Presentation on theme: "INHERITANCE PATTERNS AND HUMAN GENETICS Chapter 12"— Presentation transcript:
1 INHERITANCE PATTERNS AND HUMAN GENETICS Chapter 12
2 Quick review…Genetics is the field of biology devoted to understanding how characteristics are transmitted form parents to offspring.
3 Generations:P Tall x ShortF1 Tall (tall is dominant)F Tall : 1 shortThe DOMINANT factor/gene masks the effect of the other factor in the F1 generation.Use CAPS ex. T for tallThe RECESSIVE factor/gene’s effect can only be seen in the P generation or F2 generation when the DOMINANT gene is absent.Use lower case ex. t for short
4 MENDEL’S 2 LAWS: #1 LAW OF SEGREGATION: A pair of factors is segregated, or separated, during the formation of gametes.Factors for different characteristics are distributed to gametes independently.#2 LAW OF INDEPENDENT ASSORTMENT:
5 PHENOTYPE is the physical appearance of that organism. Ex. Tall or shortGENOTYPE is the genetic makeup of the organism.TT = homozygous dominantTt = heterozygoustt = homozygous recessiveMENDELIAN INHERITANCE- DOMINANCE…. 2 phenotypes only.If someone has the dominant phenotype but you aren’t sure ofTheir genotype… use a pedigree (humans) or do a test cross.
6 Other Patterns of Inheritance: Incomplete Dominance- blending seen in heterozygote (ex. pink flowers, brown hair)Codominance- both dominant and recessive phenotypes seen in heterozygote. (ex. type AB blood, roan horse fur color)Polygenic- more than 1 gene determines the phenotype. (Ex. Eye color, Hair color aabbcc)Multiple alleles- more than just 2 alleles(Ex. Blood type = A allele, B allele, O allele is recessive.)
7 EX. Polygenic Inheritance- when the trait is controlled by multiple genes so many phenotypes are possible.AaBbCc x AaBbCcHuge variety in possiblePhenotypes of the offspring- skin, hair, eye color- foot size- nose length- height
8 Multiple alleles- trait controlled by three or more alleles. -Ex.ABO blood groups:- TYPE A- TYPE B- TYPE AB Shows Codominance!- TYPE O
9 The process of using phenotypes to deduce genotypes When someone has the DOMINANT phenotype you are uncertain of their genotype.TT or TtWhen someone has the recessive phenotype you can be sure of their genotype.tt
10 DIRECTIONS:For each of the following single gene/ Mendelian traits, write your phenotype on the line.Write as much of your genotype as you can be certain.- both alleles if RECESSIVE (rr)- one allele if DOMINANT (R __)Repeat the process by studying two blood relatives (parents work the best)Use a pedigree.
32 LIST OF STRANGE MENDELIAN TRAITS Ear wigglingMisshapen toes or teethInability to smell musk or skunkLack or teeth, eyebrows, nasal bones or thumbnailsWhorl in the eyebrowTone DeafnessHairs that are triangular in cross-section or that have multiple hues (colors)Hairy knuckles, palms, soles, or elbowsEgg-shaped pupilsMagenta urine after eating beetsSneezing fits in bright sunlight.
33 DNA in chromosomes contain information to make proteins. Geneticists use their knowledge of DNA and the way chromosomes behave to study how traits are inherited and expressed.
34 The parent’s genotype can be a gene pair of either:- TT homozygous dominant- tt homozygous recessive- Tt heterozygousThe parent can make gametes (sperm or eggs), through the process of MEIOSIS, that have either one or the other of the gene pair in it.
35 SEX DETERMINATION MORGAN’s Fruit fly (Drosophila) breeding experiments ofthe 1900’s revealed theidentity of sex chromosomes.In males they were differentXY; in females they were thesame XX.The other chromosomes(22 in humans) are AUTOSOMES.
36 The male determines the sex of the offspring… <--The FEMALE XX can only make X gametes.<--The MALE XY can make either X gametes or Y gametes.
37 SEX LINKAGE traits caused by genes found on a sex chromosome X-LINKED GENES:Genes located on the X chromosome.Women can be carriers.Ex. gene for ALD (Lorenzo’s Oil)Y-LINKED GENES:Genes located on the Y chromosome.Only males show these traits.Ex. SRY- triggers male development of testis.
38 Males exhibit X-linked traits more often than women because they only have ONE X chromosome. Females have two XBXb or sex linked genes.Females can be “carriers” of the bad gene yet not show the disease..Males only have one X or sex linked gene since they are XbY.Males have a higher chance of having the condition than if it were on an autosome.THERE IS NO HETEROZYGOUS for men.
39 X-linked Examples: Eye color in Drosophila Red-green colorblindness Male Pattern BaldnessHemophiliaDuchenne Muscular DystrophyALD (adreno leuko dystrophy)
40 What do you see in the circle? Do your bruises look like this?
41 If a carrier (woman) for hemophilia marries a normal man, what are the chances of having kids who are hemophiliacs? Who are not? What if the man is a hemophiliac???????
42 LINKAGE GROUPSGenes located on the same chromosome are said to be linked.Linked genes tend to be inherited together.Examples: Hair color and intelligence are linked in humans.fur color and deafness in cats are linked.
43 I’m kidding about intelligence and hair color being linked. But if they were linked…What would the phenotype(s) be of children of a dumb,blonde & smart,brunette
44 smart,brunette If that smart,brunette had kids w/ a dumb,blonde What kinds of kids could they have?What is the probability of each?
46 Linked genes result in traits that tend to be inherited together… If you do a test cross of yourHeterozygote you can see if the genesAre linked (5:5:1:1) or not (1:1:1:1).If the intelligence and hair color genes were linked, we’d only see smart-brunettes and dumb-blondes. (HA HA)So, since there are smart blondes- are these genes on separate chromosomes or on the same chromosome yet separated by crossing over?????
47 Chromosome maps can be created by conducting breeding experiments. Linked genes that separate by crossing over X% of the time are X map units apart.Compare 4 phenotype inheritance to 2 phenotype inheritance.Genes can now be placed on a chromosome in some order.
48 Genes W and Z separate by crossing over 20% of the time. Genes W and X separate by crossing over 5% of the time, andgenes Z and X are separated by crossing over 25% of the time.CONSTRUCT A CHROMOSOME MAP.Z W XI I--5--I
49 Mutations, Disease, & Human Mendelian Traits Where they occur/ significance.Types: Chromosome or GeneDiseases & Inheritance Patterns.Using Phenotypes to deduce Genotypes
50 Germ cell mutationoccurs in the gametesdoes not effect the organismmay be passed on to offspring if fertilizedSomatic mutationoccurs in the organism’s body cells & can affect the organismex. Skin cancer & leukemiaare not passed on to offspringLethal mutationcauses death (often before birth)is not passed on if death occurs before reproductionBeneficial mutationresult in phenotypes that are beneficial.beneficial phenotypes lead to increased reproduction.
51 Mutation: a change in the DNA sequence. A) chromosome mutations (affects many genes)B) gene mutations (one gene)A) Chromosome mutations:Cross over errors:Deletion- loss of a piece due to breakage.Inversion- a piece is attached upside down.Translocation- a piece reattaches to a non-homologous chromosome.Segregation Error:Nondisjunction- failure of homologous chromosomes to separate during meiosis.ex. Down Syndrome = Trisomy 21 (egg usually has 2 of #21)
53 B) Gene mutations/ point mutations- are nucleotide differences.Substitution- one nucleotide is switched for another.- ex. sickle cell anemiaFrame shift mutations- occur when nucleotides are added or removed either more or fewer than 3 nucleotides at a time.- addition- deletion
55 INHERITANCE OF GENETIC DISEASES follow different Patterns of Inheritance Single allele DominantSingle allele recessiveX-linkedSex influenced
56 PEDIGREE ANALYSIS Humans have about 100,000 genes. Most studies are of disease-causing genes.- easy to track through generations..A pedigree is a family record that shows how a trait is inherited over several generations.
57 Single allele DOMINANT- need only one gene to have the disease. - huntington’s disease (1/10,000) Hh- dwarfism Dd- cataracts Cc- polydactyly PpPATTERN: effected individuals in every generation of both male and female sex.
58 Single allele recessive- The individual needs two genes to have the disease. Albinism aaCystic fibrosis (1/200 whites) ccPhenylketonuria (1/1800) ppHereditary deafness ddSickle cell anemia (1/500 African-Americans) sc scTay-Sachs disease (1/1600 European Jews) ttPattern: 2 healthy parents have effected child of either sex.
59 X-Linked- women need two genes, men need only one gene. - colorblindness XcXc XcY-hemophilia (1/7000) XhXh XhY-muscular dystrophy (1/10,000) XdXd XdY-Icthyosis simplex-ALDPattern: more common in males,Can kip generations.