8.1 Genetic information
- Created by: phoebeschofield02
- Created on: 03-01-19 13:58
Origins of genetic variation
-Meiosis as a source of genetic variation -->
- independent (random) assortment= the components of the chromosome pairs are distributed randomly , so any number from 0 to 23 chromosomes in your gametes can come from the paternal or maternal chromosomes
- crossing over (recombination)= during meiosis, large multi-enzyme complexes cut and join bits of the maternal and paternal chromatids together at the chiasmata, this exchange of genetic material leads to increased genetic variation
-there are three types of mutation -->
- point/gene mutations= miscopying of one/a small number of nucleotides. Inc substitution, deletions, insertions etc
- chromosomal mutaions= changes in the positions of genes w/in the chromosomes. More likely to show a measurable change in the organism
- chromosome mutations= when an entire chromosome is lost during meiosis or dupliacted in one of the cells due to an error
-random fertilisation as a source of mutation -->
- when the gametes of 2 unrelated individuals fuse, this creates genetic variation
- the combination of female and male gametes is random
-the physical and chemical characteristics that make up an organism are known as the phentoype
-the genotype is the genetic information
-the phenotype is partly the result of the genotype and partly the result of an organism's environment
-each gene on a chromosome is a different segment of DNA, coding for a particular protein or polypeptide
-the chromosomes in a homologous pair carry the same genes, except for the sex chromosomes
-the gene for a particular characterisitic is always found in the same position (locus)
-each gene exists in slightly different versions, called alleles
-if both alleles for a particular characteristic are identical then the individual for is homozygous for that characteristic
-if the two alleles for a particular characteristic are different, then the individual is heterozygous for that characterisitic
-polygenic= traits determined by several interacting genes
-homozygotes are referred to as true breeding as becuase if you cross two homozygotes for breeding,all of the resulting offspring will b ehomozygous for that trait
-when one gene at a time is considered in a genetic cross, it is called a monogenic cross
-the first generation on a mongenic cross (punnet square) is called F1 (fillial one)
-a test cross is sometime used to reveal the parental genotype
-Mendel:
- discovered the ratio for when looking @ more than one gene at a time
- 9:3:3:1
- law of segregation= one allele for each trait is inherited from each parent, giving a total of two alleles for each trait. The segregation in each allele takes place when the gametes are formed
- law of independent assortment= different traits are inherited independently of each other
- some traits havr multiple alleles --> there are more that 2 possible…
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