Chapter 13 and 14 Study Guide BIO-181 PDF

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A Personal study guide material to memorize and apply chapters 14 and 13 of BIO-181....

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(How will I use this? When will I use it? Why is it used?)

Chapter 13 – Meiosis  

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Heredity = inheritance Genetics: heredity and inherited variation o Variation: non-identical copies of genes basically o Genes: coded information on the form of heredity units o Gametes: sexual chromosomes o Somatic: all cells in the body o Locus: specific location along the length of a chromosome o Clone: group of genetically identical individuals  Are also in mitosis Fertilization o Karyotype: ordered display of chromosomes o Other 22 pairs of chromosomes are called autosomes,  the extra 23rd pair determines if it will be X or Y o Homologous: 2 identical chromosomes  Human females have (XX), males have (XY) o Diploid cells: somatic cells with 2 identical chromosomes in a single set TWO  (2n = 46) o Haploid cells: gametes containing a single set of chromosomes FOUR  (n = 23) o Alternation of generations: has both diploid and haploid stages that are multicellular; happen in plants in some species of algae Meiosis 1 is similar to mitosis o Prophase 1  Crossing over & synapsis  2 members of homologous pair associates loosely along their length  Synaptonemal complex: zipper-like formation that holds one homolog tightly to the other  Synapsis- the DNA breaks are closed up so that each broken end is joined to the corresponding segment of the non-sister chromatid  Crossing over creates recombinant chromosomes, which combines genes inherited from each parent o Metaphase 1  Independent assortment  Creates genetic variation Meiosis 2 o Prophase 2  Spindles form  Chromosomes, each still composed of 2 chromatics associated at the centromere, are moved by microtubules towards plate

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o Metaphase 2  Chromosomes are position like in metaphase 1  Crossing over in meiosis 1 causes the 2 sister chromatids of each chromosomes to be different  Kinetochores of sister chromatids are attached to microtubules at opposite poles  Non-identical sister chromatids sort independently from one another, this increasing the number of genetic types o Anaphase 2  Breakdown of proteins holding chromatids together  Chromatids separate towards opposite poles o Telophase 2/Cytokinesis  Nuclei forms  Meiotic division of one parent cell produces four daughter cells, each with a haploid set Random nature of fertilization o Adds to the genetic variation arising from meiosis o Any sperm can fuse with any egg o If n = 3, there are 2^3 = 8 possible combinations o For humans with n = 23, there are 2^23 or 8.4 million combinations

Chapter 14 – Mendel and Gene Idea    

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Character: heritable feature (example: flower color) Trait: each variant for a character (example: like purple or white colors for flowers) Ture-breeding: plants that produced offspring of the same variety when they selfpollinate o Mendel used this Hybridization: mating 2 contrasting true-breeding varieties o True breeding: P Generation  Example: (PP and pp) o Crossing 2 true breeding parents differing in 2 characters produces dihybrids in the F1 generation, heterozygous for both characters  Dihybrid cross, cross between 2 F1 dihybrids, can determine whether 2 characters are transmitted to offspring as a package or independently o Hybrid offspring of P generation: F1 generation  ALL interspecies  Produces monohybrids, heterozygous for one character  Cross between these are called monohybrid crosses  Example: (Pp and Pp) o When F1 self-pollinates or cross pollinates, with other F1s, it’s the F2 generation  Example: (PP, Pp, Pp, and pp)  Ratios:  Genotype: 1:2:1 (1 PP, 2 Pp, and 1 pp)  Phenotype: 3:1 (3 purple, 1 white) o Phenotypes: physical appearance o Genotype: genetic makeup  Use Testcross to determine unknown genotypes; breeding mystery individual with a homozygous recessive  If any offspring display recessive, the parent must be heterozygous o Homozygous: same 2 alleles o Heterozygous: 2 different alleles Mendel’s model o First concept:  Alternative versions of genes account for variations in inherited characters  Alternative versions are called alleles o Second concept  For each character, an organism inherits 2 alleles from each parent  He made this without knowing about chromosomes  2 alleles at a particular locus may be identical, as in the true breeding plants of the P generation o Third concept  If the 2 alleles at a locus differ, then one (the dominant allele) determines the phenotype, and the other (recessive allele) has no noticeable affect o Fourth concept  Aka the Law of Segregation

The 2 alleles for a heritable character segregate during gamete formation and end up in different gametes  Thus, an egg or sperm gets only one of the 2 alleles that are present  Corresponds to the distribution of homologous chromosomes to different gametes in meiosis o Using the dihybrid cross, Mendel made the Law of Independent Assortment  States that each pair of alleles segregates independently of each other pair of alleles during gamete formation  Only applies to genes on different, nonhomologous chromosomes or those far apart on the same chromosome  Genes located near each other on the same chromosome tend to be inherited together  If not, its genetically linked Probability Laws o Both laws reflect probability o Multiplication and Addition rules  Applies to monohybrid crosses  Multiplication rule: states that the probability that 2 or more independent events will occur together is the product of their individual probabilities  Addition rule: the probability that any 1 of the 2 or more exclusive events will occur is calculated by adding together their individual probabilities 

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Mendelian Genetics o Relationships between genotype and phenotype is rarely as simple as pea experiments o Many heritable characters are not determined but only one gene with two alleles o However, basic principles apply even more to the complex patterns o Inheritance of characters from single gene may deviate when  Alleles are not completely dominant or recessive  When a gene has more than 2 alleles  When a gene produces multiple phenotypes Degrees of dominance o Complete: occurs when phenotypes of heterozygote and dominant homozygote are identical  One masks the other o Incomplete: phenotype of F1 hybrids is somewhere between the phenotypes of the 2 parental varieties  Example: red flower and white flower creates pink flower o Codominance: 2 dominant alleles affect the phenotype in sperate, distinguishable ways  Most genes exist in populations in more than 2 allelic forms  Example: ABO blood group  Determines by 3 alleles for the enzyme (I & i) that attaches A or B carbohydrates to red blood cells (fig. 14.11 in textbook)

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 Type AB blood displays codominance since they’re both present Relation between dominance and phenotype o Dominance isn’t better or stronger  Example: Tay-Sachs disease is fatal; a dysfunctional enzyme causes an accumulation of lipids in the brain (yikes)  Organism level, it’s recessive. Biochemical level, the phenotype is dominant. Molecular level, alleles are codominant Pleiotropy o Multiple phenotypic affects going on o The impact of a single gene on more than one phenotype  One slip-up could fuck up a lot basically Epistasis o A gene at one locus alters the phenotypic expression of a gene at another Polygenic Inheritance o Quantitative characters are those that vary in the population along a continuum  Example of characters: skin color and height o Quantitative variation usually indicates a polygenetic inheritance, an additive effect of 2 or more genes on a single phenotype Nature and Nurture o Another departure of Mendelian genetics arises when the phenotype for a character depends on the environment and genotype o Phenotypic range is broadest for polygenic characters o Traits that depend on the multiple genes combined with the environmental factors are called multifactorial  Example: getting more sun makes skin darker, no sun makes skin lighter  Exposure to the environment as a fetus can also affect genes  Example: Fetal Alcohol Syndrome (FAS)

Misconceptions o Dominant allele is said to be dominant only because it is what we see in an individual with a heterozygous genotype  Masks recessive allele, doesn’t subdue it  Doesn’t mean it’s more common, better, or stronger  Alleles are simply variations in the nucleotide sequence Recessively inherited disorders o Disorders are more recessive and range from relatively mild to life-threatening o An example would be Albinism  A result from enzymes that deposit melanin is knocked out  Needs 2 copies of dysfunctional allele  Also a monohybrid cross  1:2:1 genotype o Behavior

They only show up in individuals homozygous for the allele Carriers are heterozygous individuals who carry the recessive allele but are phenotypically normal; most individuals with recessive disorders are born to carrier parents  If recessive allele is rare, chance of meeting is low  Consanguineous mating (incest) increases the chance o Another example: Cystic fibrosis  Most common lethal disease in US, most of European descent  Results in defective or absent chloride transport channels in plasma membranes leading to a buildup of chloride ions outside the cell  Symptoms include thick mucus buildup in internal organs and abnormal absorption of nutrients in small intestine  1:2:1 genotype o ANOTHER example: Sickle-Cell (fig. 14.17 in textbook)  Mostly black folk in Africa and African Americans (actual Africans)  Caused by the substitution of a single amino acid in the hemoglobin protein in red blood cell  In homozygous individuals, all hemoglobin is abnormal  Symptoms include physical weakness, pain, organ damage, paralysis  Heterozygous are usually healthy but suffer some symptoms  1/10 have the trait  Heterozygotes are less susceptible to the malaria parasite, so there is an advantage to being one in regions where it’s common  Called heterozygous advantage and can be considered a evolutionary tradeoff Dominantly inherited disorders o Some human disorders are caused by the dominant alleles o Dominant alleles that cause a lethal disease are rare and rise by mutation o Achondroplasia- form of dwarfism caused by rare dominant allele  Dd and dd alleles (there’s only one possibility for the eggs but not the sperm)  Usually better in respect to the other types of dwarfism o Huntington’s disease  Degenerative disease of the nervous system  No obvious phenotypic effects until about 35 to 40 years of age  Once the deterioration begins, it doesn’t end  Hh- Huntington’s, hh-normal  All eggs carry the normal allele  (So what I’m getting is that men really do cause MULTIPLE problems lol.) o Pedigree Analysis  Pedigree: family tree that describes the interrelationships of parents and children across generations  Inheritance patterns can be described using this and used to make predictions of future offspring  

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Autosomal dominant: allele in which every generation you see a child with the phenotype, there is always at least one parent with it as well Autosomal recessive: allele that is possible to see a child having a phenotype while neither parent has it...