Genetics Monohybrid Cross Six Key Terms in Heredity

Genetics Monohybrid Cross

Six Key Terms in Heredity 1. Homozygous: • Homo: same • Zygote: fertilized egg • refers to an individual with two identical alleles for a trait • ex: AA or aa

Six Key Terms in Heredity 2. Heterozygous • Refers to an individual with two different alleles for a trait • Hetero: different • ex: Aa

Six Key Terms in Heredity 3. Genotype • “genes” (cannot see) • The genetic makeup of an organism as indicated by its set of alleles • ex: AA, Aa, or aa

Genotype Example Female Male Dominant A a Recessive allele. Genotype allele

Six Key Terms in Heredity 4. Phenotype • “P” for physical appearance • The observable characteristics of an organism • ex: eye shape, nose shape, or skin color

Six Key Terms in Heredity 5. Dominant • Represented by upper case letters • Opposite of recessive • The genetic trait that is expressed when its allele is homozygous or heterozygous • ex: A

Six Key Terms in Heredity 6. Recessive • Represented by lower case letters • Opposite of dominant • The genetic trait that is not expressed when the contrasting form of the trait is present • ex: a

Combination of terms Genotype AA Homozygous Dominant Aa Heterozygous aa Homozygous Recesive

Genotype determines phenotype Dominant B = Blue recessive b = white Blue BB Genotype Blue White Bb White bb Phenotype

Monohybrid Cross • Mono: means one • Hybrid: mixed origin: crossbreeding Definition: a cross between individuals regarding only one trait

Punnett Square • A tool used to aid in the prediction of outcomes in the cross

How to Use a Punnett Square • We must first determine the possible gametes the parents can give • These possibilities are then placed around the square Tt Tt

Genotype Ratio • The ratio (how many) of the genotypes that appear in the offspring

Genotype Ratio • Place in order • Homozygous dominant: heterozygous: homozygous recessive TT : Tt : tt 1 : 2: 1

What is the genotype ratio? • AA x aa • 0: 4: 0 A A • 0: 1: 0 a Aa Aa • 1: 0

What is the genotype ratio? • Aa x aa • 0: 2: 2 A a • 0: 1: 1 a Aa a a • 1: 1

Phenotype Ratio • the ratio (how many) of phenotypes that appear in the offspring Brown : White 4 : 0 1 : 0

How can you determine their genotype?

Testcross • Cross an unknown genotype (AA or Aa) with a homozygous recessive • Look at the offspring to determine the genotype of the unknown parent

Types of Inheritance • Complete Dominance • Incomplete Dominance • Codominance

Complete Dominance FF : Ff : ff Freckles: No Freckles • One allele complete dominates over the other and “masks” it • ex: freckles

Incomplete Dominance • Two or more alleles influence the phenotype • Intermediate: “blend/mix” • ex: four o’clock RR : Rr : rr Red : Pink : White (flowers)

Codominance RR : Rr : rr Red : Roan : White • Both alleles are equally expressed • Neither allele is dominant or recessive • ex: Roan (red and white hair)

Review: Types of Inheritance Complete Dominance R = Red r = white Red RR • Note: Only the heterozygous is affected Red White Rr White rr Phenotype

Review: Types of Inheritance Incomplete Dominance R = Red r = white Red RR • Note: Only the heterozygous is affected Red White Rr White rr Phenotype

Review: Types of Inheritance Codominance R = Red r = white Red RR • Note: Only the heterozygous is affected Red White Rr White rr Phenotype

Helpful Hints • If you encounter a problem that has only two phenotypes, it is an example of complete dominance • If you encounter a problem that has three phenotypes, determine if it is incomplete dominance or codominance – Look at the heterozygous genotype (Is it mixed/blended or are both alleles expressed? )

Blood: Multiple Alleles and Codominance • Multiple alleles: more than two alleles • Two dominant alleles and a recessive allele • Dominant Alleles – IA (Type A allele) – IB (Type B allele) • Recessive Allele – i (Type O allele)

Blood Types • Type A Blood – IAIA (homozygous) • (AA) – IAi (heterozygous) • (AO)

Blood Types • Type B Blood – IBIB (homozygous) • (BB) – IBi (heterozygous) • (BO)

Blood Types • Type AB Blood – IAIB (codominance) • Two dominant alleles • (AB) – Universal Receiver

Blood Types • Type O Blood – ii (homozygous recessive) • (OO) – Universal Donor

Practice • Can Parents with Blood Type A and Blood Type B give birth to a child with Blood Type O? A I i B I A B I I B I i i A I i ii Yes (Heterozygous Type A x Heterozygous Type B)