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GENETICS & INHERITANCE GENETICS = Scientific study of ______________ Gregor Mendel (1860) = ____________________________ Experimented with ______________ Used _______________(asexual reproduction) and cross-fertilization methods (sexual reproduction) chose simple traits to follow (flower color, height, seed color, seed texture etc.) Trait = any ___________that can be passed from parents to their offspring Gene = genetic material on a ___________that contains the instructions for creating a particular trait Allele = one of several _______of a gene, an alternate form of the same gene for a given trait example: A or a (same letter, different case) Locus = the __________on a chromosome where a gene is located Every ____________(body) cell contains two copies of each chromosome, one from each parent. This is called a _____________. Each chromosome in the pair contains a gene for the same trait at exactly the same loci. See PICTURE OF HOMOLOGOUS PAIRS HERE Monohybrid Cross = a cross involving only a _______ responsible for a trait; each parent contributes information for the trait (ex. Aa X AA) Dominant trait = the trait that gets expressed in a monohybrid cross where the mode of inheritance is ______________________; shown by a capital letter : A Recessive trait = the trait that is hidden in a monohybrid cross where the mode of inheritance is_________________; ______________shown by a lower case letter : a Homozygous = the two alleles for a trait that an organism has are ______________ex: Homozygous Dominant = AA , Homozygous Recessive = aa Heterozygous = the two alleles coding for a trait are __________________ex: Aa Genotype = the actual___________________, all the alleles that an organism possesses (the actual letters) Phenotype = ________________________based on alleles 1 GENETICS & INHERITANCE Mendel’s Laws of Heredity 1. Law of__________: When a trait is Completely Dominant over another trait, then that dominant allele controls the gene pair. In the heterozygous form (Aa) the dominant trait only gets expressed. The recessive allele gets hidden. 2. Law of___________: Pairs of alleles separate during the formation of the gametes (sex cells) during Meiosis I. Therefore each gamete will contain one allele for each gene. See picture of meiosis and fertilization here 3. Law of______________________: Gene pairs separate into the gametes both independently and randomly of each other. The rules of __________are used to describe how the different chromosomes and their alleles from parents assemble into ________and ultimately into__________. PUNNETT SQUARES Used to track a trait from parents to offspring. Shows possible ratios for offspring outcomes. P Generation = Parents F1 Generation = Offspring from the cross of the parents F2 Generation = Offspring produced from crosses among the F1 F = filial, refers to sons and daughters Rules: 1. Make a key; show dominant and recessive alleles 2. Properly label parents genotypes, place them on the outside of the punnett square 3. Correctly perform the cross 4. Interpret the results; determine ratios Monohybrid Cross ratios: Complete Dominance = 3:1 (Aa X Aa) ; 4:0 (AA X aa); 2:2 (Aa X aa) TEST CROSSES Suppose we have two Tall pea plants T= tall; t = short What are the possible genotypes for each plant? __________ or ___________ To find out whether an individual showing a dominant trait is homozygous or heterozygous, the individual can be crossed with an individual whose genotype is known for certain. What type of plant would we know for certain the genotype of? 2 GENETICS & INHERITANCE Test Cross: cross the tall plant (TT or Tt) with a short one (tt) If any recessive phenotypes show up in the next generation, the unknown genotype MUST be Heterozygous Homozygous tall x short Homozygous Tall x short TT x tt Tt x tt Offspring = Offspring = Chromosome Theory of Inheritance: genes that code for various traits are found on ____________which are made of _____ and found in the ____________of each cell Thomas Hunt Morgan (1910): Studies Drosophilia melanogaster ;common fruit fly Discovered the gene for eye color and wing size were both located on the same chromosome (X) = __________ Linkage = _____________________________________ The closer the genes are on the chromosome, the _____________the likelihood of crossing over The Law of _______________________does not apply to linked genes! Barbara McClintock & Harriet Creighton (1950): Studied Zea mays ; corn Looked at __________________ They noticed that 2 copies of it were different sizes Conclusion = ______________had occurred, an abnormal event caused a piece of another chromosome to attach itself to one of the copies of chromosome #9 Crossing Over disrupts_________________________! Chromosomes: Humans have __individual chromosomes in every cell of the body except the ___________ 22 pairs = _____________(regular, information carrying chromosomes) 1 pair = ____Chromosomes, determines gender (XX = female, XY = male) MODES OF INHERITENCE Different ways of inheriting genetic traits 1. Complete Dominance: dominant allele completely masks out the recessive trait (AA, Aa) Autosomal Dominant = trait carried on an autosome by a dominant gene (A) Autosomal recessive = trait carried by a recessive allele (aa) Example: flower color in pea plants P = Purple, p = white PP x pp 3 Pp x Pp GENETICS & INHERITANCE 2. Incomplete Dominance: One allele of a gene pair is not fully dominant over the other; being heterozygous produces an intermediate form, no masking occurs (AA, Aa, aa) Example: Flower color in snapdragons RR = red, rr = white, Rr = pink RR x rr Rr x Rr 3. Codominance: both alleles express themselves when heterozygous (Blood types A, AB, B, O). There is no true recessive trait. AB Blood type is an example of Codominance = Both alleles in the heterozygous form (IAIB ) end up expressing themselves equally. Both traits show up in the phenotype. Example: coat color in horses RR = red , WW = White , RW = roan (RR = red , R’R’ = White , R R’ = roan) RR x WW RW x RW 4. Polygenic Traits: trait is controlled by more than one pair of genes (Eye color, Skin color, Human Height). This usually results in continuous variation. Polygenic inheritance is considered the opposite of Pleiotropy. 5. Pleiotropy = when a single gene has more than one phenotypic expression. Example: Sickle Cell Anemia = misshapen red blood cells ultimately causes other problems such as anemia, pneumonia, heart & kidney failure, bone abnormalities, and impaired mental functioning. 6. Epistasis = one gene affects the phenotypic expression of a second gene. (Skin pigmentation) One gene codes for color, the other codes for the amount of pigment. 7. Multiple Alleles: a gene having more than two alleles (Blood types) PHENOTYPES * A B AB O % of Population 39% 12% 4% 45% GENOTYPES IAIA IBIB IAIB IiIi , IAIi , IBIi Discovered in 1900 by Dr. Karl Landsteiner Based on the presence or absence of specific agglutinogens (clotting factors) on the surface of red blood cells (RBC’s = Erythrocytes) 4 GENETICS & INHERITANCE For example: a person with blood type A posseses A-antigens and Anti-B antibodies The blood will clot if a foreign Antigen is present Universal Donor = Blood type O ; contains no A or B antigens No Clotting reaction Universal Recipient = Blood type AB ; contains both A & B antigens Will recognize antigens from any blood type Rh Factor = (Rhesus monkey) You either have it (+) or you don’t (-) Sensitization can occur by: 1.) Rh+ blood transfused into Rh- person 2.) Rh- mother carries a fetus who is Rh+ IAIA x IBIB IAIix IBIi 8. Sex-Linked Inheritance: trait carried on the sex chromosomes; usually the X (XX = female; XY = male) a X-Linked Recessive = X (Colorblindness, Hemophilia) X-Linked Dominant = X ; Y-Linked (Rare) Carrier = person not affected by the trait but can pass it on to offspring = A A a X X Only females can be carriers for sex-linked traits because if a male has the gene, he will also exhibit the trait! A A X X x Xa Y A a x X X XA Y 9. X – inactivation: one of the two X chromosomes in a female does not uncoil during embryonic development. The chromosome that remains coiled is called a Barr Body and contains genes that will not get expressed. This could cause a sex-linked trait to affect a female that would normally be only a carrier. 10. Sex-Influenced Traits: expressed in both sexes, but they are expressed differently (Pattern Baldness) B= Normal; b= Bald female (bb) = bald; male (bb or Bb) =bald BB x Bb Bb x Bb 11. Sex-Limited Traits: autosomal traits expressed in only one sex (Lion’s mane) 12. Dihybrid Crosses: follow 2 traits at a time (AaBb) Example: A = purple flowers, a = white B = Tall, b = short 5 GENETICS & INHERITANCE If you cross two parents, where the father is AABB and the mother is aabb: the possible gametes are AB x ab. This can be determined using the F.O.I.L method. F = first O = outside I = inside L = last Results = 100% AaBb Suppose we cross AaBb x AaBb: GENETIC DISORDERS Disorders or diseases related to a persons genes or chromosomes; inherited in the same ways as other traits. 2 Mechanisms exist: 1. Inherited on Genes: inherited as a trait (Autosomal, sex-linked, sex influenced, etc...) colorblindness hemophilia “bleeder’s disease” muscular dystrophy albinism Progeria 2. Chromosome Abnormalities: not caused by a gene A.) Extra or Missing Chromosomes. Aneuploidy = abnormal chromosome number Non-Disjunction = failure of chromosome pairs to separate properly during meiosis, end up with daughter cells having either too many or not enough chromosomes in them. Ex. Down Syndrome “Trisomy 21” B.) Mutated Chromosome = damaged DNA, genes located in that section are damaged Deletion: missing gene or piece of chromosome Duplication: extra piece, genes duplicated Translocation: gene switches chromosomes Inversion: fragment of gene gets turned around SCREENING FOR DISORDERS 1. Karyotyping = genetic map of all the chromosomes that an organism possesses 2. Amniocentesis = test done before birth, take sample of amniotic fluid (C.V.S.) 3. Genetic Counseling = determine family medical history 6