The Living Environment

1. The Living Environment The study of organisms and their interactions with the environment.

2. Topics • Unit 1: Ecology • Unit 2: The Cell • Unit 3: Genetics • Unit 4: History of Biological Diversity • Unit 5: The Human Body

3. GENETICS The science of heredity and the study of how traits are passed on from generation to generation.

4. Mendelian Genetics: How Genetics Began • Commonly referred to as the “father of modern genetics” Gregor Mendel, born in 1822 in what is now the Czech Republic, published the first known findings of heredity in 1866. • His primary findings were based on the study of pea plants during his 14 year tenure as an Austrian monk in charge of the monastery garden.

5. Mendelian Genetics • While tending his plants, Mendel was intrigued by the pea plants because he noticed that some were tall while others were short; some had white flowers and some had purple flowers; some had green peas and others had yellow peas. • Mendel was determined to try to figure out what determined these different traits as well as others and began experimenting.

6. Plant Sexual Reproduction • Pollen, produced by the anther, is transferred to the stigma, travels down the style into the ovary, and fertilizes the ovule producing a seed. • Self-pollination occurs when pollen is transferred to the stigma of the same plant. • Cross-pollination occurs when pollen is transferred to the stigma of another plant.

7. Mendelian Genetics • Mendel began cross pollinating plants with similar traits and plants with varying traits and recording the outcomes of these crosses in a journal. • From these various crosses performed over many years, Mendel concluded that traits are passed on from one generation to the next and wrote three laws regarding his findings.

8. Mendelian Genetics • The Law of Dominance states that certain traits exhibit dominance over others which are said to be recessive. • In other words, if two different alleles of the same trait are combined to form offspring, all of the offspring will exhibit the dominant allele. • The only way for the offspring to express the recessive allele would be for both inherited alleles to be the recessive form of the trait.

9. Mendelian Genetics • The Law of Segregation, later proven by the discovery of the process of meiosis, states that each gamete, produced by each parent, receives only one allele of each trait; thus the alleles of each trait are segregated amongst the gametes. • In other words, each sperm and egg produced only carries one allele for each trait resulting in offspring who receive one allele of each trait from each parent.

10. Review of Meiosis • Recall that meiosis results in four daughter cells each containing half the number of chromosomes as the original cell and half the alleles of each gene. • These daughter cells are also genetically different from the parent cell and from each other due to cross-over that occurs during prophase of meiosis I.

11. Mendelian Genetics • The Law of Independent Assortment states that traits are inherited independently of each other. • For example, with Mendel’s pea plants, the trait for plant height is inherited separately from the trait for pea color or flower color. • This law does not apply to all traits in all organisms as some traits are genetically linked and are inherited together.

12. Probability and Punnett Squares • A genotype is a pair of letters representing a particular genetic makeup, or type of genes. These letters are chosen based on the dominant allele. • A phenotype is the physical characteristic exhibited by the organism as a result of its genotype. • An organism’s phenotype is dependant on its genotype.

13. Probability and Punnett Squares • A homozygous pair of alleles is represented by any two of the same letters, either both capital or both lowercase. This is known as a purebred trait, where both alleles are identical. • It is possible for a homozygous trait to be dominant or recessive. • A heterozygous pair of alleles is represented by two different letters, one capital and one lowercase. This is known as a hybrid trait and will always exhibit the dominant phenotype.

14. Probability and Punnett Squares • In the early 1900’s Dr. Reginald Punnett developed the Punnett Square to predict the possible offspring of a cross between two known genotypes. • Mendel’s journals show that even he was able to produce the ratios of offspring that we can now easily calculate using Punnett Squares.

15. Probability and Punnett Squares • A monohybrid cross is a cross involving hybrids of a single trait. • A monohybrid cross of the F1 generation will always result in 75% of the offspring exhibiting the dominant trait. • A monohybrid cross results in a genotypic ratio of 1:2:1 and a phenotypic ratio of 3:1.

16. Probability and Punnett Squares • A dihybrid cross is a cross involving hybrids of two different traits at the same time using a single Punnett Square. • A dihybrid cross results in a genotype and phenotypic ratio of 9:3:3:1. • Dihybrid crosses can be used to prove Mendel’s Law of Independent Assortment.

17. Incomplete Dominance • Cases in which one allele is not completely dominant over another are called incomplete dominance. • These traits are sometimes referred to as “blending” traits. • Examples include pink carnations and palomino horses.

18. Examples of Incomplete Dominance +=

19. Codominance • Codominance occurs when both alleles (from each parent) contribute to the phenotype of the offspring because neither is dominant. • Codominance results in a heterozygous (hybrid) organism such as a roan cow which has both red and white hairs.

20. Polygenic Traits • Traits controlled by two or more genes are called polygenic traits. • Polygenic traits often result in a wide range of phenotypes such as the range of eye colors or the range of skin tones in humans.

21. The Discovery of DNA • Although Mendel’s journals were discovered around the turn of the 20th century, scientists lacked the technology to perform genetic research in any greater detail than Mendel himself until about 1940. • In 1944, Oswald Avery and his team determined that genes were composed of biochemical molecules called DeoxyriboNucleicAcid (DNA).

22. DNA as a Double Helix • In 1951, Linus Pauling and Robert Corey determined that proteins like those found in the DNA molecule were a helical type of structure. • In 1952, Rosalind Franklin using a technique called X-Ray diffraction took a “picture” of the DNA molecule. • In 1953, James Watson and Francis Crick developed the double-helix model of the structure of DNA.

23. DNA – The Double-Helix • DNA, sometimes referred to as a twisted ladder or spiral staircase, is a very long chain molecule, consisting of sub-units called nucleotides. • Each nucleotide is made up of three basic structures: • A sugar called deoxyribose • A phosphate group • A nitrogenous base

24. DNA Structure • The backbone of the DNA structure, or side rails, are formed by the sugar-phosphate groups of each nucleotide. • Connecting the two rails of the DNA structure are four types of nitrogenous bases: • Thymine (T) • Adenine (A) • Cytosine (C) • Guanine (G)

25. DNA Structure • The side rails of the twisted ladder are attached by the pairing of the nitrogenous bases extending from each side of the DNA molecule, creating the rungs of the ladder. • Adenine always pairs with Thymine, while Guanine always pairs with Cytosine, thus creating the base pairs: • A – T • G – C

26. DNA Structure

27. Chromosome Structure • Chromosomes consist of tightly packed coils of DNA called chromatin. • Chromatin consists of a DNA molecule tightly wound around proteins called histones. • DNA consists of nucleotides which code for individual genes. • Chromosome Chromatin DNA Gene Largest Smallest • Chromosome Chromatin DNA Nucleotide

28. DNA Replication • During DNA replication, the DNA molecule separates into two strands, then produces two new complimentary strands following the rules of base pairing. • Each strand of the double-helix serves as a template for the new strand.

29. DNA Replication • DNA replication is carried out by a series of enzymes. • These enzymes “unzip” the DNA molecule by breaking the bonds of the base pairs, then synthesize a complimentary strand of DNA for each of the original strands.

30. DNA Replication

31. The Structure of RNA • RNA, like DNA, consists of a long chain of nucleotides, each made up of a sugar, phosphate group, and a nitrogenous base. • RNA differs from DNA in three main ways: • The sugar is ribose. • RNA is single stranded. • RNA contains Uracil (U) in place of Thymine.

32. Function of RNA in Cells • The primary function of RNA in cells is protein synthesis. • The assembly of amino acids into proteins is controlled by RNA. • The three main types of RNA are: • mRNA (messenger) • rRNA (ribosomal) • tRNA (transfer)

33. Protein Synthesis • RNA is produced within a cell from a strand of DNA through a process called transcription. • mRNA is transcribed in the nucleus, enters the cytoplasm, and attaches to a ribosome. • Next, translation of the mRNA strand occurs with assistance from tRNA within the ribosome, synthesizing proteins from amino acids.

34. Protein Synthesis • Proteins are made by joining amino acids into long chains called polypeptides. • Each polypeptide consists of a combination of any or all of the 20 different amino acids. • The properties of these proteins are determined by the order in which the amino acids are joined to form the polypeptides.

35. The Genetic Code • The “language” of mRNA instructions is called the genetic code. • This code is written in a language that has only four letters, AUCG. • The code is read three letters at a time so that each word of the coded message is three bases long. • Each three letter word is known as a codon.

36. The Genetic Code • A codon consists of three consecutive nucleotides that specify a single amino acid that is to be added to the polypeptide. • There are 64 possible three-base codons. • Some amino acids can be specified by more than one codon.

38. Amino Acids

39. The Roles of RNA and DNA • DNA acts as the “master plan” and is stored safely within the nucleus of the cells of an organism. • DNA controls every action of a cell and essentially every characteristic of an organism by producing “blueprints” in the form of RNA which will translate into proteins that control cellular functions and characteristics.

40. Genetic Mutations • Mutations are changes in the DNA sequence that affect genetic information. • Gene mutations result from changes in a single gene. • Chromosomal mutations involve changes in whole chromosomes. • Mutations can be beneficial to an organism, deleterious to an organism, or have no effect at all.

41. Gene Mutations • Mutations that affect one nucleotide are called point mutations. • Some point mutations substitute one nucleotide for another, resulting in a change in the translated amino acid in a protein.

42. Gene Mutations • If a nucleotide is inserted or deleted, a frameshift mutation can occur. • Frameshift mutations typically result in big changes in the translated amino acids of the protein, often altering the protein so it is unable to perform its normal functions.

43. Chromosomal Mutations • Chromosomal mutations involve changes in the number or structure of chromosomes. • These mutations can result in the deletion of genes from chromosomes, the inversion of genetic code, translocation, and duplication of genes on chromosomes.

44. Human Traits • A pedigree is a diagram used to show how a particular genetic trait is passed down from generation to generation – a genetic family tree. • Squares represent males and circles represent females. A horizontal line connecting a square and circle illustrates a parental generation. Siblings are always drawn with the oldest to the left, youngest to the right.

45. Pedigrees • Pedigrees can illustrate carriers of a genetic trait, as well as those exhibiting the effects of the trait. • Fully shaded squares/circles represent individuals who exhibit the trait. (Homozygous dom./rec.) • Half shaded squares/circles represent individuals who carry the trait but who do not exhibit the effects of the trait. (Heterozygous)

46. Pedigree of the Royal Family

47. Human Heredity • A karyotype is a micrograph of the pairs of homologous chromosomes, taken during mitosis. • Human cells each contain 22 pairs of autosomes and one pair of sex chromosomes equaling a total of 23 pairs (or 46) total chromosomes. • Females have identical sex chromosomes (XX) while males have two different sex chromosomes (XY).

48. Autosomal Recessive Disorders

49. Autosomal Dominant Disorders

50. Sex-linked Genes • Many genes are found on the X and Y chromosomes and are therefore referred to as sex-linked genes. • More than 100 sex-linked disorders have been mapped on the X chromosome. • Sex-linked disorders include: • Colorblindness • Hemophilia • Duchenne Muscular Dystrophy