Mendel & Inheritance SC.912.L.16.1 Use Mendel s laws of segregation and independent assortment
Mendel s Law of Segregation: gene pairs separate when gametes (sex cells) are formed; each gamete as only one allele of each gene pair Review: Heterozygous = the two alleles are different (hybrid) Aa or Bb Homozygous = the two alleles are the same (AA or aa)
Mendel s Law of Independent Assortment: different pairs of genes separate independently of each other when gametes are formed This means when chromosomes line up in homologous pairs during Metaphase I of meiosis that not ALL of moms chromosomes are on one side and not ALL of dads chromosomes are on one side THEY ARE INTERMIXED!
Dominant Traits: shown with capital letters; controlling trait Example: Brown hair over blonde hair; Huntington s disease Recessive Traits: shown with lowercase letters; hidden allele Examples: Cystic fibrosis and Tay Sach s can be a carrier OR must have two recessives for it be expressed
Inheritance can be predicted using a Punnett square Results show the probability of an offspring receiving that trait, and may be expressed in percent, ratios, or fractions Genotype probability (genetic makeup of the organism): TT 25%, ¼, or 1:4 Tt 50%, ½, or 2:4 (1:2) Tt 25%, ¼, or 1:4
Practice predicting Punnett square results. Express results for both genotype and phenotype (physical appearance of an organism)
Two Types of Crosses: Monohybrid: Contains four boxes; a cross between two heterozygous would produce a 1:2:1 genotype ratio and a 3:1 phenotype ratio Dihybrid: Contains sixteen boxes; a dihybrid cross involves two traits for each parent and a cross between two heterozygous parents would produce a 9:3:3:1 phenotype ratio
Dihybrid Cross:
2. Student s will identify, analyze, and/or predict inheritance patterns cause by various models of inheritance. Patterns of Inheritance: Sex Chromosomes: 23 pairs, XY = males, XX = females Sex-Linked Traits: traits linked with particular sexes, X-linked traits are on inherited on X chromosome from mother (examples: hemophilia, color-blindness, baldness) Multiple Alleles: presence of more than two alleles for a trait (eye color) Polygenic Trait: one trait controlled by many genes (hair color, skin color); genes may be on the same chromosome or different chromosomes
2. Student s will identify, analyze, and/or predict inheritance patterns cause by various models of inheritance. Patterns of Inheritance (Continued): Codominance: phenotypes of both homozygous parents are produced in heterozygous offspring so both alleles are expressed (black + white chickens = checkered chicken; sickle cell anemia) Incomplete Dominance: phenotype of a heterozygote is a mix of the two homozygous parents; neither allele is dominant, but combine to display both traits (white flower + red flower = pink flower)
2. Student s will identify, analyze, and/or predict inheritance patterns cause by various models of inheritance. A pedigree may be used to show patterns of inheritance squares = males and circles = females shaded = affected, halfshaded = carrier