Presentation on theme: "Unit 6 Genetics Chapters 14-15. Let me tell a story u Once upon a time* there was a monk who enjoyed gardening. He wondered why some plants were tall."— Presentation transcript:
Unit 6 Genetics Chapters 14-15
Let me tell a story u Once upon a time* there was a monk who enjoyed gardening. He wondered why some plants were tall while others were short. He also wondered why some peas were green and others were yellow. So he started experimenting in his garden…. u *1857
Basic terms u Character- an inherited feature w/multiple variations u Trait- each variant u True breeding- create all offspring with the same traits u Hybridization- mating/crossing of 2 true- breeding individuals
u Pic 14.2
Mendel’s 4 Hypotheses u 1. alternate versions of genes (alleles) account for variations in inherited characters
Mendel’s 4 Hypotheses u 2. for each character, an organism inherits two alleles, one from each parent. u 3. If the two alleles differ, then the dominant allele is fully expressed in the organisms appearance, the recessive allele has no noticable effect on the organism’s appearance.
Mendel’s 4 Hypotheses u 4. two alleles for each character segregate during gamete production u LAW OF SEGREGATION
Old Vocab reminder u Homozygous u Heterozygous u Phenotype u Genotype u Testcross- homozygous recessive + dominant trait (unk if it is homo or hetero)
Dihybrid crosses u Remember law of independent assortment – Every possible combination u What ratio of results is always produced with a dihybrid cross when homo. Dominant + homo recessive are used? u __________________
u Pic 14.7
Practice Punnett Squares u Using the human traits discussed in class, we will make up scenarios and use punnett squares to solve the problems.
Using Math to skip punnett squares 1.Know your genotypes 2.PpYyRr x Ppyyrr 3.P= purple, p= white flowers 4.Y=yellow, y=green seeds 5.R=round, r=wrinkled seeds 2. Know the question: the probability of having 2 recessive traits 3. List all genotypes that would match this result ppyyRr, ppYyrr, Ppyyrr, PPyyrr, ppyyrr
Probability lesson u 2 traits- purple or white flowers u Chance the sperm will have purple allele = ½ u Chance the sperm will have the white allele = ½ u Same for ovum (egg) u For genotype pp u ½ x ½ = ¼ probability that this genotype will form
When things aren’t so simple u Mendel used all traits that were simple dominant or recessive, this is not that common in complex organisms
INCOMPLETE DOMINANCE: Heterozygous organisms have a phenotype between that of the parents.
Common Misinterpretation u Dominant means “able to overpower” u Dominant does NOT mean good OR more common u Polydactyly is dominant over 5 digits/appendage. 1/400 in US born with it u Some types of dwarfism also dominant over average height.
Codominance- human blood groups u 3 groups based on presence of proteins u Proteins called M and N u Homozygous is M or N u Heterozygous is MN (both present)
Practice- blood type problems u Importance of blood types u Giving the wrong type can be deadly
Polygenic inheritance u Additive effect of several genes together u Quantitative characters- traits that show some point in a range instead of on/off u Human skin color u AABBCC- very dark u aabbcc- very light
Genetics and Environment u The environment can sometimes determine what phenotype shows up. u 2 flowers with the same genotype u Different acidity u results in different u colors
Multifactorial u Genetics and environments influence the phenotype
Informal Research Rubric Results will be presented and discussed in class and collected ___________ u You DO NOT need to write a formal essay for this. u Name of Inherited Disorder _______________ u Direct Known Cause of Disorder _____________ u Prevalence of Disorder ____________ u How is the disorder passed on to other individuals? _____ u What does the disorder to do the human body? _________ u Is there any treatment to help those affected by the disorder?________ u Any particularly interesting facts you want to share? ____
Inherited Disorders u Cystic fibrosis u 1/25 caucasians is a carrier u Normal allele makes a membrane protein that functions in movement of chloride ions u Defective or absent in people with cystic fibrosis u Mucus builds up in lungs, digestive tract u More bacterial infections
Untreated- fatal by age 5 Treated- live into the 20’s, some longer
u Tay Sachs disease u Dysfunctional enzyme fails to break down lipids in the brain u Infant seizures, blindness, loss of motor and mental skills u Unusually high number in pop. Ashkenazic Jews whose ancestors are from central europe u 1/3600 in that pop, 100x more than other populations
Fatal within early childhood- 5 or younger.
Sickle cell anemia u 1/400 african americans u Substitution of 1 amino acid in hemoglobin u Codominance- carriers have the sickle cell trait- get the symptoms when blood oxygen is low for a long time u Causes resistance to malaria
DOMINANT inherited diseases u ACHONDROPLASIA- u 1/10,000 people u Most people are u homozygous recessive
HUNTINGTON’S DISEASE u Degenerative disease of nervous system u No phenotype noticable until ages u Fatal, not reversible u Passed on because people have children before they know they have the disorder
INDEPENDENT EVENTS u The probability of passing on a trait good, bad, or indifferent is the same for each offspring!
Testing for Carriers u Is the future going to be like it is in Gattaca? u Should you have children if you have a 50% risk of passing on a genetic disorder? u Are you likely to inherit a disorder?
u Done at weeks into pregnancy u Identify disorders from the amniotic fluid or fetal cells that are floating in the fluid u Results take 1-2 weeks
Chorionic Villus Sampling u Done at 8-10 weeks into pregancy u Placenta cells taken and divide very quickly u Results in 24 hours
Other pre-natal tests u Ultrasounds u fetoscopy
PKU and Newborn screening u Phenylkenonuria- 1/10,000 -1/15,000 births in U.S. u Inability to break down amino acid phenylalanine u Too much of it can build up and result in mental retardation u Solution- diet low in phenylalanine
CHAPTER 15 u Chromosomal Basis of Inheritance u In 1900 scientists doing research on plants discovered that Mendel had recorded the same discoveries about inheritance 35 years earlier. u LESSON OF THE DAY- DO YOUR RESEARCH FIRST!!!!!
Chromosomal Theory of Inheritance u The genes Mendel studied have specific loci on chromosomes u Chromosomes independently assort and segregate during meiosis
The first experimental Mutant in Thomas Morgan’s experiments
Drosophila melanogaster u Fruit fly u Harmless u Breed quickly and in large numbers u 3 pairs autosomes, 1 pair sex chromosomes u Wild type has red eyes, the “normal” phenotype
SAY CHEESE!! WILD TYPE
Sex Linked Traits u White eyes in flies had to be on the X chromosome
Morgan’s Evidence u P- Male white eye mutant, Female wild type u F1- 100% red eye flies, male or female – White must be recessive u F2- 100% females red eyes, – 50% males white eyes – 50% males red eyes – Eye color trait must be on X chromosome
Punnett Square Evidence
Linked genes u Each chromosomes has 100’s or 1000’s of genes u Genes often overlap on chromosomes u Genes near each other on a chromosome are usually passed on together as a group
Genetic Recombination u Production of offspring with new combinations of traits u Parental types- offspring that have the same phenotype as parents u Recombinants- offspring with different phenotypes as parents
YyRr x yyrr Y- yellow R-round y-green r- wrinkled u Complete the punnett square to see what the seeds of the next generation will look like. u How many are recombinants? How many are the parental types?
Correct Results u 50% recombinants u Therefore 50% frequency of recombination u Any 2 genes on different chromosomes have this recomb. frequency
Linked genes can become recombinant in crossing over
Genetic maps Alfred Sturdevant calculated where genes were based on recombinant frequencies Closer together = smaller frequency of recomb. Called Linkage Maps
1 map unit= 1% recombination frequency Aka centimorgan Genes on 1 chromosome with 50% r.f. or higher are equivilent to being on different chromosomes.
Cytological maps u Show actual location of genes on chromosome based on visible traits
Mapping Human Genes: HGP I have a more updated human gene map in the classroom…but still several years old.
Sex Chromosomes u X and Y rarely cross over and do not match but count as homologous chromosomes u Gene SRY discovered 1990 u w/o SRY gonads form into ovaries u SRY is a trigger causing many other genes to operate
Not all organisms use the XY system, but they have variations in sex chromosomes to identify genders.
Sex Linked Traits-aka X linked traits u On X chromosome resulting is distinct patterns of expression in Males vs. females
Trends in Sex Linked traits u If the trait is sex linked and recessive you will see it more in males because they only have 1 x chromosome u Less common in females because they can inherit the dominant allele and hide the recessive trait
Human Sex Linked Traits u Color blindness u Hemophilia u Duchenne muscular dystrophy
X Inactivation u Females have 2 X chromosomes, but one condenses and becomes a Barr Body u Most genes on barr body are never activated u At the time of X inactivation each cell present randomly “assigns” one X to become the barr body. u Therefore not all cells show the same phenotype
How is X inactivated? u Methyl group (CH 3 ) attached to cytosine in DNA u Only one X has XIST gene (X inactive specific transcript) u Causes the DNA to be covered in RNA u Starts the inactivation u Still don’t know it all though
Chromosome errors u Nondisjunction- tetrads/chromatids fail to separate in Meiosis I or II u Aneuploidy- abnormal # chromo. u Trisomic- 3 copies of a chromo. u Monosomic- only 1 copy of a chromo. u Polyploidy- more than 2 complete chromo. Sets (common in plants)
Mutations to Chromosome structure
Specific Cases Down Syndrome- trisomy 21 Klinefelter Syndrome- XXY Turner Syndrome- XO Cri du Chat- deletion in chromosome 5, but normal 46 chromo. Chronic Myelogenous Leukemia- part of #22 switched with part of #9
More complications u Sometimes the phenotype depends on which parent provided the allele
Prader Willi and Angelman syndromes u Both caused by deletion of a specific section of #15 u Prader-Willi- deletion from father – Mental retardation, obesity, short stature, small hands and feet u Angelman- deletion from mother – Spontaneous uncontrollable laughter, jerky movements, motor skills problems, mental disabilitiesa
Genomic imprinting u Allele on one chromosome is silenced u Caused by methylation, same as X inactivation
Fragile X Syndrome u Piece of the X chromosome is dangling on u 1/1500 males, 1/2500 females u The most common genetic cause of mental retardation u More commonly inherited from mom
Passing On Mitochondrial DNA u Does not follow mendelian rules u Passed on from mother u Rare human disorders caused by this u Mitochondrial myopathy- weakness, intolerance of exercise, muscle deterioration u May contribute to alzheimers disease
u Clearly, we could spend more time on genetics! But, I have MUCH more to cover in the world of biology this year! u This is a summary of what the college boards states is on the AP exam.