Fundamentals of Genetics Chapter 11

Genetics The scientific study of heredity. Trait: a characteristic that can be passed from parent to offspring. Traits usually come in different forms. (i.e. Blue or brown eyes, tall or short, etc.)

Alleles Different forms of a gene. For example Blue or brown eyes. Blue = one allele. Brown = a different allele.

Genes Sections of a chromosome that code for a trait. For example Brown or blonde hair. Fish have fins, dogs have legs. Six fingers or five.

Dominant vs. Recessive Alleles When both a dominant and a recessive allele are present… Dominant allele: can be seen (expressed). Recessive allele: cannot be seen but is still present and may be seen in later generations.

Genotype and Phenotype Genotype: the genetic makeup of an organism. (What genes does it have?) Phenotype: The outward expression of a trait. (What you can see.) Bb or BB or bb = genotype Brown Brown Blue = phenotype

Homozygous vs. Heterozygous Homozygous: Same form of the gene from both parents. Homozygous recessive: bb or rr Homozygous dominant: BB or RR Heterozygous: Different forms of the gene from each parent. For example: Bb or Rr

Mendel’s Laws of Genetics Law of Segregation: Gene pairs separate when gametes form. Law of Independent Assortment: Genes separation is random and independent. Law of Dominance: A dominant allele will be seen and the recessive allele will be hidden.

What makes us unique? Sexual Reproduction Crossing over Mutations Genes from both parents Crossing over Swapping genes Mutations Random changes in genetic makeup Recombinations

Crossing-Over

Meiosis Meiosis I

Meiosis II Meiosis II Prophase II Metaphase II Anaphase II Telophase II Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. The chromosomes line up in a similar way to the metaphase stage of mitosis. The sister chromatids separate and move toward opposite ends of the cell. Meiosis II results in four haploid (N) daughter cells.

Gregor Mendel (1822-1884) 1860’s did experiments with pea plants. Conducted experiments that established modern genetics.

Gregor Mendel Chose peas because they had seven traits that were unusual. Each trait only had two forms. Tall or short Purple or white Yellow or green

Purebred Mendel’s peas could self-fertilize. Purebred: the offspring receives the same trait from both parents. Hybrid: the offspring receives different forms of the trait from each parent.

Principles of Dominance Section 11-1 P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short

Mendel’s Seven F1 Crosses on Pea Plants Seed Shape Seed Color Seed Coat Color Pod Shape Pod Color Flower Position Plant Height Round Yellow Gray Smooth Green Axial Tall Wrinkled Green White Constricted Yellow Terminal Short Round Yellow Gray Smooth Green Axial Tall

Chromosomal Theory of Heredity States that the material of inheritance is carried by genes on the chromosomes. Walter S. Sutton proposed the theory in 1903.

What are the chances? Can be expressed as… Fractions: 1/3 Percentages: 33% Ratios: 1:2

Punnett Squares Show the probabilities… are not guaranteed. Monohybrid Cross: studying one trait at a time. Dihybrid Cross: studying two traits at a time. Test Cross: a monohybrid cross in which one of the parents is homozygous recessive. This cross reveals hidden alleles.

Monohybrid Cross Tt Parent 1 T t T T T T t Parent 2 TT T T T T t

Probabilities P(1) x P(2) x P(3) = Total Probability Example Tt x TT Hh x hh Ww x Ww What the chance of having offspring with the following genotype Tthhww

TtGg ttGg Dihybrid Cross Parent 1 T G T g t G t g t G T t G G TtGg

rr Test Cross r r RR R R r R r Rr ? ? r ? r Parent 1 Homozygous recessive r r Parent 2 RR R R r R r or Can roll Can roll Rr ? ? r ? r Tongue Roller Can roll Can roll

Autosome and Sex-Linked Autosomal- Genes or traits found on any chromosome except sex chromosome Sex-Linked- genes or traits found on the sex chromosomes

Figure 14-13 Colorblindness Section 14-2 Father (normal vision) Normal vision Colorblind Male Female Daughter (normal vision) Son (normal vision) Mother (carrier) Daughter (carrier) Son (colorblind)

Exceptions to the dominant recessive rule. Incomplete Dominance: offspring show an intermediate form of the trait. Codominance: offspring show both forms of the trait. Polygenic Traits: traits that are controlled by two or more genes. Multiple Alleles: three or more alleles control a trait. Pleiotropy: one gene affects more than one trait.

Examples of the exceptions... Incomplete Dominance: red and white colored flowers have offspring with pink flowers. Codominance: Human blood type (A, B, AB, O). Polygenic Traits: Human eye color. Multiple Alleles: Human hair color. Pleiotropy: Sickle-cell anemia disease.

Incomplete Dominance in Four O’Clock Flowers

Blood Groups Safe Transfusions Phenotype Antigen on (Blood Type Red Blood Cell Genotype To From

Pedigree A chart that shows how a trait is inherited within a family. Carriers Phenotype Bb bb Bb Bb Bb bb Bb Genotype bb

Pedigree Figure 14-3 A Pedigree Section 14-1 A circle represents a female. A square represents a male. A horizontal line connecting a male and female represents a marriage. A vertical line and a bracket connect the parents to their children. A half-shaded circle or square indicates that a person is a carrier of the trait. A circle or square that is not shaded indicates that a person neither expresses the trait nor is a carrier of the trait. A completely shaded circle or square indicates that a person expresses the trait.

Identifying types of inheritance by pedigree charts Autosomal-trait appears in both sexes X-linked-trait appears in only one sex Dominant- no carriers are shown Recessive- carriers are present Four types Autosomal dominant, autosomal recessive, x-linked dominant, x-linked recessive

The Cause of Cystic Fibrosis Chromosome # 7 CFTR gene The most common allele that causes cystic fibrosis is missing 3 DNA bases. As a result, the amino acid phenylalanine is missing from the CFTR protein. Normal CFTR is a chloride ion channel in cell membranes. Abnormal CFTR cannot be transported to the cell membrane. The cells in the person’s airways are unable to transport chloride ions. As a result, the airways become clogged with a thick mucus.

Genes can react to the environment Body temperature causes a rabbit to have black or white fur. Soil acidity determines blue or pink flowers. Japanese goby fish will change from female to male and back again. Human height.

Gene Therapy Bone marrow cell Normal hemoglobin gene Nucleus Chromosomes Bone marrow Genetically engineered virus