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Genetics Exam 2 Study Guide, Study Guides, Projects, Research of Genetics

Mercer County Community CollegeGenetics
Prof. Laura Blinderman

This document covers various topics related to genetics including Mendelian genetics, pedigree analysis, autosomal recessive and dominant disorders, multiple gene inheritance, sex determination systems, prenatal genetics, chromosomal aberrations, and more. It discusses the experiments and conclusions of Gregor Mendel, the use of Pisum sativum as a model organism, and the principles of dominance and random segregation of alleles. It also covers various genetic disorders such as phenylketonuria and achondroplasia, and the different sex determination systems in different species. The document also explains prenatal genetic testing and chromosomal aberrations that can occur spontaneously or be induced by certain chemicals or radiation.

Typology: Study Guides, Projects, Research

2022/2023

Available from 07/20/2023

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Genetics Exam 2
Gene = trait, allele = code
Mendel
1. Dominance
2. Random segregation of alleles into gametes
Transmission (Classical/Mendelian) Genetics
1. Gregor Mendel
Controlled experiments, mathematical analysis (statistics)
Pisum sativum, the garden pea
1. What makes it a good model organism?
Productive – 100s of offspring
Small
Easy – can visually see traits
Short generation time
Can self or cross fertilize
Mendel’s Conclusions
1. Genes are physical units
2 alleles per gene
1 allele inherited from each parent
2. Principle of Dominance
Dominant allele expressed in phenotype
Recessive is not
Heterozygous: P- (P for dominant allele, - for unknown allele)
3. Random Segregation of Alleles into Gametes
Meiosis
50/50 split of alleles
Pedigree Analysis
1. Who is affected and who is not?
2. What type of inheritance is the allele in the pedigree?
Autosomal recessive inheritance
1. Autosomal – not influenced by biological sex
2. Unaffected parents can have affected offspring
3. Two affected parents cannot have unaffected children
4. All people have harmful recessive alleles but a small chance that 2 people with
the same rare alleles will have children
Phenylketonuria (PKU)
1. Autosomal recessive, pleiotropy
2. Mutation in gene encoding phenylalanine hydroxylase (PAH), enzyme needed for
Phe metabolism
Pleiotropy
pf3
pf4
pf5

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Genetics Exam 2  Gene = trait, allele = code  Mendel

  1. Dominance
  2. Random segregation of alleles into gametes  Transmission (Classical/Mendelian) Genetics
  3. Gregor Mendel  Controlled experiments, mathematical analysis (statistics)  Pisum sativum , the garden pea
  4. What makes it a good model organism?  Productive – 100s of offspring  Small  Easy – can visually see traits  Short generation time  Can self or cross fertilize  Mendel’s Conclusions
  5. Genes are physical units  2 alleles per gene  1 allele inherited from each parent
  6. Principle of Dominance  Dominant allele expressed in phenotype  Recessive is not  Heterozygous: P- (P for dominant allele, - for unknown allele)
  7. Random Segregation of Alleles into Gametes  Meiosis  50/50 split of alleles  Pedigree Analysis
  8. Who is affected and who is not?
  9. What type of inheritance is the allele in the pedigree?  Autosomal recessive inheritance
  10. Autosomal – not influenced by biological sex
  11. Unaffected parents can have affected offspring
  12. Two affected parents cannot have unaffected children
  13. All people have harmful recessive alleles but a small chance that 2 people with the same rare alleles will have children  Phenylketonuria (PKU)
  14. Autosomal recessive, pleiotropy
  15. Mutation in gene encoding phenylalanine hydroxylase (PAH), enzyme needed for Phe metabolism  Pleiotropy
  1. 1 gene can have multiple different effects  PKU – slow growth, intellectual disability  1902 Archibald Garrod: Inborn Errors of Metabolism
  2. One gene: one enzyme hypothesis  Theory that one gene encodes for exactly one enzyme  This is generally but not always the case  Alkaptonuria – Black Urine Disorder, Pleiotropy
  3. Autosomal recessive
  4. Also causes black spots in the eyes  Autosomal Dominant Disorders
  5. Tend to show up in every generation  2 unaffected parents cannot have an affected child  2 affected parents can have an unaffected child  Achondroplasia
  6. Mutation in growth hormone receptor gene  Long bones don’t grow as much as they normally would
  7. Most cases are a spontaneous mutation in sperm or egg  Most people with achondroplasia don’t have a parent with it  Two Gene Inheritance
  8. Mendel's Law of Independent Assortment  Each allele for a trait is inherited independently of other alleles  What Mendel Didn’t Know
  9. Incomplete Penetrance  Penetrance – percentage of individual that exhibits a phenotype corresponding to the genotype  Polydactyly is not fully penetrant
  10. Incomplete Dominance  Allelic symbols do not specify dominance  CR^ = red color  CW^ = white color  CRCR^ x CWCW^ – all offspring are pink
  11. Heterozygote Advantage  Sickle cell allele  HbA/HbA (SS) = normal adult hemoglobin  HbA/HbS (Ss) = normal phenotype + malaria advantage  HbS/HbS (ss) = sickle cell disease  Plasmodium (protozoa) transmitted by Anopheles mosquito  Part of life cycle in RBCs  Ruptures RBCs, causes malaria
  12. Multiple Alleles

 Same genotype, expressed differently  Epistasis  A product of one gene influences the expression of another gene  Modification of dihybrid cross  9: 3: 3: 1 ratio  Dominant series  C series / rabbits  C+ = full color  Cch^ = chinchilla  Ch^ = himalayan  C = albino  X – lined Genes  Factor VIII  Alleles  Xh^ = hemophilia  XH^ = normal  Generally, when looking at a pedigree, when only men are affected it is x – linked  “criss - cross” inheritance  Morgan’s Experiment on X – Linkage  Fruit fly nomenclature  Allele key  W+ = wildtype red allele  W= mutant white allele  Wingless mutant (Wg allele) (wildtype is Wg+)  Dosage Compensation (mammals)  Having too much or too little genetic info can affect how tissues develop  Bar Bodies – one X active in every cell  X chromosome inheritance  Very early on in embryonic development, one X becomes inactive  Inactive X becomes very condensed  Epigenetic inheritance  Cells “remember” which X chromosome it had active and tells its progeny which X to use as the embryo develops  Bar Body  Every mammal cell has only one activated X  XX – one inactivated (one Bar Body)  XXX – two inactivated (two Bar Bodies)  Calicos <  Orange male = XoY  Black male = XBY  Black female = XBXB

 Orange female = XoXo  Calico female = XBXo  Y – linked genes  Not technically homologous to X chromosome, but do share some genes  Pseudo autosomal region of X and Y  Small region of code that X and Y both have  Mammalian Sex Structure Determination (Y system)  7 weeks gestation (human) embryo has bipotential gonads (have both male + female tissue)  Y chromosome signals for male sex tissue development  SRY gene  Encodes TDF  Sex determining region of Y encodes  Testes Determining Factor = a transcription factor (protein)  Y chromosome -> SRY -> TDF -> development of testes -> testosterone hormone -> sperm ducts, penis, brain “sensitization”  If no signal, typical female structures develop  Mutation in SRY: 46, XY Gonadal Dysgenesis  No TDF – gonadal tissue is minimal  Develop uterus, vagina, oviducts  Hormone therapy at puberty  46, XX Testicular Difference of Sex Development  Crossing over of SRY gene to X chromosome  Develop male characteristics  No sperm development genes  Sperm development is on Y chromosome  Chimerism 46, XX / 46, XY  Two early embryos fuse into a single embryo  Effects on development variable  Tetra gametic  4 gametes involved that fuse into one embryo  Other Sex Determination Systems  Drosophila  Ratio of X to sets of autosomes  Y not related to sex  XX / 2 sets of autosomes = 2/2 = 1 (female)  XY / 2 sets of autosomes = ½ = 0.5 (male)  ZW System (birds)  Females = ZW  Males = ZZ  Some reptiles also use the ZW system (Ex. Kimono dragons)

o 45, X (10)/ 46, XX (90)  Mosaic Down o 45, 21+ / 46 Ploidy = sets of chromosomes  Diploid – many animals, fungi, + plants  Monoploid – sterile insects (ex. Worker bees)  Tetra, hexa, octoploid – common in plants o Polyploid  Toads are tetraploid Chromosomal Aberration (chromosomal “mistake”)  Spontaneous  Induced o X – rays, certain chemicals  Can occur in gamete, embryo, or somatic cell in adults

  1. Deletions a. Cause i. Chemical, radiation ii. Unequal crossing over during meiosis iii. Spontanous b. Affect on person i. Somatic cell – cell might die or keep growing (cancer) ii. Gamete – serous effect on embryo (deletion is in every cell) c. Deletion homozygous = lethal d. Cri du chat i. 46, XY, 5p- ii. Pseudodominance
  2. Missing two copies, so whatever copy they have is forced to be expressed
  3. Duplication a. Tandem or reverse b. Somatic cell – may lead to cell overgrowth c. Gamete – can affect development d. Anencephaly i. Brain doesn’t form
  4. Inversions a. No loss of genetic material