Genetics How Traits are Passed from Parents to Offspring

I.Gregor Mendel and his pea plants A. Studied how traits were passed from parent to offspring in pea plants 1. Why did he study pea plants? *Large number of offspring *7 easily seen traits (flower color, height, seed color, seed texture, pod color, pod appearance, flower location)

2. Observations from pea plants: * Created pure bred pea plants for a particular trait (always produced offspring with that trait) Example: If two pure bred purple plants were crossed you would end up with…. Purple X Purple = all purple offspring (100%) X = Pure bred plants are called the P1 generation

* Performed specific test crosses Example: What would happen if a pure bred white flower was crossed with a pure bred purple flower? Purple (P1) X White (P1)= all purple offspring (100%) X = What if we crossed 2 of the offspring from this cross? P1 F1

Let’s Try It! F1 Purple X F1 Purple = 75% Purple and 25% White X = F1 F2

B. Mendel’s Conclusions (4)

1. Traits are controlled by 2 factors (genes) Gene for eye color from mom Gene for eye color from dad Offspring receives 2 genes for each trait – one from each parent

2. There are dominant and recessive genes Pure Purple Flower X Pure White Flower X PP pp All offspring are purple because the P is dominant over the p Pp

3. Law of Segregation: genes separate during meiosis (gamete production) *So, you have one copy of each gene in the sperm and one copy of each in the egg

4. Law of Independent Assortment: genes for different traits are distributed into gametes randomly

C. Vocabulary: Genetics: study of heredity Genetics: study of heredity Heredity: the passing on of traits from parents to offspring Heredity: the passing on of traits from parents to offspring Trait: a specific characteristic (eye color) Trait: a specific characteristic (eye color) Gene: factors that are passed on from one generation to the next Gene: factors that are passed on from one generation to the next Allele: different forms of a gene (blue vs. brown) Allele: different forms of a gene (blue vs. brown) Dominant Allele: gene that will mask the recessive allele Dominant Allele: gene that will mask the recessive allele Recessive Allele: not seen if dominant allele is present Recessive Allele: not seen if dominant allele is present Genotype: alleles present for a certain gene Genotype: alleles present for a certain gene * Homozygous Dominant: both alleles are dom. (TT) * Homozygous Recessive: both alleles are rec. (tt) * Heterozygous: one allele is dom. and one is rec. (Tt) Phenotype: the physical characteristic shown from the genotype Phenotype: the physical characteristic shown from the genotype

True-Bred or Pure Bred: an organism who will always produce offspring identical to themselves True-Bred or Pure Bred: an organism who will always produce offspring identical to themselves P1: parental generation P1: parental generation F1: offspring from P1 F1: offspring from P1 F2: offspring from F1 F2: offspring from F1 Law of independent assortment: homologous chromosomes arrange themselves randomly during meiosis 1 Law of independent assortment: homologous chromosomes arrange themselves randomly during meiosis 1 Law of segregation: homologous chromosomes separate during meiosis 1 Law of segregation: homologous chromosomes separate during meiosis 1 Probability: the likelihood of an event occurring Probability: the likelihood of an event occurring Monohybrid cross: cross that involves one trait Monohybrid cross: cross that involves one trait Dihybrid cross: cross that involves 2 traits Dihybrid cross: cross that involves 2 traits Punnett Square: used to predict offspring Punnett Square: used to predict offspring Genotypic Ratio: ratio of homozygous dominant: heterozygous: homozygous recessive Genotypic Ratio: ratio of homozygous dominant: heterozygous: homozygous recessive Phenotypic Ratio: ratio of dominant trait: recessive trait Phenotypic Ratio: ratio of dominant trait: recessive trait Complete Dominance: in the heterozygous form, only the dominant trait is expressed Complete Dominance: in the heterozygous form, only the dominant trait is expressed Incomplete Dominance: in the heterozygous form, there is an in between trait Incomplete Dominance: in the heterozygous form, there is an in between trait Codominance: in the heterozygous form, both traits are expressed Codominance: in the heterozygous form, both traits are expressed

II. Punnett Squares A. Used to predict all possible offspring 1. Dad’s genes on top, mom’s on the left 2. Fill in squares to determine possible offspring *Example: What are the chances of having a boy? What can dad give? What can mom give? XY X X XXXY XXXY 50% chance of having a boy

What would you get if you crossed a homozygous purple flower with a homozygous white flower? *First you must figure out what the genes for the “parents” are. Homozygous purple= Homozygous white= PP pp * Second, place the genes on a punnett square and fill P P p p Pp

Third: write the ratios (genotypic and phenotypic) Genotypic Ratio Homozygous Dominant (PP): Heterozygous (Pp): Homozygous Recessive (pp) PpPp PpPp PP p p 0:4:00:4:0

Phenotypic Ratio Dominant Trait: Recessive Trait PpPp PpPp PP p p 4 : 0

Now you set up the following test cross and solve for the ratios Cross a homozygous purple flower with a heterozygous purple flower.

PPPP PpPpPpPp PpPpPpPp P P p Geno. Ratio 2:2:0 Pheno. Ratio 4:0

Now you set up the following test cross and solve for the ratios Cross two heterozygous tall plants

TTTt Tttt TtTt T t Geno. Ratio 1:2:1 Pheno. Ratio 3:1

Dihybrid Cross: cross involving 2 traits Homozygous green wrinkled seed Genotype: yyss Heterozygous yellow, Heterozygous smooth seed Genotype: YySs *Now we must find all possible combinations for each parent plant Seed color: Y=yellow, y=green Seed texture: S= smooth, s=wrinkled

Parent #1: yyss ys ys ys ys ys

Parent #2: YySs What are all of the possible allelic combinations from this parent? YS, Ys, yS, ys ys ys ys ys YS Ys yS ys Now fill in the chart!

YySsYySsYySsYySs Yyss?YyssYyss yySsyySs?yySs yyss?yyssyyss ys ys YS Ys yS ys

III. Types of Dominance A. Complete dominance: one trait is completely dominant over another (Rr= Red) B. Incomplete Dominance: heterozygous offspring will have a phenotype in between the dominant and recessive trait (Rr= pink) C. Codominance: heterozygous offspring show both traits (Rr= red and white hair)

Incomplete Dominance

Codominance