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Copy of AP Bio- Mendelian Genetics 2: Extensions to Mendelian Genetics
Transcript of Copy of AP Bio- Mendelian Genetics 2: Extensions to Mendelian Genetics
Revisited Sex-Linked Traits
Influence Incomplete Dominance CoDominance Multiple Alleles More Than 2 Choices Traits linked to the sex chromosomes or a particular sex. Practice Sex-Linkage Gene Linkage Epigenetics Extra-nuclear genes Sex-Linked Disorders Polygenic Inheritance Blending - in which one allele for a specific trait is not completely dominant over the other allele. A condition in which both alleles of a gene pair in a heterozygote are fully expressed, with neither one being dominant or recessive to the other. Example: Snapdragon Color Example: Roan cow & Rhododendron Very few traits are expressed in simple Dominant/Recessive relationships Many traits are controlled by more than two alleles or one locus When there are more than two alleles for a gene. When more than one gene contributes to the expression of a particular trait Example: Human A,B, & O alleles Three blood type alleles = six possible genotypes, and four different phenotypes. Example: Human Skin Color Interactions at three(?) different loci leads to a wider variation for the trait (distributed along a bell curve). any disease or abnormal condition that is determined by the sex chromosomes or by a defective gene on a sex chromosome. Example: Some genes travel together Some traits aren't on chromosomes Linkage was first studied in the early 1900's by Thomas Hunt Morgan, a biologist who worked at Columbia University.
His lab (and its grad. students) laid the foundation for physically locating genes on chromosomes Refers to genes that are on a sex chromosome.
Males will show sex-linked traits at a higher frequency than females (why?)
First discovered in fruit flies. The white eye mutation is on the fruit fly X chromosome The X chromosome in humans has many genes. The Y chromosome has very few Map of Y Chromosome... Different modes of sex determination (fruit flies are essentially like us) Drosophila melanogaster The "Fruit Fly": An awesome model organism for genetics (why?) Refers to any genes that are on the same chromosome
Usually linked genes will travel together during meiosis.
When might they separate? How linkage affects transmission of genes Linkage Mapping Since linked genes are only separated by crossing over events, the higher the frequency of recombinant offspring for any two genes, the greater the likelihood of there being a crossing over event between them.
This correlates to a greater distance between the genes on a chromosome.
This information can be used to generate a "linkage map" of genes on a chromosome.
"Map units": indicate distance between genes on a linkage map.
1 map unit = 1% chance of crossover (and recombinant offspring) A linkage map of a Drosophila chromosome Mitochondria and Chloroplasts have their own chromosomes.
These are inherited "matrilineally"
In males, the Y-chromosome is inherited "patrilineally"* * not technically "Extra-nuclear", but still... Varriegated Leaves: A trait conferred by a chloroplast gene Mapping of Y-Chromosome mutations informs our understanding of historical human migration. Refers to any heritable trait that is not determined by DNA sequences Genomic Imprinting Methylation Some traits are only expressed if the gene is inherited from one parent or the other. Methyl groups (-CH3) are added to DNA to inactivate it.
Some evidence to suggest this methlation pattern may be heritable, and affect phenotype.
Might explain phenomena like genomic imprinting Big Questions Make Sure You Can "Dominance Hierarchy": I = I > i A B Several possible sex-linked transmission situations The interaction of an organism's genome and its environment leads to complex patterns of gene expression. The flower color of some species of hydrangea depends upon the pH of the soil (more acidic = bluer) The coat color of Arctic Hare's changes on a seasonal basis. How much of a human is a product of genes? How able are scientists to separate themselves from their culture and biases? Summing It Up: How are traits inherited?
How are traits expressed? Note: Gigantificated! Describe how each of the situations that is discussed in this presentation extends Mendelian understanding of genetics.
Use your understanding of these situations to analyze/predict data from experiments and genetics problems.
Provide examples of each of the situations described in this presentation.
Use data from crosses involving linked genes to determine the distance between linked genes on a chromosome (in map units).
Explain why most traits result from the interplay between an organism and its environment.
Illustrate how genetics illuminates the relationship between science and society. Actual Size Meiosis...makes gametes How is gender determined?: Karyotype an organized profile of a person's chromosomes Environmental vs. Genetic 22 pairs are autosomes last pair "23rd pair" are human sex chromosomes Gender -> Male's sperm ~78 genes ~1500 genes XX
XY SRY SRY An individual that has one gene for a particular recessive trait but does not express the trait Carrier: Hemophilia is a sex-lined blood disorder. People with this disease can bleed to death from a small cut because their blood does not clot. It is caused by a recessive allele. You are a normal (homozygous) female who is about to marry a hemophiliac male. What are your chances of having a child with this blood disorder?
(X = normal blood X = hemophilia) h Show, using a Punnett Square, how the sex of a child is determined. Does the egg from the mother or the sperm from the father determine the sex of the offspring? Color blindness is a sex-linked recessive trait. What is the probability that a color blind woman and a color-blind man will have: a. a normal sighted son b. a color blind daughter
(X = normal vision, X = color-blindness) c In flowers, color is an incomplete dominance trait. When the genotype is heterozygous, the phenotype is pink. Cross a pink flower with a pink flower. What will be the genotype and the phenotype of the offspring? Practice: Key: When a pure red cow is bred with a pure white bull, the F1 offspring is a roan, this means that it has both red (R) and white hairs(W).
What will be the results of a cross between a red bull and a roan cow?
Could a farmer raise a head of roan cattle that would only produce roan offspring? Explain. (R = red hairs W = white hairs) A mother has type A blood and a father has type B blood. If their baby has type O blood, what is the genotype of the parents? The family tree of genetics Pedigree Charts A pedigree is a chart of the genetic history of family over several generations.
You may use one of these to map out a genetic disease in your family.
Shows possibility of children developing diseases genetic What is a Pedigree? Female Male Constructing a Pedigree Could be NN or ___ Homozygous recessive genotype (___) autosomal dominant
A dominant condition is transmitted in unbroken descent from each generation to the next. There would be no carriers. Individuals that are _________ dominant or __________ would show the disorder Autosomal Dominant A recessive trait will only manifest itself when __________. (example: nn)
If it is a severe condition it will be unlikely that homozygotes will live to _________ and thus most occurences of the condition will be in matings between two heterozygotes (or carriers).
Carrier- Has an allele for a recessive trait but does not ______ the phenotype.
An autosomal recessive condition may be transmitted through a long line of carriers before, by ill chance two ________ mate. Then there will be a ____ chance that any child will be affected. Autosomal Recessive These must be ____ Nn nn Nn NN N n n N An autosomal recessive condition may be transmitted through a long line of carriers before, by ill chance two carriers mate.
There will be a ___ chance that any child will be affected. Autosomal Recessive Unaffected male
Horizontal Line =
Marriage (mating) Carrier
Vertical Line = offspring
A family of 2 brothers and
Identical twins Pedigree Legend In the pedigree below write the genotypes of the individuals who are labeled with numbers, using (A) to represent the dominant allele and (a) to represent the recessive allele. Start by indicating the genotypes of 5 and 6. Next, draw a Punnett Square for parents 3 and 4 and their offspring to figure out what the genotypes for 3 and 4 must be. Next, determine the genotypes of 1 and 2. Finally, determine the genotype of 7. Shown below is a pedigree chart for the inheritance of achondroplasia (ay-kon-druh-play-zhuh), a form of dwarfism. Dark circles or squares indicate individuals with achondroplasia. Examine the pedigree chart, and answer the following questions.
1. Is the allele that causes this form of dwarfism recessive or dominant?
How do you know? Using D to represent the dominant allele and d to represent the recessive allele, write the genotypes of the indicated individuals. Start by indicating the genotypes of 2, 3 and 7. Next, draw a Punnett Square for parents 5 and 6 and their offspring to figure out what the genotypes for 5 and 6 must be.
Next, determine the genotypes of 1 and 4. Body Body Body Body Body Body Body