Cheatography
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Basics of Heredity and Mendelian Genetics
This is a draft cheat sheet. It is a work in progress and is not finished yet.
Genetic Diversity
Meiosis I:
-Separation of the homologous chromosomes allows each gamete to receive haploid (1n) set of chromosomes (both maternal and paternal chromosomes)
-Homologous chromatids exchange genetic material via “crossing over” (recombination)
a. Increases genetic diversity among the resultant gametes
Increase Variation:
-Sexual reproduction
a. Crossing over, random assortment of chromosomes during meiosis, and subsequent fertilization of gametes |
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Non-Mendelian Genetics
Phenotypic ratios differ from predicted ratios |
Linked genes |
Genes on the same chromosome |
Recombination frequency |
(# of recombinants/total # in population) x 100 = () LMU |
Multiple alleles |
More than 2 alleles present in a population (IA, IB, i) |
Incomplete dominance |
Traits "blended"; neither dominant |
Co-dominance |
Both traits displayed (spots, strippes etc.) |
Sex-Linked |
X or Y linked traits |
Barr Body |
Inactivated X chromosome in each female mammal's somatic cell |
Non-nuclear |
Chloroplasts and mitochondria are randomly assorted to gametes and daughter cells (both maternally inherited in plants and animals) |
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Laws of Mendelian Genetics
Law of Dominance: when inherited heterozygous, the allele expressed is dominant and the allele not expressed in recessive |
Law of Segregation: (1) The two alleles for each trait segregate, during the formation of gametes (2) During formation of new zygotes, the alleles will combine at random with other alleles |
Law of Independent Assortment: different genes and their alleles are inherited independently |
Types of Crosses
Monohybrid |
Ll x Ll; phenotype ratio=3:1; genotype ratio=1:2:1 |
Dihybrid |
LlPp x LlPp; 4 types of gametes; phenotype ratio = 9:3:3:1 |
Test Cross |
T_x tt to determine unknown genotype |
Polygenetic Traits
Blending of multiple genes, identified by bell curve distribution
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