Presentation on theme: "Chapter 12 Inheritance Patterns and Human Genetics"— Presentation transcript:
1 Chapter 12 Inheritance Patterns and Human Genetics staff.tuhsd.k12.az.usChapter 12 Inheritance Patterns and Human Genetics
2 Objectives Tell the difference between sex chromosomes and autosomes Define different types of mutationsEvaluate and create pedigree charts
3 I. ChromosomesIn the early 1990’s a researchers noticed that Drosophilia melanogaster (fruit flies) had 4 chromosomes3 were the same in both males and females and 1 was differentIn the early 1990’s researchers were studying chromosomes in Drosophila melanogaster when they noticed that one pair differed in size and shape. In females the 4 pairs were of identical size and shape while in males one chromosome was shorter than the other one. Today we call them “x” and “y” chromosomes. Two X’s is a girl and an X,Y is male.house-flies.netexploratorium.edu
4 2 Types of ChromosomesSex chromosomes contain genes that determine the sex of an individual (“X” or “Y”)Males decide the genderAutosomes-all the other chromosomes that are not involved in gender determinationCause about half of all genetic diseasesWe know that in humans girls have 2 X chromosomes and boys have an X and a Y. In other animals like chickens the males have two identical sex chromosomes while the females are the ones who have two different ones. Plants lack sex chromosomes entirely because they are asexual having both male and female parts.Sperm have a 50/50 chance of giving an X or a Y chromosome while eggs only have an X, making that the only thing they can pass on.
5 II. Linked Traits Pair of genes that are inherited together They are located in the same chromosome and very close together.Crossing over is the exchange of pieces of DNA between homologous chromosomes.graphicshunt.com
6 Sex-linked Genes and Traits Refers to a trait that is coded for by an allele on a sex chromosome (X or Y)More X-linked traits than Y-linked traits because the of the size differenceMales who have an X chromosome that carries a recessive allele will exhibit the sex-linked traitFemales have less of a chance expressing an X linked disease because they have 2 X- chromosomesFemales have less of a chance expressing the trait because if they get a dominant trait and a recessive trait only the dominate trait will show. However, if the female has a son she has a 50% chance of passing along the recessive trait to him. Females can never get a Y-linked disease. Why do you think this is?karakalpak.com
7 Mutations Germ-cell – occur in the gametes Effect the offspringSomatic-cell – occur in an organisms body cellsCan not be inherited-results in things like leukemia or skin cancerLethal – cause death, often before birthBeneficial – help the organism survive and reproduceWhat is a mutation? Change in the nucleotide sequence of DNAGerm cell – don’t normally affect the individual carrying it but will be passed on to the next generationSomatic cell- a person who spends to much time suntanning might develop a mutation in a skin cell.Lethal – implies that the individual will not live long it could be months or years depending on the mutation. It can inhibit the individual from being able to perform vital functions. An example is Turners syndrome- the individual survives but is infertile so in a sense it’s lethal because their genes can not be passed on.Beneficial- pandas appear to have 5 thumbs but their thumb is actually an extension of a wrist bone. This helps them keep their grip on bamboo and gives an anvantage over other pandas who don’t have this mutationPenguins – have flightless wings and small legs not the greatest on land but masters of the waterphotography.nationalgeographic.com
8 Chromosome Mutations Change the structure of the chromosome Deletion and InsertionLoss of nucleotide bases or an addition of themAn example of an insertion is Huntington’s disease, the codon CAG is normally repeated times within your DNA but in people who have this it is repeated times. Normally starts when you are an adult and it is a degenerative disease in which parts of your brain waste awaybiology-online.org
9 Inversion Translocation A piece of one chromosome breaks off and attaches to a nonhomologous chromosomeA piece of the chromosomebreaks off and flipsaround backwardHomologous chromosomes occur in pairsNonhomologous chromosomes are differentactivars.comstaff.jccc.net
10 NondisjunctionThe chromosomes don’t separate during meiosis so one gamete receives 2 copies and the other receives none.
11 2 Types of Nondisjunction Trisomy – an extra chromosome in every cellMost of these disorders make it very difficult for the individual to surviveTrisomy 21-down syndromeTrisomy 18 &13-normally die before age 1Monosomy – absence of 1 chromosomeTypically lethal to embryonicdevelopmentTurner’s syndromeTrisomy is named after the chrosome which is tripled examples include Trisomy 18 & 13 have severe mental retardation and health problems involving almost every organ. Trisomy 22 is the most common cause for miscarriage. Trisomy 13 is Patau syndrome – mental retaredation, eyes may fuse together, heart defectsTurner’s syndrome- affects the development of girls, they are normally short and their ovaries don’t work properly making them infertilecdadc.com
12 Gene Mutations Point mutation – change within a single gene Substitution – one nucleotide replaces anotherFrameshift mutation – if some nucleotides are deleted the entire segment of DNA moves down changing the codons for amino acidsDetrimental to the proteins functionInsertion mutation – one or more nucleotides are added which can result in a frameshift mutationA frame shift mutation occurs when a deletion or substitution appear in a part of the DNA that codes for an amino acid
13 Example of Substitution Sickle Cell Anemia: only 1 amino acid is substituted to produce the sickle shapeRecessive trait that prohibitsHemoglobin from binding correctlyTo the red blood cellunitedhealthdirectory.com
14 Frameshift MutationChanging one letter completely alters the codon sequencestaff.um.edu.mt
15 Examples of gene mutations Substitution:Original – the fat cat ate the wee rat.Mutation - The fat hat ate the wee rat.Insertion:Original: The fat cat ate the wee rat.Mutation: The fat cat xlw ate the wee rat.Frameshift:Mutation: The fat caa tet hew eer at.
16 1. Below is the base sequece for the normal protein for normal hemoglobin and sickle cell: Normal: GGG CTT CTT TTT Sickle: GGG CAT CTT TTTIs this a point or frameshift mutation? Explain.2. Delete the first H in the following sequence and regroup the letters in groups of three. Does the sentence still make sense? What type of mutation is thisTHE FAT CAT ATE THE RAT3. Name 2 chromosome mutations. How are they alike? How are they different?4. Using the sequence ATT GCA AAG GGT. Give an example of a deletion, insertion, and substitution. Circle the change you have made.5. What is the difference between sex chromosomes and autosomes?
17 List of Genetic Disorders – Pick 1 for your project ThalassemiaMarfan syndromeBreast CancerHemophiliaCri du ChatPolydactylyMaple Syrup urine diseaseTurner SyndromeKlinefelter's syndrome,(XXY syndrome)Super males (XYY)Patau syndromeAlbinismHuntington’s DiseaseDown’s SyndromeCystic FibrosisDuchenne musculardystrophySickle Cell AnemiaTrisomy 18 (Edwards)Tay-Sachs diseaseColor blindnessPKU (Phenylketonuria)Fragile X syndrome
18 II. PedigreesDiagram that shows how a trait is inherited over several generations
19 Reading Pedigrees A square represents a male A circle represents a femaleA square represents a maleIf the circle or square is filled in that means the individual has the traitHorizontal lines indicate marriage or having childrenVertical lines show offspring
20 Practice ProblemsIs the mom or dad in generation I affected by a trait?How many offspring are shown in generation II?How many daughters & sons in generation II?How many have the trait?How many offspring does daughter #1 have?
21 Patterns of Inheritance Autosomal Dominant TraitsPassed on to sons or daughters even if only one parent has the geneAffected individuals who mate with an unaffected individual have a 50% chance of passing on the gene as long as they are not homozygous for the traitCan appear in males and females equally
22 What is the genotype of #9? What must the genotype of the parents be to produce a child #7 who is unaffected?What is the genotype of #9?What are the genotypes of the 3 children in the third generation?#7 = heterozygous#9 – heterzygousThird generation – homozygous recessive
23 Recessive PedigreesIn order to be passed on both parents must have the geneTraits can be passed on if both parents are “carriers” of the traitHave the trait but it isn’t expressed because they also have the dominant traitAn individual who is infected may have parents who are notIf both parents are affected, all of their children will be affected
24 Carriers for Autosomal recessive traits We know this trait is recessive because neither parent expresses it but they have a child who has it. This makes them both carries of the allele because they both passed the recessive allele down. The other child got at least one of the dominant alleles from the parents but we can’t tell whether he is homozygous dominant for the trait or recessive.
25 Recessive PedigreeIf individuals in generation 3 have more children- will they be affected?Can Individual #8 in gen. 3 have any unaffected children?Can individual #9 in gen 3 have affected children?All children of individuals 2 and 3 will be affected#8 can only have unaffected children if they mate with someone who has a dominant allele#9 yes because we can’t tell if they are homozygous for the trait or a carrier
26 Sex Linked Traits Located only the sex chromosomes (X and Y) More frequently expressed on males than femalesY-linked is male onlyX-linked –passed from mother to sonMainly expressed in malesDaughters are carriers
27 X-linked Traits Traits that are on the X chromosome Males are affected more than femalesColor blindness is an X-linked recessive disorder passed from mother to sonColor blindness is an x-linked recessive disorder, women carry the gene but do not express it because they have 2 copies of the X chromosome. Pass it on to their sons because they get only 1 X chromosome. normal vision see this as 29, red/green see it as a 70.Those with normal vision will see this as a 5 and those who are color blind will read it incorrectly or not at allNormal is 15 color blindness is 17
28 X-linked recessiveEvident in males because they only have 1 X chromosomeWomen are rarely affected because they have 2 X chromosomes-better chance of not getting itIf the father has the mutated gene all of his daughters will have itIf males get the mutant gene then they will have the trait. Girls will be carriers unless the mother is a carrier and the father has the diseaseExample is duschenne muscular distrophy
29 X-linked Dominant No transmission from father to son All daughters of the affected male will have itOnly 1 dominant allele is needed for the trait to be expressedWhat is the genotype of #2 in generation II?
30 Genetic Disorders Diseases that have a genetic basis Researchers have found that most traits are Polygenic – influenced by several genesSkin color – combination of 3-6 genes which control the amount of melanin in the skinComplex characters – influenced by both genes and environmentHeight, certain diseases such as breast cancerBreast cancer can run in families, but environmental factors include a diet high in saturated fatcosbiology.pbworks.com
31 Incomplete DominanceDisplaying a trait that is intermediate of the two parentsWavy hair comes from one parent having straight hair and one parent having curly hairRed flower and a white flower produce a pink flowerdoctortee.com
32 Sex Influenced TraitMales and females can show different phenotypes even when they share the same genotypeEx: Male pattern baldness – the allele is dominant in males but recessive in females due to the higher testosterone levels in males
33 Single-Allele TraitsTrait controlled by 1 allele-dominant or recessiveRecessive ExamplesCystic Fibrosis-most common lethal diseaseSickle-cell anemia-blood disorderAlbinism- lack of color pigment in skin, hair, and eyesDominant ExamplesHuntington’s Disease- degradation of the brainPolydactly- presence of a sixth digitAchondroplastic dwarfism-dwarf size
34 Detecting Genetic disease Amniocentesis – technique used to detect genetic disorders in a fetusChrionic villi sampling – takes some cells derived from the placentaTreatments depend on the specific diseaseThe do this by removing some of the amniotic fluid from the sac that surrounds the fetus between the 14th and 16th week of pregnancy. This allows them to look at the chromosomes and proteins in the fluid. Carries a slight risk of miscarriage.Sample taken between the 8th -10th week