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Mendelian Genetics

Mendelian Genetics - homologous chromosomes separate at...

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Mendelian Genetics Through these meticulous experiments, Mendel came up with a 5-part hypothesis to explain the inheritance of single traits 1. Each trait is determined by pairs of genes; each organism has two alleles for each gene, one on each homologous chromosome Ex: white-flowered plants have different alleles than purple- flowered plants When two different alleles are present in an organism (heterozygous), a dominant allele may mask a recessive allele, even though the recessive allele is still present Ex: In edible peas the purple-flower trait is dominant to the white-flower trait (purple allele + white allele = purple flower) The pairs of alleles on homologous chromosomes separate, or segregate, from each other during meiosis , which is known as Mendel’s law of segregation (i.e. only one allele from the parent is passed on in a sperm or egg) Chance determines which allele is included in a given gamete—because
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Unformatted text preview: homologous chromosomes separate at random during meiosis Organisms have two copies of alleles for a given gene; some are homozygous for that gene (same alleles); some organisms are heterozygous for that gene (two different alleles) Punnett square: %perecent chance fr offspring Sex chromoshomes,sex-linked genes 5 realms of non mendelian genetics Abo blood groups Carriers, gentic disorders Nondisjunction The incorrect separation of chromosomes or in meiotic cell division is known as nondisjunction – Nondisjunction causes gametes to have too many and too few chromosomes – The frequency of nondisjunction increases with age – Most embryos that arise from fusion of gametes with abnormal chromosome numbers spontaneously abort, but some survive to birth – Nondisjunction in chromosomes 13, 18, 21, and sex chromosomes may survive to birth...
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