Transcript Genetics
Genetics The study of Heredity Mendel and His Peas Gregor Mendel 1860’s monk that discovered the fundamental principles of genetics by breeding garden peas. Mendel crosspollinated pea plants He cut away the male parts of one flower, then dusted it with pollen from another Mendel’s Conclusions He concluded that factors are passed from one generation to the next. Genes and Alleles Genes Sequence of DNA that codes for a protein and determines a trait. Alleles Alternate forms of genes. One comes from your mom and one from your dad. Dominant and Recessive alleles Dominant alleles – represented by upper-case letters (B) trait will always appear, only one dominant allele needed. (BB or Bb) Recessive alleles – represented by lower case letters(b) trait will not appear UNLESS both recessive alleles are present (bb). Recessive traits show up about 1/4th of the time. Because there is only a 25% chance that two recessive alleles will be paired together. eye color locus B = brown eyes The Principle of Dominance Some alleles are dominant and others are recessive. Paternal Maternal Recessive alleles are not expressed in the organism, but may be passed on to future generations. eye color locus b = blue eyes Types of Allele pairing Homozygous (purebred) both alleles are the same (BB – Brown eyes) (bb – blue eyes) Heterozygous (hybrid) two different alleles (Bb – Brown eyes) Phenotype Outward appearance Physical characteristics Examples: 1.Brown eyes 2.blue eyes Genotype Arrangement of genes that produces the phenotype Example: 1. BB, Bb 2. bb Punnett Square A Punnett square is used to show the possible combinations of gametes and allow us to determine the probability of an allele combination. Monohybrid Cross Example: Cross between two heterozygotes brown eyes (Bb) BB = brown eyes Bb = brown eyes bb = blue eyes B B b BB Bb Bb bb Bb x Bb b female gametes male gametes Monohybrid Cross BB= homozygous dominant; 1 of 4 = 25% Bb= heterozygous dominant; 2 of 4 = 50% bb= homozygous recessive; 1 of 4 = 25% Chances of Brown Eyes: 3 of 4 = 75% Chances of Blue Eyes: 1 of 4 = 25% B b B BB Bb b Bb bb Bb x Bb Dihybrid Cross: RrYy x RrYy CROSSES WITH TWO DIFFERENT TRAITS Here’s your game plan: FIRST: FOIL the alleles just like you do for polynomials in math class (Rr) (Yy) x (Rr) (Yy) First: RY RY Inner: rY rY Outer: Ry Ry Last: ry ry Dihybrid Cross: RrYy x RrYy SECOND: take your results from your FOILing and place them on the sides of your Punnett square! Add like letters to like letters in the boxes. RY RY Ry rY ry RRYY Ry rY ry Dihybrid Cross RY RY RRYY Ry Ry RRYy rY RrYY ry RrYy Smooth/Yellow: 9 of 16 Smooth/green: 3 of 16 RRYy RRyy RrYy Rryy wrinkled/Yellow: 3 of 16 rY RrYY RrYy rrYY rrYy wrinkled/green: 1 of 16 ry Rryy rrYy rryy 9:3:3:1 phenotypic ratio RrYy Incomplete Dominance One allele is not completely dominant over another and the traits combine, or blend R R W RW RW W RW RW Incomplete Dominance W W R R RW RW RW RW a. List the possible genotypes and phenotypes genotypes – RW phenotypes – Pink b. How many of the plants would have red flowers? 0% c. How many would have white flowers? 0% d. How many would have pink flowers? 100% Codominance Black cow + white cow = spotted cow Blood Types: A, B, AB, O Codominance Example: Both alleles are expressed Example: blood 1. 2. 3. 4. type A type B type AB type O = = = = IAIA or IAi IBIB or IBi IAIB ii Blood Type O (ii) X Blood Type A (IAIA ) i i IA IA i IA i IA IA i IA i Codominance GENOTYPE IAIA = ______ of ______=____% = Type________ IAi = 4 of 4 = 100% = Type A blood IBIB = ______ of ______=____% = Type________ IBi = ______ of ______=____% = Type________ IAIB = ______ of ______=____% = Type________ ii = ______ of ______=____% = Type________ Karyotype Analysis To analyze chromosomes, we cut up and assemble photographs of chromosomes in pairs. There are 44 autosomal chromosomes and 2 sex chromosomes in humans.