Genetics Exam 1 Study Guide Mitosis and Meiosis Mitosis produces two genetically identical daughter cells Meiosis is the production of gametes One diploid cells divides twice and forms 4 haploid cells Each of the four daughter cells gets one chromatid from each pair of homologous chromosomes o First division homologous chromosomes find each other within the cell tetrads form and crossing over occurs at the chiasmata aka chromosome recombination Homologous chromosomes now freshly recombined separate into different daughter cells o Second division Sister chromatids are separated into different daughter cells creating 4 haploid genetically different gametes Cell cycle o Interphase the cell is preparing for mitotic division G1 phase the cell is freshly out of mitosis Normal diploid number of chromosomes S phase the cell replicates its DNA The number of DNA molecules doubles but the number of chromosomes remains the same G2 phase cell prepares itself for division The number of DNA molecules remains doubled o Mitosis the parent cell divides creates two identical daughter cells Prophase genetic material condenses into chromosomes Metaphase The Chromosomes line up along the midline of the cell Anaphase Sister chromatids are separated at the centromere and moved to the poles of the cell Telophase nuclear membranes reform around the two sets of chromosomes at either pole of the cell Cytokinesis the cytoplasm of the cell is halved and the cell is cleaved into two independent daughter cells Diploid vs Haploid o Diploid A diploid organism has paired chromosomes one from each parent o Haploid a cell that has half the usual number of chromosomes such as a post meiotic gamete Homologous chromosomes Chromosomes that are the same size and code for the same proteins but differ in what alleles they have Between two homologous chromosomes they may both code for pigment but one may code for black pigment and the other for red pigment o Non homologous chromosomes code for different proteins entirely They may also differ in size Terms o Recombination The rearrangement of genetic material Specifically refers to the crossing over of chromosomes during meiosis o Crossing over A process during meiosis I in which homologous chromosomes exchange equal segments of each other This is essential for genetic variation and is fundamental to independent assortment Occurs in prophase I of meiosis I o Tetrad either 2 homologous chromosomes OR 4 homologous chromatids the complex formed during prophase I of meiosis I in which a pair of homologous chromosomes overlap each other at a certain locus and trade genetic sections o Chiasmata The point where two homologous non sister chromatids exchange genetic material during crossover in meiosis I Mendel s Principles and Probability Mendel s Postulates Terms o Each trait is controlled by a pair of factors we know these as genes o There are two factors of a trait one Dominant and one Recessive we know these as alleles o During gamete formation the paired factors segregate randomly alleles on homologous chromosomes segregate randomly o Genes for different traits are inherited independently genes on different non homologous chromosomes assort independently into gametes o Phenotype the physical expression of a trait o Genotype the genetic makeup of an individual o Allele Alternate forms of a gene o Homozygous both alleles for a trait are the same o Heterozygous two different alleles for a trait are present o Dominant a dominant allele overrides the recessive allele A dominant allele will be expressed even if a recessive allele is present o Recessive Will be masked by a dominant allele If an individual is homozygous recessive then the recessive phenotype will be expressed o True breeding homozygous for a trait If you mate two true breeders together you will get out the same genotype as the parents o Parental generation the two individuals who were mated to produce offspring o F1 generation the first products of the parental mating o F2 generation the products after the F1 generation was mated with its own genotype o F1 hybrid the product of a cross in which the parents were different genotypes o Monohybrid cross when two parents who are heterozygous for a single trait are mated o Dihybrid cross two parents who are heterozygous for two traits are mated AaBb x Aa x Aa AaBb Product vs Sum Rule o Product Rule the probability that things will happen together Aka the AND rule Ex what is the probability that the child will be albino AND a girl Multiply the probability that it s a girl by the probability that they will have an albino offspring o Sum Rule the probability that an event will occur at all taking into account all the different pathways Aka the OR rule Ex an individual can have three children what is the probability that one of them is albino The first child could be OR the second could be OR the third Add the probability of the first being albino to the probability that the second is albino to the probability that the third is albino Ratio Tips Tricks o 9 3 3 1 ratio means both parents were heterozygous o 3 1 3 1 means A B x A bb o 1 1 1 1 means one parent was heterozygous and one parent was completely recessive Pedigree Tips Tricks o First decide if the trait could be dominant or recessive Secondly decide if it could be X linked or autosomal o In X linked recessive Affected mothers pass it to ALL sons o X linked dominant Affected fathers pass to ALL daughters Affected mothers pass to half of all sons Chi Squared Tips Tricks o p 05 accept the null hypothesis there is no significant difference between the observed data and the ratio you tested for in the chi squared o p 05 reject the null hypothesis there IS a significant difference between the observed data and the ratio you tested for o Chi Squared formula observed expected 2 expected observed expected 2 expected Extension of Mendelian Genetics Terms o Codominant When two alleles of a gene are fully expressed For example a flower that has allele W which codes for red and w which codes for white A WW would be red a ww would be white and a Ww would be striped red and white because both alleles are expressed o Partially Dominant Neither allele is dominant over the other The heterozygote in an intermediate A carnation codes for BB which is deep purple bb which is white and Bb which is lavender o Multiple Alleles The norm not the exception in genetics Multiple ellels refers to a situation in which there are more than two alleles
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