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40 Cards in this Set
- Front
- Back
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Gregor Mendel
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Father of modern genetics.
Studied pea plants; analyzed statically. --Out of this, discerned that characteristics are inherited as discrete units, known as genes. |
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Law of Dominance
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Dominate genotypes always show the trait in heterozygous offspring.
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Law of Segregation
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Demonstrated by monohybrid cross.
--Traits carried by hybrid parents separate during Meiosis. |
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Monohybrid cross
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TT X tt
Genotype ratio in the F1 is 1:2:1 --1 homozygous dominant, 2 heterozygous, 1 homozygous recessive. F1 phenotype ratio=3 tall:1 short |
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Backcross/Testcross
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A cross to determine the genotype of an organsim showing a dominant phenotype.
--Could be homozygous dominant or heterozygous. Cross dominant phenotype with an individual expressing the recessive phenotype. --It any offspring show recessive trait, the parent was heterozygous. |
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Law of Independent Assortment
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Applies to dihybrid crosses.
--Individuals that are hybrids for 2 or more traits, on different chromosomes. TtYy X TtYy Punnett square will show --Phenotype ratio- 9:3:3:1 --Genotype ratio- 1:2:1:2:4:2:1:2:1 |
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Incomplete Dominance
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Results in a blending of traits.
--Red flower (RR) X White flower (WW) produces pink (RW) flowers. Phenotype ratio- 1:2:1 Genotype ratio- 1:2:1 |
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Codominance
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Both traits are expressed in a hybrid condition.
--Horses: red (RR) X white (WW)=roan (RW) *Horse coat has both red and white hair --Humans: Type AB=person expresses both A and B surface antigens; A and B alleles are codominant. |
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Multiple Alleles
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The gene has more than 2 alleles in the population.
--E.g. in humans, there are three alleles for blood types: A, B, and O, A & B are dominant, O is recessive. --Possible genotypes: AO, AA, BO, BB, OO, AB |
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Epistasis
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(Gk. to stand above) a gene at one locus (chromosomal location) affects the phenotypic expression of a gene at a second locus.
--The allele of one of the genes may have an overriding affect on the phenotype. --The allele is said to be epistatic to the other genes. *Ex: mice coat color |
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Polygenic Inheritance
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And additive effect of two or more genes on a single phenotypic character.
Ex: human skin pigmentation and height |
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Pleiotropy
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Genes with multiple phenotypic effect.
Ex: sickle cell anemia --Ex: phenylketonuria-primary effect-toxic substances accumulate in brain-mutation also interferes w/ synthesis of melanin. 1. PKU patients often blond. |
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Expressivity
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The range of expression of mutant genes
--E.g. polydactyly-trait for more than 5 digits 1. Can range from having a separate extra digit, to just an enlargement next to the little finger or toe |
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The Environment Can Alter the Expression of Genes
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Fruit flies: vestigial wing mutation is altered by temperature- in hot environment grow normal length wings.
Humans: IQ-combination of genetic predisposition and the child's environmental surroundings. Nature vs Nurture argument |
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Linked Genes
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Genes on same chromosome are always inherited together (unless separated by crossing-over)
--E.g. crossing 2 dihybrid individuals (TtYy_ gives the same results as a monohybrid cross. 1. The gametes would carry alleles for Tall and Yellow seeds, or short and green seeds. 2. Offspring would show 3:1 ratio of Tall Yellow:short green. |
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Sex-linkage
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Genes located on a sex chromosome--Usually refers to the X chromosome.
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Map Units
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One map unit=distance on the chromosome within which crossing over occurs 1% of the time.
Greater the number of map units between genes, the greater the chance they will be separated from each other by crossing over. |
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Linkage Map
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Based on incidence of crossing over.
--E.g. if a distance between genes is: 1. Gene A to Gene B= 9 map units 2. Gene B to Gene C= 3 map units 3. Gene A to Gene C= 6 map units. The order of the genes is ACB or BCA |
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Sex Linked Traits
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All traits on the X-chromosome.
Always expressed in males. Females can be carriers: E.g. hemophilia XY x XX Son of a mother who is a carrier will have a 50/50 chance of being affected. |
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Pedigree
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Diagrams that show relationships among family members.
Can be used to trace inheritance patterns of disorders. --Males=squares --Females=circles Horizontal line connecting circle and square=mating. Offspring shown below mating. |
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Barr Body and X-Inactivation
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An inactivated X chromosome can be seen as a dark spot on the outer edge of nucleus in all somatic (non-gamete) cells in human females.
Genes on Barr body not expressed. |
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Lyon Hypothesis
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Selection of which X is inactivated is random.
Inactivation occurs by methylation (attaching CH3 group) to cycosine in the nucleotides. --Found in males with Klinefelter's (XXY) Syndrome. --Produces tortoiseshell pattern in cats. |
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Mutations
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Any change in the genome.
Random. Two types. |
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Two Types of Mutations
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Gene mutations and Chromosomal mutations
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Types of Gene Mutations
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Deletion, Duplication, Inversion, Translocation. Deletion and Duplication are frame shift mutations.
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Deletion
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Removal of chromosomal segment. Frame shift mutation.
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Duplication
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Repeats a chromosomal segment. Frame shift mutation.
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Inversion
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Segment reversal in a chromosome.
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Translocation
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Movement of a chromosomal segment to another.
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Types of Chromosomal Mutations
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Nondisjunction, Aneuploidy
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Nondisjunction
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Homologous chromosomes do not separate properly during Meiosis 1, or sister chromatids fail to separate during Meiosis 2.
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Aneuploidy
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Chromosome number is abnormal.
--Monosomy, Trisomy, Polyploidy |
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Monosomy
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Missing chromosome
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Trisomy
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Extra chromosome (Down Syndrome=trisomy 21)
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Polyploidy
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Extra sets of chromosomes.
--Common in plants. |
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Karyotype
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Photograph of chromosomes.
Analyzes shape, size, and number of chromosomes. |
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Autosomes
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Chromosomes other than the sex chromosomes (X, Y).
22 pairs in humans. |
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Genomic Imprinting
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The expression of a trait varies depending on which parent contributes the gene.
--E.g. Prader-Willi and Angelman Syndromes --2 different syndromes, both caused by the same mutation- deletion on chromosome 15. --Prader-Willi=paternal inheritance --Angelman=maternal inheritance |
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Fragile X Syndrome
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The most common cause of intellectual disability.
The tip of the "X" chromosome appears to hang by a thread. Caused by excessive tandem repeats within the chromosomes. |
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Extranuclear Inheritance
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Inheritance of genes found in mitochondria and chloroplasts.
Mitochondrial diseases--always inherited maternally. --Affect muscles and CNS- require lots of ATP. |
