H EREDITY AND M ONOHYBRID C ROSSES Mendel’s Experiments Homozygous/Heterozygous Genotype/Phenotype Dominant/Recessive Incomplete Dominance/Codominance Punnett Squares

G ENETICS & H EREDITY genetics study of heredity and the variations of inherited traits heredity passing of traits from parents to offspring

G ENETICS B EFORE M ENDEL some scientists believed that traits from parents are blended together to produce offspring ex – a tall parent and a short parent would produce an average child observation allowed other scientists to notice that offspring sometimes exhibited traits identical to that of only one parent ex – a brown eye parent and a blue eye parent produce a brown eye child

G REGOR M ENDEL monk father of genetics studied pea plants to determine how traits where passed on from one generation to the next

W HY USE PEA PLANTS ? flowers have both male and female reproductive organs plants can be self pollinated or cross pollinated have many traits that can be observed

M ENDEL ’ S E XPERIMENT crossed/mated two true breading plants (plants that produce offspring that are genetically identical to the parent) when P generation (parent plants) plants were crosses all offpsring (F 1 generation) displayed the same trait when two F 1 generation plants were crosses to produced offspring (F 2 generation) traits were repeated in a ratio of 3:1

M ENDEL ’ S E XPERIMENT

M ENDEL ’ S C ONCLUSIONS Law of Segregation for each characteristic (trait) and organism carries two factors (genes), one from each parent parent organisms donate only one copy of each factor (gene) in their gametes (sex cells) during meiosis the two factors (genes) are separated

H OMOZYGOUS /H ETEROZYGOUS homozygous individual that carries two of the same alleles for a given characteristic/trait ex – two blue eyed genes (bb), two brown eyed genes (BB) heterozygous individual that carries two different alleles for a given characteristic/trait ex – one blue eyed gene and one brown eyed gene (Bb)

G ENOTYPE /P HENOTYPE genotype genetic makeup of an individual ex – an individual carries one blue eyed gene and one brown eyed gene (Bb) phenotype outward appearance of the individual ex – an individual has brown eyes

D OMINANT /R ECESSIVE dominant allele allele that is always expressed (seen) if it is present represented by a capital letter in genotype ex – brown eye allele (B) recessive allele allele that is expressed only if the dominant allele is not present individual must be homozygous for the recessive allele represented by a lower case letter in genotype ex – blue eye allele (b)

C OMPLETE AND I NCOMPLETE D OMINANCE complete dominance only one allele is expressed one allele determines the phenotype of the individual incomplete dominance neither allele is dominant over the other both alleles are expressed phenotype of the individual is a result of both alleles

C ODOMINANCE both alleles are expressed fully offspring with both alleles show a third phenotype ex – red bull and white cow produce roan calves (have both pure white hair and pure red hair)

B LOOD T YPES – C ODOMINANCE AND D OMINANCE blood types show both codominance and dominace three alleles are present type A allele – I A type B allele - I B type O allele - i type A and B blood alleles are codominant (both are expressed if an individual carries both) type A blood alleles are dominant over type O blood alleles (individual will express type A blood) type B blood alleles are dominant over type O blood alleles (individual will express type B blood)

B LOOD T YPES – C ODOMINANCE AND D OMINANCE

P UNNETT S QUARE Q UESTIONS diagram used to predict genotype and phenotype of offspring dominant genes are represented by a capital letter and recessive genes are represented by a lowercase letter Example 1 In pea plants, the allele for yellow seed colour, Y, is dominant over that for green seed colour, y. Consider a cross between a pea plant that is homozygous for yellow seeds and a plant that is homozygous for green seeds. Determine the possible genotypes and phenotypes of the offspring.

P UNNETT S QUARE Q UESTIONS Example 2 Two heterozygous yellow seed plants (Yy) are crossed. Determine the genotype and phenotype of the offspring.

P UNNETT S QUARE Q UESTIONS Example 4 A researcher crossed a homozygous yellow seed plant (YY) and a heterozygous yellow seed plant (Yy). Determine the genotype and phenotype ratios of the offspring.

P UNNETT S QUARE Q UESTIONS Example 5 A farmer crossed a heterozygous yellow seed plant with a recessive green seed plant. Determine the genotype and phenotype of the offspring.

P UNNETT S QUARE Q UESTIONS incomplete dominance and codominance are represented by a capital letter and a superscript letter Example 6 Snapdragons are coloured based on two alleles that show incomplete dominance, white (C W ) and red (C R ). What are the genotypes and phenotypes of the F 1 and F 2 generations?

P UNNETT S QUARE Q UESTIONS Example 7 William and Kate have three children. Their blood types are AB, O and A. What are the genotypes of each child? What are the genotypes and phenotypes of William and Kate?