Presentation on theme: "Chromosomes and Inheritance"— Presentation transcript:
1 Chromosomes and Inheritance Chap 15 AP BioChromosomes and Inheritance
2 Locating Genes on Chromosomes Are located on chromosomesCan be visualized using certain techniquesFigure 15.1Karyotype
3 Scientist Discoveries Morgan worked with fruit fliesBecause they breed at a high rateA new generation can be bred every two weeksThey have only four pairs of chromosomes
4 Sex Linked Trait (White Eyes) Morgan first observed and notedWild type, or normal, phenotypes that were common in the fly populationsTraits alternative to the wild typeAre called mutant phenotypesFigure 15.3
5 Fly ExperimentIn one experiment Morgan mated male flies with white eyes (mutant) with female flies with red eyes (wild type)The F1 generation all had red eyesThe F2 generation showed the 3:1 red:white eye ratio, but only males had white eyes
6 Males more often have sex linked traits Sex Linked White EyesFigure 15.4The F2 generation showed a typical Mendelian3:1 ratio of red eyes to white eyes. However, no females displayed thewhite-eye trait; they all had red eyes. Half the males had white eyes,and half had red eyes.Morgan then bred an F1 red-eyed female to an F1 red-eyed male toproduce the F2 generation.RESULTSPGenerationF1XF2Morgan mated a wild-type (red-eyed) femalewith a mutant white-eyed male. The F1 offspring all had red eyes.EXPERIMENT
7 Morgan determined that Genes that are close together on the same chromosome are linked and do not assort independentlyUnlinked genes are either on separate chromosomes of are far apart on the same chromosome and assort independentlyParentsin testcrossb+ vg+b vgb+ vg+b vgb vgMostoffspringXor
8 A linkage mapIs the actual genetic map of a chromosome based on recombination frequenciesRecombinationfrequencies9%9.5%17%bcnvgChromosomeThe b–vg recombination frequency is slightly less than the sum of the b–cn and cn–vg frequencies because doublecrossovers are fairly likely to occur between b and vg in matings tracking these two genes. A second crossoverwould “cancel out” the first and thus reduce the observed b–vg recombination frequency.In this example, the observed recombination frequencies between three Drosophila gene pairs(b–cn 9%, cn–vg 9.5%, and b–vg 17%) best fit a linear order in which cn is positioned about halfway betweenthe other two genes:RESULTSA linkage map shows the relative locations of genes along a chromosome.APPLICATIONTECHNIQUEA linkage map is based on the assumption that the probability of a crossover between two genetic loci is proportional to the distance separating the loci. The recombination frequencies used to construct a linkage map for a particular chromosome are obtained from experimental crosses, such as the cross depictedin Figure The distances between genes are expressed as map units (centimorgans), with one map unitequivalent to a 1% recombination frequency. Genes are arranged on the chromosome in the order that best fits the data.Figure 15.7
9 Crossing over The farther apart genes are on a chromosome The more likely they are to be separated during crossing overThe frequency of cross over between two linked genes is proportional to the distance between them.Linkage Maps are a genetic map based on recombination frequencies.Linked genes are on the same chromosome.New combinations of linked genes are due to crossing over.
10 Sex Determination In humans and other mammals There are two varieties of sex chromosomes, X and YFigure 15.9a(a) The X-Y system44 +XYXXParents22 +XYSpermOvaZygotes(offspring)
11 Sex Chromosomes The sex chromosomes Have genes for many characters unrelated to sexA gene located on either sex chromosomeIs called a sex-linked geneSRY gene is present on the Y chromosome and triggers male development.
12 Different systems of sex determination Are found in other organisms Figure 15.9b–d22 +XXX76 +ZZZW16(Haploid)(Diploid)(b) The X–0 system(c) The Z–W system(d) The haplo-diploid system
13 Sex Linked disordersSome recessive alleles found on the X chromosome in humans cause certain types of disordersColor blindnessDuchenne muscular dystrophyHemophiliaRed-Green colorblindness is a sex-linked recessive trait.
14 X inactivation In mammalian females One of the two X chromosomes in each cell is randomly inactivated during embryonic development and remains as a dark compact body in the nucleus of female somatic cells. This is called a Barr Body
15 Female X inactivationIf a female is heterozygous for a particular gene located on the X chromosomeShe will be a mosaic for that characterTwo cell populationsin adult cat:Active XOrangefurInactive XEarly embryo:X chromosomesAllele forblack furCell divisionand XchromosomeinactivationBlackFigure 15.11
16 Barr Bodies in Female somatic cells Female Genotype?
17 Chromosomal Alterations Concept 15.4: Alterations of chromosome number or structure cause some genetic disordersLarge-scale chromosomal alterationsOften lead to spontaneous abortions or cause a variety of developmental disorders
18 Nondisjunction of sister chromatids in meiosis II Pairs of homologous chromosomes do not separate normally during meiosisGametes contain two copies or no copies of a particular chromosomeFigure 15.12a, bMeiosis INondisjunctionMeiosis IIGametesn + 1n 1n – 1n –1nNumber of chromosomesNondisjunction of homologouschromosomes in meiosis INondisjunction of sisterchromatids in meiosis II(a)(b)
19 AneuploidyResults from the fertilization of gametes in which nondisjunction occurredIs a condition in which offspring have an abnormal number of a particular chromosome
20 Results of Nondisjunction If a zygote is trisomicIt has three copies of a particular chromosomeIf a zygote is monosomicIt has only one copy of a particular chromosome
21 PolyploidyIs a condition in which there are more than two complete sets of chromosomes in an organism
22 Alterations of Chromosome Structure Breakage of a chromosome can lead to four types of changes in chromosome structureDeletionDuplicationInversionTranslocation
23 Chromosome mutations Figure 15.14a–d A B C D E F G H Deletion DuplicationMNOPQRInversionReciprocaltranslocation(a) A deletion removes a chromosomalsegment.(b) A duplication repeats a segment.(c) An inversion reverses a segment withina chromosome.(d) A translocation moves a segment from one chromosome to another,nonhomologous one. In a reciprocal translocation, the most common type,nonhomologous chromosomes exchangefragments. Nonreciprocal translocationsalso occur, in which a chromosometransfers a fragment without receiving afragment in return.
24 Down syndromeIs usually the result of an extra chromosome 21, trisomy 21Figure 15.15
25 Aneuploidy of Sex Chromosomes Klinefelter syndromeIs the result of an extra chromosome in a male, producing XXY individualsTurner syndromeIs the result of monosomy X, producing an X0 karyotype
26 Certain cancers Are caused by translocations of chromosomes Cri du chatIs a disorder caused by a deletion in a chromosomeFigure 15.16Normal chromosome 9ReciprocaltranslocationTranslocated chromosome 9PhiladelphiachromosomeNormal chromosome 22Translocated chromosome 22
27 Genetic DisordersPhenylketonuria PKU- autosomal recessive, can be controlled by regulating dietHuntington’s- dominant single allele, does not appear until 35-45yrs of age. If one of your parents is diagnosed what is the probability you will have it?Tay-Sachs disease (autosomal recessive)- can’t break down lipids and this affects brain developmentSickle Cell Anemia (autosomal recessive)- caused by a substitution of the wrong amino acidCystic Fibrosis- defect in the membrane proteins that normally function in Chloride ion transport
28 A pedigreeIs a family tree that describes the interrelationships of parents and children across generations
29 Inheritance patterns of particular traits Can be traced and described using pedigrees WwwwWWorFirst generation(grandparents)Second generation(parents plus auntsand uncles)Thirdgeneration(two sisters)FfffFF or FfFFWidow’s peakNo Widow’s peakAttached earlobeFree earlobe(a) Dominant trait (widow’s peak)(b) Recessive trait (attached earlobe)
30 PedigreesPedigree a diagram of a family tree showing the occurrence of heritable characters in parents offspring over multiple generations.Can also be used to make predictions about future offspring
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