Nondisjunction results in gametes that contain an

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•Nondisjunction results in gametes that •Contain an extra chromosome (n + 1) •Lack one chromosome (n −1) •Fertilization of an n + 1 gamete leads to trisomy •Fertilization of an n −1 gamete leads to monosomy •Cells with too many or too few of a chromosome are called aneuploid -------------------------------------------------------------------------------------------------------------------------------- TABLE 13.2 Crossing over contributes genetic variability between homologous chromosomes How many copies of chromosome 14 do your cheek cells contain 2 Where do the two copies of chromosome 14 in your cheek cells come from one from your mother and one from your father ( every cell in your body) Genetic Variation 13.2 Alleles, genotype and phenotype Genes for genetic characters occur in pairs One Gene inherited from each parent Alleles are different versions of gene The outward appearance of an individual is called their phenotype Phenotype: an individual’s observable characteristics (i.e., height, eye color etc.) Genotype: the genetic makeup of a cell or organism Genetic Variation Genetic variation describes naturally occurring genetic differences among individuals of the same species Variation permits flexibility and survival of a population in the face of changing environmental circumstances- natural selection. Meiosis and sexual reproduction enhances genetic variation Recombination is meiosis 1 prophase 1 Anaphase 1 two possible separation of ideals of homologs Genetic shuffling Sexual reproduction can introduce new gene combinations into a population This genetic shuffling is another important source of genetic variation Single nucleotide polymorphism Single Nucleotide Polymorphisms , frequently called SNP’s (snips) SNPs are scattered throughtout the genome and are found in both coding and noncoding regions SNPs can cause silent, harmless, harmful, or latent effects. Stable from generation to generation therefore useful as gene “markers” Why are SNPs Significant When SNPs occur withing a gene or in a regulatory region near a gene they may play a more direct role in disease by affecting the genes function Consequences of genetic variability There are many types of DNA and chromosomal variations in populations today Advanced sequencing techniques allow genetic variation to be studied directly in DNA molecules Different consequences for organisms Effects of Genetic Varation Can be: Harmless/Neutral No effect on organism e.g perception of bitter taste Often found in noncoding DNA The ability to taste PTC shows a dominant pattern of inheritance. A single copy of a tasting allele (T) conveys the ability to taste PTC. Non-tasters have two copies of a non-tasting allele (t)
Beneficial Patients were resistant to developing AIDS!!! CCR5 receptor mutation Harmful Can predispose to a disease or cause one Tumor suppressor genes such as p53 are genes whose loss of function through mutations may lead to cancer BRCA1 AND BRCA2 BRCA1 and BRCA2 are human genes that produce tumor suppressor proteins.

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