Genetics: Exploring The World of DNA, Chromosomes, and Inheritance

SBI3U Grade 11 Biology Genetics Test Genetics DNA: Molecule found in Nucleus: Deoxyribonucleic Acid Structure: Double Helix, Twisted Ladder, Coiled in Chromosomes Function: To contain all of the instructions for life DNA inside chromosomes, inside the nuclei of the cell Structure: Deoxyribose: Sugar molecule Phosphate: w/ sugar makes backbone of ladder Nitrogenous Base: Adenine, Thymine, Cytosine, Guanine -Adenine + Thymine are purine: 2 rings –Guanine and Cytosine are pyrimidines: 1 ring Nucleotide: Phosphate + Deoxyribose + Nitrogenous base pair Base Pairs: Pairs of nitrogenous bases, always pairs AT and CG Gene: segment of DNA that encodes instructions for Protein RNA retrieves instructions from DNA and takes it out to make protein DNA twists on itself -> twists with Histone (beads) -> histones twist to make chromatid Chromosomes -Each human has 46 chromosomes -23 pairs in total -1 pair sex chromosomes (that define your sex, male XX, female XY) -22 pairs of autosomes (not sex chromosomes) -Each pair is homologous – same instructions but different messages -Not all living things have the same number of chromosomes Centromere: middle region of chromosome, attracts spindle fibers N: Haploid: # of unique chromosomes -> human is 23 2N: Diploid: # of total chromosomes Chromosome -> (before mitosis, copies in S phase) -> called “Sister Chromatids” when centromere is added Homologs: single chromosomes that are similar but not the same to another homolog Homologous Pairs: pairs of homologs after criss crossing that are ready for anaphase Cell Division Cell Division: Making new cells Mitosis: Occurs only in Somatic Cells -Daughter cell identical to parent cell Purpose: GROWTH, REPAIR, and REPLACE/REPRODUCTION Mitosis part of cell cycle Cell Cycle: 2 stages (Growth, and Division) growth being the longest Interphase: to increase volume and mass –G1: growth prepare to synthesize. Option to synthesize or rest phase –S (Synthesis) Phase: DNA duplication –G2 Phase: growth and prepare to divide. Chromosome made into 2 Sister chromatids held with centromere. Prophase: Chromatin condenses and becomes visible -Nuclear membrane breaks down -Begin to migrate to opposite poles, and held with spindle fibers Metaphase: Middle -Spindle Fibers attach chromosome and puts them on the equatorial plate -Sister chromatids face opposite poles Anaphase: Apart -Centromere splits -Sister chromatids pulled by spindle fibers Telophase: two -Nuclear membrane forms around each set of chromatids -Spindle fibers gone -Chromatids de condenses to chromatin. Chromatin = chromosome Cytokinesis: Occurs at the end. -cytoplasm divides into 2 through a pinching process -In plants, cell wall divides cell in half Meiosis: to make reproductive cells -Amount of chromosomes in daughter half as in mother -Difference between Mitosis: -2 prophase, anaphase, metaphase -Division happens twice -Crossing over of chromosomes -Results in genetically different cells Homologous: Similar cells but not the same, same genes, but with small differences. Haploid: Only one set of genes (1n) Diploid: pairs of genes (2n) -Divide such that the number of chromosomes is cut in half -Only occurs in gamete cells Meiosis 1 -Separates homologous chromosomes into 2 intermediate cells -Crossing over (shuffles chromosomes to create diversity) Interphase -Chromosomes replicate during interphase -Chromosomes not condensed during this stage -Sister chromatids are joined by centromere -Risk for gene mutation here creating alleles: creating 2 or more forms of a gene Prophase 1 -Chromosomes condense in prophase unlike in mitosis –Crossing over -Chromosome 1 will pair up with Chromosome 1 -Begin to tangle and cross over -Parts of the chromosome will be interchanged, and recombination occurs -happens 2-3 times per chromosome -referred to as Tetrads after crossing over Metaphase 1 –Spindle fibers hold them in the middle –Aligned randomly, face to face –Unlike Mitosis, Homologs split, instead of centromeres Anaphase 1 -Homologs separate and move to opposite poles of the cell -Centromeres do not split, so sister chromatids still held together and one chromosome will move to each pole of the cell Disjunction: normal separation of homologous chromosomes Nondisjunction: failure to disjoin during this phase, and 2 chromosomes go to each pole –Telophase 1 -Does not occur in all cells -Same as mitosis: Nuclear membrane reforms, de condenses chromosomes -Pinches in and separates 2 chromosome filled bodies. Cytokinesis 1 -Cytoplasm divided into 2 intermediate cells -Each one with a copy of chromosomes -Because each chromosome already has 2 sister chromatids, a second chromosome duplication does not take place between cytokinesis 1 and prophase 2 Meiosis 2 -Miotic Division: similar to mitosis -Purpose to divide and make haploid cells -Pulls apart the sister chromatids, dividing number of chromosomes for each gamete cell by 2 Prophase II -Consisting of duplicated sister chromatids, the chromosomes condense to become visible Metaphase II -Spindle fibers attract to the centromere and align them side by side along the equator in single file Anaphase II -Sister chromatids (now single stranded chromosomes) are pulled apart Telophase II -Nuclear membrane reforms -Each parent cell has 2 nuclei (human 23 chromosomes in each) Cytokinesis II -Parent cell divides into 2 resulting in haploid gamete cells or spores in plants Gametes: end result of meiosis Gametogenesis: production that creates sperm and egg Spermatogenesis: process of turning sperm gamete into sperm cell Oogenesis: process of making an egg from an egg gamete cell Spermatogenesis: –Takes place in testes of male –Spermatogonium: start of production cell -Haploid from meiosis goes through spermatogenesis and gets larger to make sperm -Results in a mature sperm with less cytoplasm and long flagellum –Spermatogenesis takes place throughout a man’s life and during mating seasons every year. Oogenesis -Takes place in ovaries of women –oogonium: start of egg cell -Unlike spermatogenesis, cytoplasm is NOT divided equally -Divided towards primary oocyte and other to Polar body -After Meiosis 2, only 1 cell survives, purpose is to give it enough nutrients and cytoplasm. -In humans, Meiosis 1 begins before birth in ovarian tissues, and eggs are frozen –Menopause: the pause of the frozen eggs prior birth till fertilization -Meiosis takes place AFTER fertilization -Releases 1 oogonium each month Karyotypes –Shows all the chromosomes in a cell arranged in a grid from Largest to smallest with centromeres lined up -Chromosomes are stained with Giemsa, a chemical that makes A and T bonds -Reveals the unique G-branding Preparation –Fetal Blood ß common -If inside fetus, they use Amniocentesis -Amniocentesis: insert a syringe in amniotic fluid to take floating skin cells. -Do centrifuge to have heavier cells sink and culture to do karyotype -Slow and takes days to culture –Chorionic Villi Sampling: Around placenta, chorionic villi grows and take some out to do karyotype -Faster only takes hours -Karyotypes only detects GROSS abnormalities, deletion, missing, or extra chromosomes –Polyploidy: extra chromosome –Aneuploidy: missing chromosome –Mixed: Translocation Karyotypes do not show DNA or individual genes, or small mutations Diseases Down Syndrome/ Trisome syndrome –Extra chromosome 21 -Intellectually disabled -Heart defects -Physical abnormalities Klinefelter Syndrome -Extra X chromosome in males (extra female chromosome) -Tall and slim -few pubic hair, facial hair, and underarm hair Turner Syndrome -Missing X chromosome –short stature -sterile -lack of ovarian development -poor breast development, constriction of aorta, web of skin Meiotic Disjunction: fail to separate in Meiosis 1 resulting in an extra or one less chromosome in some gamete cells Deletion: Parts of the chromosomes missing –Cri Du Chat –Deleted region, results in sharpen larynx: cry sounds like a cat meow Translocations: parts of chromosomes break off and attach to others –Philadelphia chromosome -Chromosome 9 and 22 mismatches, resulting in chromic myelogenous leukemia Translocations –SRY: region of Y chromosome that makes a man a man -translocation, made it’s way onto an X chromosome, in a girl, makes her like a man. Gregor Mandel – Heredity laws Genes: parts of chromosomes that govern a trait, makes proteins that defines traits Allele: alternate form of a gene. E.g. Gene for height, allele for tall or short Genotype: actual genetic information and what it says Phenotype: the way the trait looks e.g. blue eyes Sperm cell with a blue eye allele (a) on homologous chromosome 5 and egg cell with brown eye allele (A) to make Genotype Aa, and phenotype brown eyes. Dominate Trait: characteristic that is always used Recessive Trait: Present but not used unless it’s the only allele -One type of trait will be dominant and will trump the others. Homozygous Dominant: AA or aa (both the same) Homozygous Recessive: Aa (not the same) P Generation: parent generation all with homozygous genes F1 Generation: offspring from the cross of P generation, first filial generation Law of segregation: states that the inherited traits are determined by pairs of alleles and genes which Mandel called “factors”. These “factors” segregate (separate) in the gametes it one in each gamete. Law of independent assortment: States that the inheritance of one trait doesn’t affect the inheritance of alleles for another trait -Alleles pairs are passed to the offspring independently of each other -One trait doesn’t affect the inheritance of another. Inheriting blue eyes has nothing to do with inheriting blond hair. Monohybrid Crosses: -Does it with one trait at a time. -Demonstrates how dominance and recessive genes could be passed onto from one generation to another. -Dominance Genotypes are indicated with a capital letter and letter represents the dominance phenotype. -Recessive Genotypes are indicated with a lower case letter P1 Generation: BB bb F1 Generation: Bb Bb Bb Bb F2 Generation: BB Bb Bb bb <- shows mendelian ratio of 3:1 on F2 Generation -F2 Generations will always have 3:1 ratio of dominance and recessive -Mandel used pea plants and cross fertilized 2 pea plants that had purebred traits (homozygous). (Green pea and Yellow pea plants). Pea plants were picked because they were: -Commercially available at the time -Sex organs were enclosed and could self fertilized with no interactions with others -Distinguishable 2 type traits (Boolean one or the other) -Fast and easy to grow -He noticed that the first batch (F1 generation) of plants all had the dominant trait -When the plants were left to self fertilize, he noticed that the F2 Generation had some of the recessive Parent traits. Solving a Monohybrid scenario. Show the cross of 2 heterozygous guinea pigs 1) Assign alleles to phenotypes “allele for short hair is dominant” Let L stand for short hair and l stand for long hair 2) Show genotypes involved in the cross Genotypes: Ll x Ll 3) Perform the punnett square |L|l L|LL|Ll l|Ll|ll *Sort and multiply each trait to another to form a pair of alleles 4) Unique Genotypes 1 LL, 2Ll, 1ll 5) Genotype Frequencies Ratio: ¼ LL, 2/4 Ll, ¼ ll 6) Phenotypes 1 Short Hair 2 Short Hair = 3 Short Hair 1 long hair 7) Phenotype frequencies 3 Short hair : 1 long hair Frequency: 75% short hair, 25% long hair Dihybrid Crossing -Demonstrates mendel's law of independent assortment that the inheritance of one trait doesn’t dictated the inheritance of another -In Dihybrid crossing, 2 traits are put to the test Steps to solving 1) Write a let statement for the variables for each trait 2) Write out the genotype for each parent 3) Write out all the possible gametes through similar to distributive property. -Bbee -> B*e, B*e , b*e, b*e 4) Write out all the genotypes for the other parent 5) Use punnett squares, substitute in the possible gametes for each of the squares, then cross. 8 Beyond Mendelian -Mendelian’s laws stated that multiple alleles expressed it’s own traits -3 examples proved him wrong: 1) Incomplete Dominance -Mixing a red and white flower will result in a blend of a pink flower. -Heterozygous alleles are expressed as a mix of the 2 colours. -Dominant Gene expressed as is : RR -Recessive Gene expressed with a subscript: R’R’ -Heterozygous gene : R’R F2 Generation ratio: 1:2:1 2) Co-Dominance -Contains equal amounts of both traits -Both parental phenotypes are expressed -Uses superscripts to denote them: -Dominant Genes have the same: CwCw -Recessive Genes have alternate superscripts: CR CW 3) Multiple Alleles: Blood types -ABO blood type system dictates what type of blood someone has -The type of antigens that stick onto the surface of the blood will identify the blood’s type Antigens: a molecule recognized by the immune system Antibody: fights any foreign material in the body; they link to foreign substances together to create a clump of cells. -White blood cells will recognize blood that contains the correct antigen. If the blood is of a different type and contains different antigens, this will prompt the body to produce antibodies to bind to the antigens, which will prompt the body to produce more white blood cells to engulf them. -O: ii -A: IAi , IAIA -B: IBi , IB IB -AB: IA IB -O type blood is universal, won’t get attacked by antibodies as it contains no antigens Donor Recipient O A B AB O √ √ √ √ A √ B √ AB √ Non Mendelian Inheritance Thomas Morgan: Lord of the flies √ √ -states that there are some genes that were sex linked. -recessive genes will stay on X chromosome -Since males only have 1 X chromosome, if a recessive (disease) trait is on that, there will be no dominant trait to mask it -Thus, most sex-linked diseases are on males. -Females have 2 X chromosomes, and can be masked with dominant traits -Fruit Flies have different coloured eyes that are carried through sex linked alleles -Denoted with sex chromosome XX or XY and a superscript to show their traits. Polygenic Traits -States that traits are controlled by multiple genes -traits that has continuous variation (height, skin color, hair color) Modifier Genes -genes control a pigment (melanin) which controls color. -Eye color is determined by the amount of melanin in the eye. Pedigrees -A diagram to show the inheritance of a single trait carries through families -Contains useful information that can be used to predict inheritance of that trait in the children -Symbols are used to represent males, females, affected individuals, and those who have the trait and individuals who carry the trait. Symbols: –Circle: female –Square: male –Half shaded: carries that genotype (usually heterozygous) –Fully shaded: affected (have the phenotypes) –Empty: Contains normal traits