MCB 2410: CHAPTER 3: MENDELIAN GENETICS
43 Cards in this Set
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Effect of age on gametes
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Increases chance of aneuploidy.....older=high risk for genetic abnormalities.
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Why is it a problem to have both homologs from one parent? 1
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•HOMOZYGOSITY
Øfor any detrimental alleles
•IMPRINTING
ØFor a small number of human genes expression occurs by parental origin
ØOnly one parental allele (maternal or paternal) is expressed in some cells
ØThe other allele is repressed.
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Why is it a problem to have both homologs from one parent? 2
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Can improve viability for chromosome
Any of the bad alleles that have bad information, you may have two copies of that. Everyone of us has at least one lethal allele, but we have the other allele that is functional. Got back-up from other parent.
Anywhere from 200 to 600 genes can be du…
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UNIPARENTAL DISOMY
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Both homologs from one parent as an attempt to correct aneuploidy
Duplicate one chromosome to fix monosomy
Remove extra chromosome to fix trisomy
Can remove either the paternal duplicate or the maternal chromosome (random
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Reasoning behind Uniparental Disomy
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The resulting fertilized zygote is monosomic for one of the chromosome or trisomic for one of the chromosome. Depends which stage the abnormally happens
One of the things the cells can do is they realize if there is a missing or extra copy. It may be able to replicate the DNA of the chro…
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gene
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genetic factor that helps determine a trait; often defined at the molecular level as a DNA sequence that is transcribed into an RNA molecule.
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allele
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one of two or more alternate forms of a gene
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locus
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position on a chromosome where a specific gene is located
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genotype
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the set of genes possessed by an individual organism
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homozygous
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refers to an individual organism that possesses to another by mechanism other than reproduction.
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heterozygous
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refers to an individual organism that possesses two different alleles at a locus.
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phenotype
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appearance or manifestation of a characteristic
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monohybrid cross
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a cross between two individuals that differ in a single characteristic-- more specifically, a cross between individuals that are homozygous for different alleles at the same locus (AA x aa); also refers to a cross between two individuals that are heterozygous for two female reproductive s…
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� P generation
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: first set of parents in a genetic cross
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F1 generation
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offspring of the initial parents (P) in a genetic cross
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F2 generation
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offspring of the F1 generation in a genetic cross; the third generation of a genetic cross.
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dominant
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refers to an allele or a phenotype that is expressed in homozygotes (AA) and in heterozygotes (Aa); only the dominant allele is expressed in a heterozygous phenotype.
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recessive
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refers to an allele or phenotype that is expressed only when the recessive allele is present in two copies (homozygous). The recessive allele is not expressed in the heterozygote phenotype.
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principle of segregation (Mendel’s first law)
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Important principle of heredity discovered by Mendel that states that each diploid individual possesses two alleles at a locus and that these two alleles separate when gametes are formed, one allele going into each gamete.
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� concept of dominance
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Principle of heredity discovered by Mendel stating that, when two different alleles are present in a genotype, only one allele may be expressed in the phenotype. The dominant allele is the allele that is expressed, and the recessive allele is the allele that is not expressed.
· P…
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Punnett square
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Shorthand method of determining the outcome of a genetic cross. Within the cells of the grid, the alleles in the gametes are combined to form the genotypes of the offspring
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probability
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likelihood of the occurrence of a particular event; more formally; the number of times that a particular event occurs divided by the number of all possible outcomes. Probability values range from 0 to 1.
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multiplication rule:
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states that the probability of two or more independent events occurring together is calculated by multiplying the probabilities of each of the individual events.
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addition rule
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states that the probability of any of two or more mutually exclusive events occurring is calculated by adding the probabilities of the individual events.
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testcross
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a cross between an individual with an unknown genotype and an individual with the homozygous recessive genotype.
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incomplete dominance
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refers to the phenotype of a heterozygote that is intermediate between the phenotype of the two homozygotes
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wild type
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the trait or allele that is more commonly found in natural (wild) populations.
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dihybrid cross
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a cross between two individuals that differ in two characteristics--more specifically, a cross between individuals that are homozygous for different alleles at the two loci (AABB x aabb); also refer to a cross between two individuals that are both heterozygous at two loci (AaBb x AaBb). …
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principle of independent assortment (Mendel’s second law)
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genes encoding different characteristics (genes at different loci) separate independently; applies only to genes located on different chromosomes or to genes far apart on the same chromosome.
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• Non-disjunction in Meiosis 1
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· All 4 gametes are abnormal
· Homologous chromosomes are unable to segregate
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Non-disjunction in meiosis 2
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· Failure of sister chromatids to separate
· 2 normal, 2 abnormal gametes
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Cohesions
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are responsible for holding dyads and homologous chromosomes together
· It is not until ovulation that the breakdown of the cohesion takes place
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• Shugoshin
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· is what holds homologous chromosomes together preventing non-disjunction
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Gene Duplication
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· Gene duplication is important in our immune system and the source of new genes with novel functions
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o Somatic cells
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· Makes up the cells of your body
· If there is a mutation here it will not be passed down
· Mitosis
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Germ cells
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· Heritable cells
· Specialized germ cells for reproduction
· Meiosis
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o Gregor Mendel
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· 1800's using the pea plant to derive the principal of segregation and the principal of independent assortment
· He looked at characteristics in a pea plant that are easily differentiated from each other
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Regardless of crossing over
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only one gene ends up in the haploid gamete
· Example: Asparagus urine
· A: smelly allele
· a: non-smelly allele
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True Breeding
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Homozygous Dominant by Homozygous recessive to crease True Heterozygotes
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Lethal alleles:
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•Cause death usually early in development
•Can alter phenotypic ratios
•Can be dominant or recessive
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Lethal alleles yellow mice proving 1:2:1 ratio, but hard to determine because yellow is lethal so that offspring doesnt show in physical life (cuz the homozygous dominant is lethal so the mouse is DEAD)
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The yellow allele is dominant to coat color. It is also a recessive gene (need two copies of yellow allele for death, need one other allele to counter it) Is a recessive lethal allele.
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multiple loci and alleles involved for the same traits being discussed
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For most characteristics, it is usually more than just one gene locus. There are multiple alleles for the characteristics
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Genomic imprinting
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matters which parent passes it down to you. Will determine if it is expressed or not.
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MCB 2410: CHAPTER 3: MENDELIAN GENETICS