Presentation on theme: "Other Laws of Inheritance"— Presentation transcript:
1 Other Laws of Inheritance Mendelian Genetics: characteristics controlled by dominant and recessive paired allelesMany traits follow the patterns outlined by Mendel’s Laws, many do not.
2 Incomplete DominanceOffspring heterozygous for a trait have an intermediate appearance.Neither allele is completely dominant over the otherEx: Snapdragon flowersHomozygous Red x Homozygous WhiteResults in all PINK flowers
3 Showing a Cross for Incomplete Dominance Use a capital letter for each allele since each influence trait equallyRR (homozygous red) x WW (homozygous white)What is phenotype ratio of offspring?RW x RW (heterozygous pink)How is this ratio different from the offspringof Mendel’s Monohybrid cross? (Tt xTt)
4 CodominanceIf individual is heterozygous, both alleles for gene are expressed.Ex: ChickensBlack feathers (BB) x White Feathers (WW)Offspring (BW) are checkered and have both black and white feathers
5 Try a codominant cross: Checkered (BW) x checkered (BW)Checkered (BW) x white (WW)Checkered (BW) x black (BB)
6 Ex: Roan Cattle Offspring of pure red and pure white cows Have both red and white hair
7 Multiple Alleles A gene that has more than two alleles. Each individual can only have two allelesEx: Human Blood Types
8 Possible Blood Types:A, B, AB, OThere are 3 alleles for blood type (A, B, O)A and B are codominant alleles (IA, IB)O is a recessive allele (i)
9 Six genotypes are possible for blood: IA IAIA IBIB IBIA iIB ii iWhat blood types would they have?
10 Ex: Type A (homozygous) x Type B What are the blood types of the offspring?
11 IB IB x IA IA IA i x i i IA IB x i i Try a Cross: What blood types do the offspring have?IB IB x IA IAIA i x i iIA IB x i iIf a Type A mother and a Type B Father produce a type O child, what are the parent’s genotypes?
12 Environmental Influences on Gene Expression Ex: temperature, nutrition, light etc.Ex: Coat color in Himalayan rabbitsBlack fur present only on areas of body that are colder. (ear, nose, feet and tail)
13 Ice Pack placed on fur = fur turns black If rabbit kept in warm environment, all fur is white.
14 Genetic Research and Testing To study genes for different traits it is best to use an organism that grows and reproduces quickly an produces many offspring.Can do controlled breeding experimentsCan do forced “inbreeding”Ex: Drosophila melanogaster (fruit fly)
15 Genetic Tests Test Cross: To determine if an individual is homo or heterozygous for a trait.Breed to a homozygous recessive.Ex:Drosophila: red eyes dominant over white.To see if red eyed fly is hetero/homo, breed to white eyed fly
16 Sex Determination Humans have 23 pairs of chromosomes 22 pairs are autosomes1 pair are sex chromosomesThese pictures are called karyotypes!I’m a BOY!I’m a GIRL!
17 Sex Determination XX = female, XY = male Males can give Y chromosome or X chromosomeFemales can only contribute XThere is always a 50% chance of being boy or girl
18 Sex Linked TraitsIf allele is found on an X or a Y chromosome it is inherited differently in males and females.Ex:Calico CatsColor BlindnessHemophiliaDuchenne Muscular Dystrophy
19 Calico Cats: (Codominant X Linked Trait) X chromosome has gene for black or orange fur (codominant)Only females can be “Calico” XBlackXOrangeMales can only be Black or Orangethey have only one X chromosome and one YI’m always a girl!
20 Colorblindness: (Recessive X linked trait) Certain colors cannot be distinguished from others (usually red or green)Most often seen malesFemales are more likely to be “carriers”Father cannot pass gene to son, only mother
37 Crossing Over and Linked Genes Crossing Over: homologous chromosomesline up during synapsis and exchangematerial.Increases variation in offspring.
38 Sometimes linkedgenes will separatewhen crossing overoccurs.The closer genes areon the chromosome,the less chance theywill be separated duringcrossing over
39 Autosomal Genetic Disorders Caused by defective alleles on autosomesCan be recessive or dominant
40 Sickle Cell Anemia: (Autosomal recessive) Red blood cells have a sickle shapeVery fragile and break easilyClump up on blood vessels (causing pain)
41 Reduces oxygen carrying capacity of red blood cells Caused by a single flaw in geneOne nitrogenous base in DNA sequence is differentCause wrong amino acid in protein chain for hemoglobin, changing it’s shapeHemoglobin doesn’t transport oxygen as well
42 Mostly found in people of African American descent (1 in 500 births heterozygous)If disorder has negative effects why so common in population?Malaria is a deadly disease common in AfricaHeterozygous individuals for sickle cell have malarial resistance, more likely to survive than people who aren’t carriers.I spread malaria!
43 Phenylketonuria (PKU):(Autosomal recessive) Enzyme that breaks down amino acid phenylalanine doesn’t functionChemical builds up in system and eventually forms substances that can damage the brain and cause mental retardationCan test for it at birth and treat with a low phenylalanine diet
45 Tay-Sachs Disease: (Autosomal Recessive) Incurable inherited disorder that damages the brainEnzyme doesn’t function that helps breakdown lipid in brain.Brain tissue deterioratesMost often found in eastern European JewsDeath occurs several years after birth
46 Gene-Chromosome Theory Explains the hereditary patterns that Mendel and others observed.The genetic characteristics of an organism are determined by the genes for different traits present on their chromosomes.
47 MutationsSometimes a genetic disorder is caused by a mutation of a gene.The mutation can only be passed to the next generation if it happens in a sex cell.Mutagenic Agents:Exposure to x-raysRadiationCertain chemical toxins