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Standard 4

Standard 4. Genetics. Genetics = The scientific study of heredity how particular qualities or traits are transmitted from parents to offspring.

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Standard 4

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  1. Standard 4

  2. Genetics • Genetics = The scientific study of heredity how particular qualities or traits are transmitted from parents to offspring. • Genetics is the science of heredity and variation in living organisms. Knowledge that desired characteristics were inherited has been implicitly used since prehistoric times for improving crop plants and animals through selective breeding. However, the modern science of genetics, which seeks to understand the mechanisms of inheritance, only began with the work of Gregor Mendel in the mid-1800s. An Introduction to Genetics and Heredity (00:52)

  3. Reproduction • Reproduction is necessary for genes to be passed on. • Reproduction is a characteristic for all living systems; being no individual organism lives forever, reproduction is essential to the continuation of every species. Some organisms reproduce asexually and other reproduce sexually. • Asexual reproduction = a type of reproduction where an organism replicates itself, by budding or dividing, without the involvement of other organisms. Mode of reproduction in which offspring arise from a single parent and inherit the genes of that parent only. Reproduction by cloning. • Sexual reproduction = production of new generations involving the exchange of chromosomes from both a male and female parent. Process in which two cells, termed gametes, come together to form one fertilized cell that contains genetic information from both parental cells.

  4. Reproduction • The three main ways that asexual reproduction can take place are by fission, fragmentation, and regeneration. • In fission or budding, one or more individuals are formed from an original. These new clones can either remain attached physically to the parent or break away from it. Stony corals commonly exhibit this type of reproduction. Gemmules, a type of internal budding, allow an organism to survive under drastic conditions. Sponges exhibit this type of reproduction • Fragmentation is another way to reproduce asexually. The parent breaks into different fragments, which eventually form new individuals. This process is exemplified by certain flatworms known as planarians. Asexual reproduction through budding.

  5. Asexual Reproduction • Advantages of Asexual Reproduction • well-adapted genotypes can be preserved and multiplied • root sprouts etc take advantage of already existing root system • no fragile seedling stage \ good for harsh environments • vigorous re-growth after disturbance • Asexual reproduction can be very advantageous to certain animals. For instance, animals that remain in one particular place and are unable to look for mates would need to reproduce asexually. Another advantage of asexual reproduction is that numerous offspring can be produced without "costing" the parent a great amount of energy or time. Environments that are stable and experience very little change are the best places for organisms that reproduce asexually. The cloned offspring are more likely to succeed in the same stable areas as their parents. • Disadvantages of Asexual Reproduction • little variation to cope with fluctuating environment (high adaptation, but low adaptability) • root sprouts-- disease spreads from old to young individuals of clone \ susceptible for fast spread of epidemics

  6. Sexual Reproduction • Advantages of sexual reproduction • Variety of progeny in the future • Seeds/fruits are formed- allows for effective long-distance dispersal • Disadvantages of sexual reproduction • Too much variation is a problem because it prevents close adaptation to any given environment • Seed germination and seedling stages are precarious due to high mortality rates in stressful environments Male Sperm Cell Attempting to Penetrate Female Egg

  7. GENETICS • Gregor Mendel ( 1822-1884) • Austrian monk • “Father of Genetics” • Experimented with pea plants • Used quantitative data analysis • Gregor Mendel traced the inheritance patterns of certain traits in pea plants and showed that they could be described mathematically. Although not all features show these patterns of Mendelian inheritance, his work suggested the utility of the application of statistics to the study of inheritance.

  8. GENETICS • Mendel observed that inheritance is fundamentally a discrete process with specific traits that are inherited in an independent manner. • These basic units of inheritance are now known as "genes". In the cells of organisms, genes exist physically in the structure of the molecule DNA and the information genes contain is used to create and control the components of cells. • Although genetics plays a large role in determining the appearance and behavior of organisms, it is the interaction of genetics with the environment an organism experiences that determines the ultimate outcome. For example, while genes play a role in determining a person's height, the nutrition and health that person experiences in childhood also have a large effect.

  9. GENETICS • Pea Plant Characteristics: • Round – Wrinkled Seed • Short – Tall • Green – Yellow Seed • Purple – White Flower

  10. GENETICS • Genetics = The study of heredity and how traits are passed on through generations. • Some traits aredominant • Dominant = An allele is said to be dominant if it expresses its phenotype even in the presence of a recessive allele. • Always represented with a capital letter: T = Tall • Some traits arerecessive • Recessive = A part of the gene that is only expressed if a dominant allele is not present • Always represented with a lower case letter: t = short T t

  11. GENETICS • Allele = a matched pair of genes for 1 characteristic • One allele is inherited from each parent • Tt = a pair of alleles for 1 characteristic – plant height • Rr = a pair of alleles for 1 characteristic – seed shape • Gg = a pair of alleles for 1 characteristic – seed color • Bb = a pair of alleles for 1 characteristic – flower color T t

  12. GENETICS • To figure out which traits will be present you need to set up a Punnett Square, invented by RC Punnett. • Can show 2 types of crosses – monohybrid or dihybrid crosses. • In a monohybrid cross, organisms differing in only one trait are crossed. (Tt x Tt) or (AA x aa) or (Ss x Ss) • A dihybrid cross involves a study of inheritance patterns for organisms differing in two traits. Mendel invented the dihybrid cross to determine if different traits of pea plants, such as flower color and seed shape, were inherited independently. (see limousine cattle) Gregor Mendel's Rules of Heredity: Using Punnett Squares (05:04) T t T t

  13. GENETICS • At its most fundamental level, inheritance in organisms occurs by means of discrete traits, called "genes". This property was first observed by Gregor Mendel, who studied the segregation of heritable traits in pea plants. In his experiments studying the trait for flower color, Mendel observed that the flowers of each pea plant were either purple or white — and never an intermediate between the two colors. These different, discrete versions of the same gene are called "alleles". Chromosomes and the Work of Gregor Mendel (06:06)

  14. Predicting the Resuts of a Cross Between a True Breeding Tall Plant and a True B (01:01) GENETICS • P1 Generation = the first parents crossed • F1 Generation = the first offspring • F2 Generation = a cross between 2 F1 parents T T t t

  15. GENETICS • Phenotype = The physical expression of the genotype; an organism’s physical & observable characteristics. Literally means "the form that is shown"; it is the outward, physical appearance of a particular trait. • Mendel's pea plants exhibited the following phenotypes: • - round or wrinkled seed phenotype • - yellow or green seed phenotype • - purple or white flower phenotype • - tall or dwarf/short plant phenotype • Genotype = The genetic make-up of an individual organism. (TtRr) • Purebred = an organism who, when mated with another purebred with the same characteristics, will always produce purebreds; genotypically, purebreds are homozygous. • Heterozygous= Having two different alleles of the same gene, one inherited from each parent. Tt, Rr, Aa, … • Homozygous= Having two identical alleles for a given trait, one inherited from each parent. TT, tt, RR, rr, AA, aa, …

  16. GENETICS • Breeding cattle: • P1 = Purebred red x purebred white R R r Rr Rr r Rr Rr Phenotype: 100% all red Genotype: 100% Rr

  17. GENETICS • Breeding cattle: • F1 = Rr x Rr Phenotype: 3:1 75% red 25% white R r R RR Rr r Rr rr Genotype: 1:2:1 25% RR 50% Rr 25% rr

  18. GENETICS • Incomplete Dominance = neither form of the gene is dominant • Shorthorn Cattle • R = Red • W = White • RW = Roan P1 cross: RR x WW R R W RW RW W RW RW Phenotype: 100% Roan Genotype: 100 % RW

  19. GENETICS • Incomplete Dominance = neither form of the gene is dominant • Shorthorn Cattle • R = Red • W = White • RW = Roan F1 Cross: RW x RW Phenotype: 1:2:1 1 red 2 roan 1 white R W R RR RW W RW WW Genotype: 1:2:1 1 RR 2 RW 1 WW

  20. GENETICS • Codominance • In codominance, neither phenotype is completely dominant. Instead, the heterozygous individual expresses both phenotypes. • A common example is the ABO blood group system. • The gene for blood types has three alleles: A, B, and i. • i causes O type and is recessive to both A and B. • The A and B alleles are co-dominant with each other. When a person has both A and B, they have type AB blood. A i

  21. GENETICS • Polygenic = A trait affected by many genes, no single gene has an over-riding influence. Any phenotype that results from the effect of multiple genes at two or more loci, with possible environmental influences too. Examples are: obesity, hypertension, hypercholesterolaemia, skin pigmentation, cancer, etc. • Some traits are determined by the combined effect of more than one pair of genes.  These are referred to as polygenic, or continuous, traits.  An example of this is human stature.  The combined size of all of the body parts from head to foot determines the height of an individual.  There is an additive effect.  The sizes of all of these body parts are, in turn, determined by numerous genes.  Human skin, hair, and eye color are also polygenic traits because they are influenced by more than one allele at different loci.  The result is the perception of continuous gradation in the expression of these traits. Polygenic traits:stature, body shape,hair and skin color

  22. GENETICS • Dihybrid Cross - Limousin Cattle - The history of Limousin cattle may very will be as old as the European continent itself. Cattle found in cave drawings estimated to be 20,000 years old in the Lascaux Cave near Montignac, France, have a striking resemblance to today's Limousin These golden-red cattle are native to the south central part of France in the regions of Limousin and Marche. The terrain of the homeland has been described as rugged and rolling with rocky soil and a harsh climate. Consequently, the growing of field crops was very difficult at best and emphasis was placed on animal agriculture. Limousin cattle, as a result of their environment, evolved into a breed of unusual sturdiness, health and adaptability. • Limousin cattle: B = Black b = red • Polled (without horns): P = Polled p = horns

  23. GENETICS • Limousin cattle: B = Black b = red • Polled (without horns): P = Polled p = horns • BbPp x BbPp • 4 possible gene combinations from each parent: BP Bp bP bp BP Bp bP bp BP BBPP BBPp BbPP BbPp Bp BBPp BBpp BbPp Bbpp bP BbPP BbPp bbPP bbPp bp BbPp Bbpp bbPp bbpp Phenotypic Ratio 9:3:3:1 Black Polled 9 Black Horned 3 Red Polled 3 Red Horned 1

  24. GENETICS • * Homework • Draw and label a homologous chromosome pair with heterozygous alleles highlighting a particular gene location.

  25. GENETICS • * Homework • #1 Cross a heterozygous black polled bull with a homozygous red horned cow: • BbPp x bbpp • #2 Cross a heterozygous black horned bull with a heterozygous black polled cow: • Bbpp x BbPp

  26. GENETICS • Males XY • Females XX • Sperm + Egg = Zygote = a 1 celled animal that grows by a process called MITOSIS

  27. GENETICS • Diploid = (2n) A full set of genetic material, consisting of paired chromosomes one chromosome from each parental set. Most animal cells except the gametes have a diploid set of chromosomes. The diploid human genome has 46 chromosomes. • Haploid = (1n) A single set of chromosomes (half the full set of genetic material) present in the egg and sperm cells of animals and in the egg and pollen cells of plants. Human beings have 23 chromosomes in their reproductive cells.

  28. GENETICS • PAIRS OF CHROMOSOMES IN LIVESTOCK & HUMANS: • Species# of Chromosomes Turkeys 41 Chickens 39 Horses 32 Cattle 30 Goats 30 Sheep 27 Humans 23 Swine 19

  29. GENETICS • Homo sapiens (human)46 • Mus musculus (house mouse)40 • Drosophila melanogaster (fruit fly)8 • Caenorhabditis elegans (microscopic roundworm)12 • Saccharomyces cerevisiae (budding yeast)32 • Arabidopsis thaliana (plant in the mustard family)10 • Xenopus laevis (South African clawed frog)36 • Canis familiaris (domestic dog)78 • Gallus gallus (chicken)78 • Zea mays (corn or maize)20 • Muntiacus reevesi (the Chinese muntjac, a deer)23 • Muntiacus muntjac (its Indian cousin)6 • Myrmecia pilosula (an ant)2 • Parascaris equorum var. univalens (parasitic roundworm)2 • Cambarus clarkii (a crayfish)200 • Equisetum arvense (field horsetail, a plant)216

  30. GENETICS • Mitosis = The process of dividing somatic cells (body cells) in which each daughter cell receives the same amount of DNA as the parent cell. • Purpose: Mitosis repairs body and allows for growth. • Mitosis has 6 steps: Interphase, Prophase, Metaphase, Anaphase, Telophase, and Cytokinesis. Mitosis (02:20)

  31. GENETICS • Interphase = “normal cell” • Cell grows • Most of the cell life is spent in this phase • Chromosomes double

  32. GENETICS • Prophase = chromosomes become visible • Nuclear envelope breaks down • Spindle fibers appear

  33. GENETICS • Metaphase = chromosomes line up at the equator • Spindle fibers attach to the centromere

  34. GENETICS • Anaphase = chromatids separate • Chromatids are pulled to opposite poles

  35. GENETICS • Telophase = chromosomes uncoil • Nuclear envelope reforms • Spindle fibers disappear

  36. GENETICS • Cytokinesis = cytoplasm divides • 2 new cells

  37. GENETICS • MITOSIS: • Body cells • 1 division • 2 cells produced • Cells are diploid (2n) • Allows growth and repair Mitosis (02:20)

  38. GENETICS • MEIOSIS: • Sex cells • 2 divisions • 4 cells produced • Cells are haploid (1n) • Allows for sexual reproduction

  39. Meiosis 2N 1N Meiosis in the male and female divides each diploid cell into 4 haploid sex cells.

  40. GENETICS • MEIOSIS: • Interphase 1 • Number of chromosomes doubles • Prophase 1 • Nuclear membrane breaks • Spindles appear • Chromosomes become visible • Homologous chromosomes line up next to each other = synapsis(AAaa) • Forms a tetrad = 4 homologous chromosomes • Crossing over = exchange of genes during Prophase 1, allows for genetic recombination

  41. GENETICS • MEIOSIS: • Metaphase 1 • Homologous chromosomes line up at the equator

  42. GENETICS • MEIOSIS: • Anaphase 1 • Homologous chromosomes separate and go to opposite poles

  43. GENETICS • MEIOSIS: • Telophase 1 • Nuclear membrane forms • Spindle fibers disappear • Chromosomes become less visible • Cytokinesis 1 • Pinches into 2 cells

  44. GENETICS • MEIOSIS: • Prophase 2 • Nuclear membrane breaks • Spindles appear • Chromosomes become visible

  45. GENETICS • MEIOSIS: • Metaphase 2 • Sister chromosomes line up in the middle

  46. GENETICS • MEIOSIS: • Anaphase 2 • Centromeres break and sister chromosomes separate to opposite poles

  47. GENETICS • MEIOSIS: • Telophase 2 • Nuclear membranes reform • Spindles disappear • Cytokinesis 2 • Splits to make 4 haploid (1n) cells Meiosis (02:33)

  48. Meiosis male female 2N 2N Diploid sex cell production sex cell production Haploid 2N 2N 2N 2N 1N 1N 1N 1N 1N 1N 1N 1N sperm egg Diploid Zygote 2N Fertilization

  49. GENETICS

  50. GENETICS

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