Download AP Biology Study Guide Chapter 8: Monohybrid cross Law

AP Biology Study Guide Chapter 8: v Monohybrid cross Ø Law segregation Ø 3: 1 v Dihybrid cross Ø Law of independent assortment Ø 9:3:3:1 v Character Ø Gene § Color of eyes v Trait Ø Allele § Blue or brown v Parental generation – P1 Ø F1 generation is offspring P1 v Genes are particulate and are inherited according to Mendel’s laws Ø Character – observable physical feature Ø Trait – form of a character Ø Mendel worked with true breeding varieties – which plants of the same variety were crossed all offspring plants produced the same seeds and flowers Ø Mendel’s crosses § Pollen from one parent were transferred to the stigma of the other parent § Paternal generation = P § Resulting offspring = first filial generation of F1 § If F1 plants self pollinate they produce second filial generation or F2 Ø One trait of each par disappeared in the F1 generation and reappeared in F2 these traits are recessive Ø The trait appears in the F1 as the dominant trait Ø The ratio of dominant to recessive traits in the F2 was about 3:1 Ø Mendel’s observations rejected the blending theory of inheritance and supported the particulate theory Ø He proposed trait the determinants occur in pairs and are segregated in the gametes Ø Each plant has two genes for each character one for each parent Ø Diploid – two copies of a gene Ø Haploid – one copy of a gene Ø Alleles are different forms of a gene Ø True breeding individuals have two copies of the same allele and are homozygous Ø Heterozygous individuals have two different alleles Ø Phenotype – physical appearance of an organism Ø Genotype – the genetic makeup Ø Same phenotypes can be from different genotypes § 𝑝! + 2𝑝𝑞 + 𝑞! = 1 § 𝑝 + 𝑞 = 1 Ø Mendel’s first law § The law of segregation states that the two copies of a gene separate when an individual makes gametes § Each gamete receives only one copy Ø A gene is a short sequence of a larger DNA molecule Ø DNA molecules make chromosomes Ø Mendel tested his hypothesis by doing test crosses § He did this to determine whether an individual is homozygous of heterozygous for a trait by crossing it with a homozygous recessive individual Ø Mendel crossed the F1 with known homozygotes Ø Mendel’s next experiment involved § Crossing peas that differed in two characters Ø Crossing the F1 generation (all identified double heterozygotes) is a dihybrid cross Ø Mendel’s second law § Law of independent assortment states that alleles of different genes assort independently during gamete formation § This law doesn’t always apply to genes on the same chromosome but chromosomes do segregate independently Ø Probability § Joint probability – multiply by the individual probabilities (multiplication rule) § The probability to the sum of the individual probabilities (adiditon rule) v Alleles and genes interact to produce phenotypes Ø Different alleles arise through mutation – rare stable inherited changes in the genetic material Ø The wild type is the allele present in most of the population,other allels are mutant alleles § A gne with a wild type allele that is present less than 99% of the time is called polymorphic Ø A given gene may have more than two alleles Ø Multiple alleles increase the number of possible phenotypes and may show a hierarchy of dominance in heterozygotes Ø Some alleles are neither dominant nor recessive § A heterozygote has an intermediate phenotype incomplete dominance • Ex. Pink ♦ Red + white = pink F1 ♦ Red = white + pink appear in F2 § Co-­‐dominance – two alleles of a gene produce phenotypes that are both present in the heterozygote Ø Epistasis – phenotypic expression of one gene is influences by another gene v Recombinant DNA – close + cross over can or will not cause significant difference of 3:1 ratio v Genes are carried on chromosomes Ø Genes are sequences of DNA that reside as a particular site on a chromosomes – a locus (plural loci) Ø The genetic linkage of genes on a single chromosome can alter their patterns of inheritance Ø Some offspring showed recombinant phenotypes different from their parents § Genes may recombine during prophase I of meiosis by crossing over § Homologous chromosomes exchange corresponding segments § The exchange involves two chromatids of four in the tetrad – both chromatids become recombinants (each ends up with genes from both parents) Ø Recombinant offspring phenotypes (non-­‐parental) appear in recombinant frequencies • To determine the recombinant frequencies divide the number of recombinant offspring by the total number of offspring • Recombinants frequencies are greater for loci that are farther apart on the chromosome § Recombinant frequency = recombinants/total offspring Ø Recombinant frequencies can be used to make genetic maps Ø Many genes on the X chromosome are not present on the Y chromosome Ø Chromosome pairs similar in size – autosomes § Different size – sex chromosomes Ø Sex linked inheritance – inheritance of a gene that is carried on a sex chromosome Ø X linked recessive phenotypes § They appear much more often in males than females § A male with the mutation can only pass it onto daughters § Daughters who receive one X linked mutations are heterozygous carriers § Mutant phenotype can skip a generation if it passes from a male to his daughter (normal) and then to her son v Prokaryotes can exchange genetic material Ø Bacteria exchange genes by bacterial conjugation Ø Sex pilus is a projection that initiates contact between bacteria cells Ø Conjugation tube is a cytoplasmic bridge that forms between cells Ø The donor chromosome fragments and some material enters the recipient cell Ø Bacteria have plasmids – small circular DNA molecules – besides the main chromosome Ø Genes on the plastids are in categories § Metabolic tasks breaking down hydrocarbons § Involved in conjugation § Antibiotic resistance Ø Plasmids can more between cells during conjugation Ø They can § Replicate independently of the main chromosome § Add their genes to the recipient cells genome