Genetics is the science of inheritance from one generation down to the next.
Genes are passed from the adult cells to the forming zygote. A gene is a length of DNA that determines a particular characteristic of an organism. A gene can be pinpointed to a specific location called the loci on the chromosome. Not all genes can be pinpointed to a specific loci, for example your height is determined by several genes.
The human genome is split into 23 chromosomes. But each cell has copies of each cell, one from the mother and one from the father giving the offspring 46 chromosomes. Alleles are different versions of a gene. Because the 23 chromosomes comes from each parent, the offspring would have two different copies of a chromosome and more specific, two different genes (alleles). It is because the offspring has two different alleles, it is able to have genetic variation.
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| As you can see there are a total of 46 chromosomes, 23 from the mother and 23 from the father. |
GENOTYPE
Genotype is the genetic makeup of the organism, the DNA sequence.
Heterozygote is when an organism has two DIFFEERENT alleles at a loci.
Homozgote is when the organism have two of the same alleles at a loci.
PHENOTYPE
-Phenotype is the physical expression hat is given from a gene.
-When the individual is in a heterozygote stage and one allele is expressed it is call the dominant allele. The allele that is not expressed it is called a recessive allele.
-An upper case letter (A) stand for dominant and lower case letter (a) stands for recessive.
-Sometimes there is a mix of both alleles, it is called Incomplete Dominance. An example of this would be a flower that has the red allele R and white allele W. You will get RW which will give the flower a mixture of both red and white, pink. In Incomplete Dominance a blend of the alleles is expressed.
-Codominance is when both alleles are expressed. and example of this would be with blood. Type A, B and O stand for the antigen present on the surface of the red blood cell. The three alleles are IA
IB and i. IA and IB are codominant so they will cause the red blood cell the express both antigen NOT a mixture of them.
The rhesus factor is another antigen used for blood typing. A cell is Rh positive having the alleles of RhD RhD or RhD Rhd and it can be negative by having Rhd Rhd.
