pigment (BB or Bb) is dominant over gray fur pigment (bb) Gene 2 Coat Pigment depositing gene Dominant gene (CC or Cc) means fur will get pigment and this is determined by gene one Recessive gene (cc) means that no pigment will be deposited on fur…whether the they have the gene for black or brown fur The gene for Pigment Deposition is the EPISTATIC gene because it alters the Phenotypic ration Sd