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Week 3 Notes

by: Jessica Brown

Week 3 Notes BSCI - 30156 - 002

Jessica Brown

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This is the last bit of material that is covered for exam 1
Chi-hua Groff (P)
Class Notes
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This 5 page Class Notes was uploaded by Jessica Brown on Monday February 8, 2016. The Class Notes belongs to BSCI - 30156 - 002 at Kent State University taught by Chi-hua Groff (P) in Fall 2015. Since its upload, it has received 23 views. For similar materials see ELEMENTS OF GENETICS in Biological Sciences at Kent State University.


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Date Created: 02/08/16
Genetics Week 3 Notes Mendels First Law: Law of independent segregation  Each plant possesses two units (alleles) for each trait  The Alleles separate in the formation of gametes  Gametes contain ONE allele for each trait If you observe an individual with a dominant phenotype, what is the best way to determine its genotype? Do a test cross—cross a parent to an individual that is homozygous recessive Mendelian Inheritance  Single locus directly effects a single trait on autosomal chromosomes Laws 1. Law of independent assortment 2. Law of independent segregation **Remember these have to do with alleles NOT genes.** Independent assortment  Two alleles separate independently—four gametes result  Two genes on two chromosomes will segregate their alleles separately  Inheritance of one allele does not influence your chance of inheriting the other  This disproved the original idea of blending inheritance—where it was thought that if a short and tall plant were to be bred the result would be a medium plant. Independent assortment shows this to be untrue.  Dihybrid crosses o Have 9:3:3:1 phenotypic ratio Independent Segregation  Alleles segregate independently Pedigrees  Pedigree: a visual representation of what is occurring with the genotype and phenotype of an individual —represents a male —represents a female  A solid line between two figures represents mating.  A double line === shows relatives mating  Roman numerals represent the generations. Arabic numbers symbolize birth order within a generation  Unaffected individual: unshaded shape  Affected individual: Whole shape is shaded  Known heterozygote (Cc): Half-filled shape 3 Patterns of Inheritance 1. Autosomal recessive (homozygous recessive alleles (aa)) 2. Autosomal Dominant (Heterozygous dominant (Aa) or homozygous dominant (AA)) 3. X-Linked recessive Autosomal Recessive  Unaffected parents can have affected children o This is due to carriers (heterozygous) (Aa)  Two affected parents will only have affected children o Because they can only give the recessive alleles  Both parents heterozygotes, then the risk of an affected child is 25%  Males and Females are both equally affected Albanism—pigmentation is a dominant trait, albino is recessive  Consanguinity: two closely related family members mating o Autosomal recessive traits greatly increase when you marry with (for example) first cousins. This is due to the probability of you both being carriers Remember—alleles affect protein production. Therefore, a recessive allele contains a mutation that stops a protein from being produced which causes you to display the affected phenotype.  Dominant alleles produce too much of a protein which causes over function and you display the affected phenotype.  Too little proteintoo much protein=problems Autosomal Dominant  Can not have carriers. o This is because autosomal dominant traits only need ONE dominant allele to display the trait or have the syndrome. (this is different than autosomal recessive) o This is how acondroplasia parents can still have normal children. Because they can pass on the recessive allele. Since the dominant allele is the disease causing allele, the children can remain unaffected with two recessive alleles.  Unaffected individual: aa  Affected individual: Aa o Remember AA is typically lethal so it isn’t normally seen in a genotype  (Aa)x(aa)= 50% chance of having a kid that is affected  Affects the same number of males and females Huntingtons Disease  Autosomal Dominant Disease o H= affected h=normal  Causes damage in the brain from an accumulation of huntington protein  Symptoms begin slowly (30-50years old) o Affected people may have already had children before they realized they were affected  Progressive neurological symptoms, no treatment, die within 10-25 years after symptoms begin Sex Chromosomes Hemizygous: males only have 1 X chromosome (half) of what females have  Genes on X chromosomes: X linked  Genes on Y chromosome: Y linked  For X Linked o Possible Female Genotypes  XX, XX*, X*X* o Possible Male Genotypes  XY X*Y o The * next to the X indicates an affected allele  Males can not be heterozygous or homozygous because they are hemizygous for genes on X  Distinctive pattern of inheritance  Mother always gives X chromosome  Father gives X to a daughter and Y to a son Check out the cystic fibrosis practice problem on learn!! It will be important to have an understanding of this for the exam! Sex Determination  Males—XY o Heterogametic or hemizygous  Females—XX o Homogametic  SRY gene on the Y locus is the cause of the male pathways being turned on. Without the SRY gene the phenotype with be female.  DNA stores critical information but does nothing aside from direct what proteins are to be produced o Proteins then carry out all the functions that occur  Due to females having two X chromosomes they have double the amount of production then males o This allows dosage compensation to occur  Dosage Compensation: a process the body has to deal with over production of something o This is why females are mosaic: In somatic cells one X in every cell is inactivated and only one X remains active  This occurs randomly! So in one cell your mothers X can be on and in the next your Fathers X can be on. o Fruitflies contain dosage compensation in both males and females  Regulatory switches control this  Study Regulatory switches o Barr Body: A space in the cell that contains the inactivated X. Very dense area due to protein of the active X coating the inactive X.  Klinefelters: XXY (primarily male characteristics due to Y—SRY gene); one barr body  Turners Syndrome: X0; no barr body  Remember, sex chromosomes are the only chromosomes that you can survive only having one. One chromosome on ANY of the autosomal chromosomes is lethal  Triple X Syndrome: XXX; two barr bodies XIC region  On each X chromosome o Involved in counting of X chromosomes  XIC region houses the XIST gene o XIST gene on the inactive X is transcribed—forming RNA which coats the inactive X  Inactive X is maintained as a barr body throughout cell replication Lyons Hypothesis  One X chromosome is inactivated in somatic cells of XX females  Inactivation is random  Inactive X=barr body—maintained through mitosis ** Sex linked traits DO NOT affect males and females equally**


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