Biological basis of life and Mendel

Transcription

1 Biological basis of life and Mendel 1

2 Issues with Darwin's Evolutionary Theory??? 2

3 Key terms and definitions Amino acids - molecules that are the basic building blocks of proteins Chromosome - structures made up of compacted DNA and protein visible during cell replication Codon - (also referred to as a triplet) a set of three bases coding for a specific amino acid Nucleotide - the basic unit of DNA composed of a sugar, phosphate, and base Genome - complete genetic makeup of an individual or species 3

4 Cells - fundamental units of life in all biological organisms Eukaryotic cells - composed of proteins, lipids, nucleic acids, and carbohydrates Proteins - molecules (structures with 2 atoms) serving different functions due to their binding to other molecules. Protein synthesis - DNA-directed manufacturing chains of amino acids to function into protein molecules 4

5 Cells - General Composition Organelles - substructures in the cell performing various functions E.g., protein synthesis, energy storage, waste disposal, etc. Nucleus - contains DNA and RNA Ribosomes - organelles in part made up of RNA; involved in protein synthesis Mitochondria - powerhouse of the cell - produces energy; think: cell's engines; also has DNA: mtdna 5

6 Cells - Two types Somatic cells - body tissues e.g., organs, brain, bone, and muscle Sex cells (gametes) - unites with another gamete from each parent which forms a zygote. They transmit genetic information from parents to offspring. Zygote - Potential to develop into a new organism, contains all the chromosomes (46 for us) 6

7 Proteins Function - attach to various molecules to perform different functions Hemoglobin (Hb) - binds w/ oxygen and transports it around the body Collagen - (tissue composition) - most common protein in the body Enzymes - regulate chemical reactions; E.g., digestive enzyme lactase breaks down lactose into simpler sugars. Hormones - affect different tissues and organs. E.g., Insulin made by specialized pancreas cells causes the absorption of glucose in liver cells 7

8 DNA DNA (deoxyribonucleic acid) - Double-stranded host of the genetic code RNA (ribonucleic acid) - single-stranded molecule messenger (mrna) transfer (trna) DNA + RNA contain the genetic information controlling the cell's functions 8

9 DNA Structure -nucleotides stacked on top of each other form the double-stranded twisted ladder-like structure Nucleotides: composed of a sugar, a phosphate (sides), and a nitrogenous base (rungs) Bases - form complementary bonds Adenine bonds with Thymine and Guanine bonds with Cytosine 9

10 Protein Synthesis DNA determines the structure and function of proteins Proteins: made of chains of amino acids Function is determined by the number and arrangement of amino acids making up the chain Amino acids - building blocks of proteins 10

11 Protein Synthesis - Two stages 1. Transcription (in the nucleus) -complementary strand of mrna produced from DNA strand -m(essenger)rna has Uracil instead of Thymine 2. Translation (in the ribosomes) -ribosomes 'read' mrna three bases at a time (codons) -t(ransfer)rna binds with matching codons creating amino acid chain 11

12 DNA Replication Growth and healing/repairing tissue is possible because cells are able to multiply and make exact copies of themselves. The new copies (daughter cells) have their own DNA, which is also replicated Process of DNA replication 1. Enzymes 'unzip' bonds between the bases 2. Separated nucleotide chains act as templates for the formation of a new nucleotide strand 3. Unattached nucleotides pair with complementary bases 12

13 Chromosomes After DNA replication, DNA becomes tightly coiled to form chromosomes Chromosomes Structure - single-stranded during normal cell functioning and double-stranded during cell division Types of chromosomes Autosomes - govern all physical characteristics minus sex determination Sex chromosomes - X and Y XX - mammal females XY - mammal males 13

14 Chromosomes Humans have 46 chromosomes, whereas gorillas and chimpanzees have 48. Karyotype - Chromosomes are visible during cell division 14

15 Mitosis - cell division for somatic cells -occurs during growth and repair of tissue Phase 1: DNA replication - 46 single-stranded chromosomes become 46 double-stranded chromosomes. Phase 2: Cell division - 46 double-stranded chromosomes are split and make up the genetic material in two daughter cells. -Daughter cells are identical - 46 single-stranded Note: clone - organisms that are genetically identical to each other 15

16 Meiosis - specialized cells found in the ovaries and testes -two cell divisions resulting in four daughter cells which each carry half the original number of chromosomes Recombination -genetic material is exchanged between partner chromosomes -daughter cells are no longer identical to their parents or each other -variation is introduced into reproducing populations of organisms 16

17 Cell Division - Complications in meiosis and Sex Chromosomes Complications with meiosis 98% of newborns have correct numbers of chromosomes 50% of pregnancies end in miscarriages. 70% of those miscarriages result from abnormal chromosome numbers. -nondisjunction - homologous chromosomes [strands] fail to separate during meiosis - results: monosomy or trisomy E.g., Down syndrome (trisomy 21) occurs when chromosome 21 is copied three times in an individual, a phenomenon occurring 1/1000 births. 17

18 Mitosis and Meiosis - types of cell division Recap Mitosis -Somatic cells (i.e., body cells - skin, hair, muscle, etc.) are duplicated -ONE division produces cells with all 46 chromosomes Results: two daughter cells, genetically identical to parents and siblings Meiosis -Gametes (sex cells like sperm and ova in humans) -TWO divisions produces cells with only 23 chromosomes Results: four daughter cells, not genetically identical 18

19 Unlike mitosis, meiosis involves... -Gametes transmit genetic info from parent to offspring Crossing over: chromosomes break and reconnect onto different chromosomes which results in... Recombination: new combinations of genetic information is created -Every generation has new genetic combinations = additional variation 19

20 Mutations Any change in DNA e.g., point mutations - (DNA bases-changes), changes in chromosome number or structure,... Potential effects -stop the creation of a protein -result in the creation of a defective protein, ultimately corrupting the function of a cell. -important evolutionary consequences if inherited 20

21 NEW genetic information? Recombination generates new combinations of genetic information But Mutations - changes in the nucleotide sequence of DNA -Only way NEW genetic variation is introduced 21

22 Genes - structures and functions "a sequence of DNA bases that specifies the order of amino acids in an entire protein, a portion of a protein, or any functional product [like RNA]" (58p) Structure Composition: 100s-1000s of nucleotide bases Organization: coding and noncoding segments Function Regulatory genes - to switch on/off other DNA segments. E.g., Hox genes - direct body plan development and embryonic tissue segmentation. 22

23 Take home quiz How it works -Friday, June 30 at 5pm the quiz will be ed and available on the course website DUE DATE: Sunday, July 2 at midnight -students must their answers (in the body or as an attachment) before the date above Format 20 questions total - 15 multiple choice and 5 short answer (must answer all five) Content Chapters 3 and 4 23

24 Mitosis and Meiosis - types of cell division Recap Mitosis -Somatic cells (i.e., body cells - skin, hair, muscle, etc.) are duplicated -ONE division produces cells with all 46 chromosomes Results: two daughter cells, genetically identical to parents and siblings Meiosis -Gametes (sex cells like sperm and ova in humans) -TWO divisions produces cells with only 23 chromosomes Results: four daughter cells, not genetically identical 24

25 Natural selection and genetics Natural selection - Traits making reproductive success more likely given environmental pressures will appear in higher frequencies from generation to generation. Sources of Variation *Mutations - new genetic information *Meiosis (recombination) - new combinations of genetic information Result: new variation in every generation of sexually reproducing populations Now we know how the variation NS needs to act on is created. (Thanks science!) 25

26 Mendel s Monk experimenting with peas Recall: Cross-breeding - artificial selection, farmers...metaphor for natural selection Missing in Darwin's theory of NS: a mechanism governing how traits were inherited Background -Mendel cross-bred pea plants -Observed the traits individual plants possessed over thousands of generations Inferred the Principles of Inheritance 26

27 Mendel - Cross-breeding pea plants Mendel inferred: regularity governed by a mechanism of inheritance; specifically, *Inheritance is determined by a 'unit' (gene) offspring receive from their parents *Individuals inherit one 'unit' from each parent for each trait *Traits might not be expressed in an individual but can still be passed on to the next generation 27

28 Mendel - overview -Cross-bred pea plants for thousands of generations -different trait expressions controlled by discrete units (genes) alleles - the different expressions of a gene The principles of inheritance 1. Segregation - for a trait, the pair of alleles from each parent separate and only one passes from parent to offspring. Meiosis - NOW we know this principle is Meiosis 2. Independent Assortment - different pairs of alleles are inherited by offspring independent from one another. 28

29 Mendel - inferences from observations Note: Parent plants = purebred = homozygous for pod color I.e., each parent has identical expressions of the 'unit' (gene) for this trait E.g., trait: seed color; expression: yellow or green. Y = yellow allele and G = green allele. Parent 1 = YY (this is the allele pair) Parent 2 = GG 29

30 Mendel's Inferences Genotype - genetic makeup of an individual (e.g., YY, GG, YG, etc) Phenotype - physical expression of an individual's genotype (e.g., yellow, green, tall, short, smooth, wrinkled, etc.) Mendel observed: Some allele expressions dominate others. E.g., Pea pod genotype = YG resulted in phenotype yellow so the dominant expression/form/allele = yellow (green is recessive) E.g., Trait: height; alleles: tall T, short t 30

31 Dominance and recessiveness Recessive - traits that are not expressed in heterozygotes Dominance - traits that are expressed in heterozygotes AND homozygotes -prevent the expression of recessive alleles in heterozygotes. Alleles - the different expressions of a gene Genes - segments of DNA -direct protein synthesis -found at different locus or loci of a chromosome E.g., H = tall = dominant allele and h = short = recessive allele 31

32 Mendelian traits Mendelian traits - discrete traits determined by alleles at a single genetic locus Dominant: cleft chin, dwarfism,... Recessive: Phenylketonuria (PKU), albinism, sickle-cell anemia -Recessive disorders manifest if homozygous - if heterozygous, a person = unaffected but carrier 32

33 Polygenic Traits Polygenic - traits influenced by genes at 2 or more loci E.g., skin, eye, and hair color Continuous traits - gradation of difference in several expressions 33

34 Mendelian vs Polygenic Mendelian: discrete categories of variation Polygenic: continuous Both -determined by Mendelian principles at specific loci -Dominance and recessiveness still a factor NOTE: Mendelian traits = less likely affected by environmental factors 34

35 Modern Evolutionary Theory Modern synthesis in the later 1920s-early 30s. Evolution now defined in two stages 1. Variation - inherited differences among organisms is produced and redistributed through various processes 2. Natural selection acts on variation resulting in differential reproductive success (85p). Current definition of Evolution: Change in allele frequency from one generation to the next. Allele frequencies: indicators of a group/population's genetic composition -Described as proportions or percentages of a total 35

36 Modern Evolutionary Theory Factors that produce and redistribute variation 1. Mutation - any change in DNA -"the only way to produce new genes (that is, variation)" (86p). 2. Recombination - exchange of DNA segments b/w chrom. pairs during meiosis 3. Gene flow - Migration and Nonrandom mating - movement of alleles w/in and between popns 4. Genetic Drift - Founder effect and Bottlenecking - change due to change to due small population = reduced genetic diversity 36

37 Modern Evolutionary Theory Factors that produce and redistribute variation 1. Mutation - any change in DNA -"the only way to produce new genes (that is, variation)" (86p). 2. Recombination - exchange of DNA segments b/w chrom. pairs during meiosis 3. Gene flow - Migration and Nonrandom mating - movement of alleles w/in and between popns 4. Genetic Drift - evolutionary change due to small population size -evolutionary change due to random factors Founder effect - smaller population of founders leaves parent group to form a colony elsewhere -reduction of genetic variation 37

38 Modern Evolutionary Theory 5. Natural selection - acts on the variation produced and distributed by 1-4 -Directs change in the allele frequencies of a population relative to environmental factors Microevolution - small genetic changes that occur w/in a species Macroevolution - large-scale changes that occur in populations over many generations -result in speciation 38

39 Current theory of natural selection Natural selection provides directional change in allele frequencies relative to specific environmental factors If the environment changes, then selective pressures change too If there's long-term directional change, then allele frequencies will shift gradually each generation 39

40 Ch 5 Macroevolution 40

41 Taxonomy and Species Concepts Biological Species Concept (BSC) - isolated populations gradually change over time and become distinct taxonomic groups -Taxonomic grouping heavily influenced by genetic drift and natural selection Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Primates Family: Hominidae Genus: Homo Species: sapiens We are Homo sapiens (also H. sapiens for short). 41

42 Macroevolution aka speciation Macroevolution - synonymous with speciation Focus: large-scale evolutionary processes Synthesize our understanding of modes of evolutionary change, geologic time, and taxonomic classification 42

43 Homologies Homologies - Structures shared by species due to common descent E.g., Humans, birds, and bats: same basic bone structure but modified 43

44 Analogies Analogies - similar structures arise in other lineages in response to different functional demands 44

45 Classification schemes: Systematics and Cladistics Evolutionary Systematics: -use homologous traits to trace evolutionary relationships over time -focus: identify common ancestry between groups Cladistics: -uses homologous traits to separate organisms into taxonomic groups 45

46 Classification schemes: Systematics and Cladistics Similar: Both use homologies to trace evolutionary relationships Differ: Systematics uses homologies to trace common ancestry over time vs. Cladistics uses homologies to separate organisms into groups 46

47 Cladistics more explicit and rigorous Ancestral traits - similarities shared by many distantly-related groups that are inherited from a remote ancestor E.g., Grasping hand in humans -Mice, bears, and lizards all have lungs -Remember the similar bone structures between whales, bats, and humans? Derived traits - reflect specific evolutionary lineages -modified traits from last common ancestor unique to a given group 47

48 Adaptive radiation and ecological niche Adaptive radiation - is the rapid expansion and diversification of new life forms into open ecological niches. Speciation results in as many variations as allowed by (1) its adaptive potential; and (2) adaptive opportunities E.g., reptilian egg evolution spawned an adaptive radiation event by opening new adaptive niches on land. 48