Transcript Bb - Images
Warm-Up # 7 3/12/13 • In humans, brown eyes (B) are dominant over blue (b)*. A brown-eyed man marries a blue-eyed woman and they have three children, two of whom are brown-eyed and one of whom is blue-eyed. 1) What is the man’s genotype? 2) The woman’s genotype? 3) Draw the Punnett square that illustrates this marriage. 4) What are the genotypes of the children? Man’s genotype: Bb (Heterozygous Dominant) Woman’s genotype: bb (Homozygous recessive) Kid’s genotypes: 2-Bb (Heterozygous Dominant) 1-bb (Homozygous recessive) B b b b Bb bb Bb bb Independent Assortment, Dihybrid Crosses, and Beyond Dominant/ Recessive Ch 11-3 What’s This??? • Essential Question – How are independent assortment and dihybrids related? • Objectives – What is the principle of independent assortment? – What inheritance patterns exist aside from simple dominance? – Explain how Mendel’s principles apply to all organisms? Independent Assortment Review • Genes for different traits separate independently from one another when gametes are formed. • In order to come to the conclusion of independent assortment, Mendel did an experiment… Independent Assortment & 2Factor Crosses • Mendel followed 2 different genes. • It is called a two-factor (Dihybrid) cross. – Type of Punnett Square – 16 squares – Results: 9:3:3:1 (ratio) Dihybrid Crosses Example • Followed two traits • Gene for seed color and texture – Seed color………….Y=yellow, y=green – Seed texture……… R=round, r=wrinkled • They were dihybrid, meaning both traits were hybrids (heterozygous) • Let’s try one……… Dihybrid Cross – RrYy x RrYy F1 Gametes RY Ry rY ry RY RRYY RRYy RrYY RrYy Ry RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy 9 round-yellow: 3 round-green: 3 wrinkled-yellow: 1 wrinkled-green Mendel’s Results • Out of 556 seeds, he found – 315 were round and yellow – 108 were round and green – 101 were wrinkled and yellow – 32 were wrinkled and green • Guess what ratio this is??? 9:3:3:1 – 315: 108: 101: 32 ≈ _______ Mendel’s Conclusion • He concluded: Genes that separate independently DO NOT influence each other’s inheritance. (independent assortment) • Helps account for the many genetic variations When Heredity Follows Different Rules • Some alleles are neither dominant nor recessive. • Many are controlled by multiple alleles or multiple genes. Incomplete Dominance • Neither allele is completely dominant. • The heterozygous phenotype is a blend of the two homozygous phenotypes. • Ex: Red flower x white flower = pink flower. Codominance • Both alleles are ‘dominant’. • Both colors show at the same time. • Ex: black chicken x white chicken = black AND white chicken (NOT GRAY). Multiple Alleles • Many genes have more than 2 alleles. • The organism still gets ONLY 2 alleles for the trait. • Ex: rabbit color and human blood type. Human Blood Types Alleles = IA, IB, and i Blood types (phenotypes) = A, B, AB, O Phenotype (blood type) Genotype A IAIA or IAi B IBIB or IBi AB IA IB O ii Let’s Practice! • On the back of your notes, complete the following crosses and list offspring possibilities: 1) Mother has AB blood and Father has B blood (recessive) 2) Mother has AB blood and Father has B blood dominant. IA 1) IB IA IB IB IB IB MOM Outcome: 1 child with AB blood (IAIB) i IA i IB i 2 Children with B blood(IBIB, IBi) 1 Child with A blood (IAi) DAD 2) IB IA IB IA IB IB IB MOM Outcome: 2 children with AB blood (IAIB) IB DAD IA IB IB IB 2 children with B blood (IBIB) Multiple Alleles in Dogs • Labrador Retriever Genetics • Black is dominant to chocolate B or b • Yellow is recessive epistatic (when present, it blocks the expression of the black and chocolate alleles) E or e BBEE BbEE BBEe BbEe bbEE bbEe BBee Bbee bbee Albino Rabbit cc Full Color Rabbit CC, Ccch, Cch, or Cc Chinchilla Rabbit cchc, cchcch, or cchch Himalayan Rabbit chc or chch Polygenic Traits • • • • • Poly - many Genic - gene Traits controlled by 2 or more genes. Wide variety of phenotypes Ex: human skin color (controlled by >4 genes) and human eye color. Environmental Influence • Characteristics of an organism are determined by its genes AND its environment. • Ex: you may have the genes to be 6’ tall, but if you don’t have proper nutrition, you won’t be 6’! Let’s Practice! • On back of notes, complete the following cross: • F1 guinea pigs: male BbSs x female BbSs • B=black fur, b=brown fur S=short fur, s=long fur Dihybird Cross Practice • You will work with one parnter to complete the Dihybrid cross worksheet • Anything not finished today will need to be finished for homework tonight