Mendel Genetics and Punnett Squares Origin of Genetics Steps of a Monohybrid cross Terminology Practice Punnett Squares Determining Unknown Genotypes
The Origin of Genetics Heredity- the passing of characteristics from parents to offspring Genetics- the branch of Biology that focuses on heredity Cross- combining traits from two parents by breeding (sexual reproduction)
The Origin of Genetics Gregor Mendel –Austrian monk –Studied theology, science and mathematics –Noticed patterns in the pea plants he was growing –Mendel crossed pea plants and studied the genetic turn-outs –Was the first to develop rules that accurately predict patterns of heredity –Father of genetics
The Origin of Genetics Monohybrid cross- a cross that involved one pair of contrasting traits Ex. Crossing a white flower with a purple flower.
Steps of a Monohybrid cross 1.Ensure each variety is true-breeding for a particular characteristic Ex. A true-breeding purple flower will produce only purple flowers These are the 1 st two individuals crossed - P generation (parental generation)
Steps of a Monohybrid Cross 2. Cross-pollinate two P-generation plants Ex. A true breeding purple flower crossed with a true-breeding white flower The offspring are called F1 generation (filial generation)
Steps of a Monohybrid Cross 3. Self-pollinate the F1 generation to create the F2 generation (second filial generation) –This creates a 3:1 ratio True breeding P generation F1 generation F2 generation Self pollinate Cross Self pollinate
Terminology Alleles- alternative versions of genes –The gene for hair color can have multiple alleles (blonde hair allele, brown hair allele, etc) Dominant- the expressed (visible) trait Recessive- the trait that is not expressed or observable
Terminology Homozygous- when two alleles of a particular gene are the same –(PP), (pp), (RR), (rr), (VV), (vv), etc Heterozygous- when two alleles of a particular gene are different –Only the dominant allele is expressed while the recessive is present, but not expressed –(Pp), (Rr), (Vv), etc
Terminology Genotype- the set of alleles an individual has for a trait –think “genes” and “letters” –(Rr), (RR) or (rr) –(Vv), (VV) or (vv) Phenotype- the physical appearance of a trait –Think “face” and “colors” –White, purple, red, blonde, freckles, blue eyes, etc
Practice (assume that P is purple and p is white) (Pp): What is the genotype? What is the phenotype? Is it homozygous or heterozygous?
Practice (assume that P is purple and p is white) (pp): What is the genotype? What is the phenotype? Is it homozygous or heterozygous?
Practice (assume that P is purple and p is white) (PP): What is the genotype? What is the phenotype? Is it homozygous or heterozygous?
Punnett Squares Punnett square- is a diagram that predicts the outcome of a genetic cross by considering all possible combinations
Punnet Squares Ex. Having freckles (F) is dominant to not having freckles (f). Parent 1 is heterozygous for freckles and Parent 2 is also heterozygous Parent 1 Parent 2 F FFFF F f f f fff Phenotype ratio? 3:1
Punnett Squares Box 1 is homozygous for…. Box 2 and 3 is….. Box 4 is…. F FFF F F f f f fff 12 34
Punnett Squares Ex. A homozygous yellow pea plant (Y) is dominant over a homozygous green pea plant (y). YY y y Y Y Y Y yy y y What’s the genotype of all offspring? What’s the phenotype of all offspring? Yy yellow What’s the phenotypic ratio? 4:0
Determining Unknown Genotypes When a phenotype is dominant but the genotype is not known, a test cross is performed. –You cross the unknown genotype with a homozygous recessive individual
Determining Unknown Genotypes What does that mean? You can physically see that the pea plant is yellow, but you don’t know if they are (YY) or (Yy). So, you cross the yellow pea plant with a recessive pea plant (yy) that is green. If the offspring are all yellow the genotype is (YY) If the offspring are ½ yellow and ½ green the genotype is (Yy)
Determining Unknown Genotypes Doesn’t make sense? Use the Punnett Square and work backwards! Known, recessive genotype Unknown genotype yy Y ???