Genetics Vocabulary Allele — alternative forms of a gene for each variation of a trait of an organism Crossing over — exchange of genetic material between non-sister chromatids from homologous chromosome during prophase I of meiosis; results in new allele combinations Diploid — cell with two of each kind of chromosome; is said to contain a diploid, or 2n, number of chromosomes Dominant — observed trait of an organism that mask the recessive form of a trait Egg — haploid female sex cell produced by meiosis Fertilization — fusion of male and female gametes Gamete — male and female sex cells, sperm and eggs Genetic recombination — major source of genetic variation among organisms caused by re-assortment or crossing over during meiosis Genetics — branch of biology that studies heredity Genotype — combination of genes in an organism Haploid — cell with one of each kind of chromosome; is said to contain a haploid or n, number of chromosomes. Heredity — passing on of characteristics from parents to offspring Heterozygous — when there are two different alleles for a trait Homologous chromosome — paired chromosomes with genes fro the same traits arranged in the same order. Homozygous — when there are two identical alleles for a trait Hybrid — offspring formed by parents having different forms of a specific trait. Law of independent assortment — Mendelian principal stating that genes for different traits are inherited independently of each other. Law of segregation — Mendelian principal explaining that because each plant has two different alleles, it can produce two different types of gametes. Nondisjunction — failure of homologous chromosomes to separate properly during meiosis; results in gametes with too many or too few chromosomes Phenotype — outward appearance of an organism, regardless of its genes.
Gregor Mendel, through his work on pea plants, discovered the fundamental laws of inheritance. He deduced that genes come in pairs and are inherited as distinct units, one from each parent. Mendel tracked the segregation of parental genes and their appearance in the offspring as dominant or recessive traits. He recognized the mathematical patterns of inheritance from one generation to the next.
Genetic information from an ,year-old human fossil has been retrieved for the first time. The results from the University of Copenhagen shed light on one of the branching points in the human family tree, reaching much further back in time than previously possible. An important advancement in human evolution studies has been achieved after scientists retrieved the oldest human genetic data set from an ,year-old tooth belonging to the hominin species Homo antecessor. Our results support the idea that Homo antecessor was a sister group to the group containing Homo sapiens , Neanderthals, and Denisovans," says Frido Welker, Postdoctoral Research Fellow at the Globe Institute, University of Copenhagen, and first author on the paper.
Mendel proposed that paired unit factors of heredity were transmitted faithfully from generation to generation by the dissociation and reassociation of paired factors during gametogenesis and fertilization, respectively. After he crossed peas with contrasting traits and found that the recessive trait resurfaced in the F 2 generation, Mendel deduced that hereditary factors must be inherited as discrete units. This finding contradicted the belief at that time that parental traits were blended in the offspring.