Meiosis. ~ fragmentation - pieces split off and each piece becomes a new organism - starfish

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1 ** We are starting with section 3 because in order to understand Genetics, we must first understand how the cells and chromosomes divide to form the gametes! Meiosis 5 3 Just know the ones that are highlighted! There are many types of reproduction... ~ binary fission - done by bacteria ~ asexual - just split in half - amoebas ~ fragmentation - pieces split off and each piece becomes a new organism - starfish ~ budding - whole organism grows off another and then splits off - hydra ~ parthenogenesis - female makes a viable egg that grows without being fertilized - water fleas ~ sexual - 2 parents give genetic material to make offspring that are genetically different from them - most eukaryotes * advantage - genetic diversity! Nov 10 11:15 AM 1

2 * Remember that homologous chromosomes are chrom. of the same type ex: chrom. 1 from mom is homologous to chrom. 1 from dad Germ cells give rise to gametes - sex cells...sperm and eggs! * when gametes from the parents combine, the result is called a zygote gametes = haploid = 1 of each type of chromosome (1n) zygote = diploid = 2 of each type of chromosome (2n) so for humans, in each gamete the 1n = 23 in each diploid cell the 2n = 46 Nov 10 11:27 AM 2

3 We have already looked at making more body cells through mitosis... Let's look at how to make the gametes through Meiosis! ** Meiosis is cell division that makes daughter cells with half the number of chromosomes than the parent cell. 2 divisions take place: Meiosis I - first division Meiosis II - 2nd division Nov 10 11:35 AM 3

4 Meiosis I - first division ~ Prophase I - chrom. condense - nuclear envelope breaks down - homologous chrom. pair up - crossing over can occur Nov 10 11:43 AM 4

5 ~ Metaphase I - spindle fibers move homologous chrom. to middle of cell - homologues remain together Nov 10 11:47 AM 5

6 ~ Anaphase I - homologous chrom. move to opposite poles Note! Chromosomes DO NOT separate at the centromere at this stage!! Nov 10 11:47 AM 6

7 ~ Telophase I - chrom. gather at poles - cytoplasm starts to divide ~Cytokinesis - cytoplasm divides Nov 10 11:49 AM 7

8 Now we have 2 cells with 1/2 the # of chromosomes... BUT we still have 2 chromatids on each chromosome!! We now need to split these up! Meiosis II ~ Prophase II - new spindles form Nov 10 12:06 PM 8

9 ~ Metaphase II - chrom. line up in middle Nov 10 12:12 PM 9

10 ~ Anaphase II - chrom. divide at centromeres and chrom. move to either pole Nov 10 12:14 PM 10

11 ~ Telophase II - nuclear envelope forms around each set of chrom. - spindles disappear - cell begins to divide ~ Cytokinesis - cell divides This results in a total of 4 new haploid cells that are genetically different from the parent cell! FYI: When this process occurs, the homologous chromosomes will be randomly distributed ~ called independent assortment (we'll talk more about this later!) Also, the fertilization of gametes is random as well! ~ there are about 64 trillion combinations of chromosomes!! Nov 10 12:20 PM 11

12 Mendel and His Peas! 5 1 Genetics study of heredity * Research done by Gregor Mendel ( ) began research by studying pea plants and noting traits that were passed down through generations he went further by counting the # of plants with certain traits in each generation led to today's way of research Nov 10 1:44 PM 12

13 Why peas? 1.) Many varieties exist easy to tell the difference between them 2.) One of the 2 forms of each character would disappear in a generation and then reappear in the next easy to count this 3.) Fast growing and produces many offspring 4.) Easy to cross pollinate *Note* peas are self-pollinaters they don't need another flower to reproduce Mendel removed the male parts of one flower (stamen) and removed the female parts from another (pistil). He used the opposite to fertilize the other flower. Cross-pollination Nov 10 2:42 PM 13

14 Mendel's experimental design: 3 steps 1.) Allowed each pea plant to self pollinate for several generations this ensured true-breeding offspring only displays one form of a trait ex: all flowers are white and only make other white flowers when bred * P generation = parent generation Nov 10 2:52 PM 14

15 2.) Cross pollinated 2 P gen. that had contrasting traits Ex: purple flowers with white flowers * F1 generation = first filial gen. Noticed all flowers of the F1 gen. were purple! Nov 10 2:56 PM 15

16 Ch. 5 Meiosis and Genetics.notebook 3.) Allowed F1 gen. to self pollinate one time *F2 generation = second filial gen. *These are the plants that he counted! Observed a 3:1 ratio in F2 gen. every time! Dominant traits trait that remains seen (expressed) in F1 gen. Recessive traits trait that is not seen (not expressed) in F1 gen. *Noticed that the recessive plants were true breeding when allowed to self pollinate. *Also noticed that the dominant plants were producing 3:1 ratio when they self pollinated! **This meant the 3:1 ratio in F2 was really 1:2:1! 1 plant = dominant, true breeding 2 plants = not true breeding 1 plant = recessive, true breeding Nov 10 3:02 PM 16

17 Traits and Inheritance 5 2 For each trait, you get one gene from Mom, one from Dad *each gene may not have the same info! Same info = homozygous EX: has two purple genes or two white genes Different info = heterozygous EX: has one purple gene and one white gene *Each copy of a gene is called an allele Nov 15 11:46 AM 17

18 Genotype the set of alleles that an individual has EX: if we have a true breeding purple flowering plant, then it must have two dominant alleles = homozygous dominant is then its genotype! Phenotype how a trait looks when expressed determined by alleles that code for that trait Nov 15 11:51 AM 18

19 Probability and Punnett squares! When we look at the alleles, we use symbols to represent the traits *CAPITAL LETTERS = DOMINANT *lower case letters = recessive **Must use the same letter to represent the two forms of one gene! Ex: For height, you might use T for the dominant tall and t for recessive short. ~ Each trait has 2 alleles so you must write the letter for each allele! Ex: homozygous dominant = TT homozygous recessive = tt heterozygous = Tt *ALWAYS write dominant first for each trait! Nov 15 12:24 PM 19

20 Probability: the likelihood that a certain event will occur Can determine probability like this Probability = # one kind of possible outcome total # of all possible outcomes Q: If there are 20 pea plants being tested for height, and 15 of them had the dominant tall height; 5 had the recessive short height what is the probability of being a short pea plant? A: P = 5/20 1/4 So, there is a 1 in 4 chance the plant will be short! Nov 22 9:34 AM 20

21 Monohybrid crosses: cross that provides data about one pair of contrasting traits EX: *both parents are homozygous for their trait you could write... one is TT one is tt * can also both be heterozygous for their trait you could write... *both are Tt * or can be mixed you could write... one is TT one is Tt Nov 22 9:41 AM 21

22 Can use a Punnett square to predict the probable outcome of a cross! The ratios are very different from each other depending on what you are crossing Ex: TT x tt We can also figure out the ratios (or probablities) by counting the phenotypes and genotypes! Phenotypic ratio: Genotypic ratio: Nov 22 9:48 AM 22

23 Let's cross these! Tt x Tt Phenotypic ratio: Genotypic ratio: Nov 22 12:16 PM 23

24 Let's try this combo! TT x Tt Phenotypic ratio: Genotypic ratio: If you want to get a bit more difficult, I can show you a dihybrid cross! Just for fun and extension...watch this! Nov 22 12:15 PM 24

25 More about Traits! Incomplete dominance: both traits are shown as a mix or blend of the two traits * neither allele is dominant Ex: a white flower x a red flower = pink flowers in F1 gen. Nov 22 12:25 PM 25

26 Ch. 5 Meiosis and Genetics.notebook Codominance: two dominant alleles are expressed at the same time Ex: homozygous red horse x homozygous white horse = a roan horse both red and white hairs are found on the horse's coat Red Roan Blue Roan Nov 30 9:36 AM 26

27 Ch. 5 Meiosis and Genetics.notebook Multiple Alleles: traits that have genes with more than 2 alleles Ex: blood types A B o A and B are dominant o is recessive A and B are codominant to form the AB blood type So can have 4 different blood types with many combinations AA, Ao BB, Bo AB oo **Note with mult. alleles, you may see them written like this: IAi or IAIB Let's do a punnett square to see how blood types are passed down: Nov 30 9:41 AM 27

28 Polygenic traits: *traits controlled by more than one gene are polygenic ex: skin color in humans dozens of genes ex: eye color at least 3 genes code for color ~ generally, brown is dominant to green which is dominant to blue **This is a basic explanation but there are actually more genes that give us the vast array of eye color! *All polygenic traits are complex! ** if you would like to research more, please do so for extra credit! Nov 30 10:41 AM 28

29 Environmental factors: *some genes are triggered to work in different conditions Ex: arctic foxes and hares: white fur in winter, brown fur in summer ~the temperature triggers genes to be turned on or off which changes the fur color! Nov 30 11:16 AM 29

30 Pedigrees! Tracking traits in families: can determine your pedigree (family history) by noting the traits your family members show or have! Here's how a pedigree works: circles are female squares are male shaded in means they express the trait not shaded means they do not express the trait half shaded means they are a carrier of the trait ~horizontal lines connecting male and female indicates marriage ~vertical lines or brackets indicate their children ~ Let's look at a basic dom/rec. trait...tune deafness! Lets look at a sex linked trait... Nov 30 12:00 PM 30