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1. DOMINANT
AND
RECESSIVE
TRAITS

2. DOM I NA NC E T R A I T S :
Dominance in genetics is a relationship between two alleles of a gene, in
which one allele masks the phenotype (the expression that we can see in the
outside) of another allele at the same genetics.

3. R E C E S S IV E T R A IT S :
A recessive trait is a trait caused by a recessive gene, which means
that someone must inherit two copies of the gene for the trait to
manifest.
When organisms such as humans reproduce, they produce young
with a genetic inheritance from both parents, caused by the fusing of
haploid sperm with haploid eggs to create a diploid organism.(In our
case we have 46 chromosomes, 23 comes from each parent), so
each chromosome contains a series of alleles or genes which code
various information.

5. E X P L A N A T IO N :
­When someone is heterozygous, however, one of the alleles will remain
inactive, and this allele represents a recessive trait.
­Gregor Mendel(considered the father od genetics beacuse of his experiments
on the fields)did much of his work with peas. In the course of his research, he
learned that purple was a dominant trait for flower color, meaning that a flower only
had to inherit one purple gene to produce purple flowers.
­When someone is heterozygous for a trait, the difference between dominant and
recessive traits becomes more important, because the dominant trait is the one
which will manifest.

6. F O R E XA M P L E :
When the alleles from both parents are the same(AA­AA), someone is said to
be homozygous at that allele. If a child inherits two different alleles, such as a
gene for red hair(RR) and a gene for brown hair(BB), he or she is said to be
heterozygous at that allele:
­When someone inherits the same allele twice,, that trait will manifest
whether or not it is dominant.
­When someone is heterozygous, however, one of the alleles will
remain inactive, and this allele represents a recessive trait.

8. E XA M P L E S
In the simplest case, where a gene exists in two allelic forms ( A and b),
three combinations of genotypes(alleles) are possible:
­AA: Homozygotic dominant.
­ Ab: Heterozygotic dominat.
­bb:HOmozygotic recessive.
­If AA and bb individuals (homozygotics) show different forms of the trait
(phenotype), and Ab individuals (heterozygotics) show the same phenotype
as AA individuals, then allele A is said to dominate or be dominant to or
show dominance to allele b, and b is said to be recessive to A.

9. E XA M P L E S :
1­The language of genetics consists of symbols and rules for using these symbols.When the
trait that we are studying is dominant we use a capital letter to show its symbol. When we
represent the recessive trait from the same trait we put the same letter but not capitalized.
EXAMPLE:
­If we have a tall pea plant dominat iver a short pea plant it will be represented like that:
Dominan(tall): T
Recessive(short): t
2­The following letters represent pairs of alleles.we have to indicate whether each pair is a
heterozygote(hybrid) or homozygote(purebrid).Later we can indicate whether each pair would
display a dominant or recessive phenotype
­DD:Homozygotic dominant ­Dd:Heterozygotic dominant
­ss:Hmozygotic recessive ­Rr: Heterozygotic dominant
­Tt:Heterozygotic dominant ­yy:Homozygotic recessive

10. S OURC ES :
I've got my information from these places:
http://www.wisegeek.com/what­is­a­recessive­trait.htm
http://en.wikipedia.org/wiki/Dominance_(genetics)
­My notebook and my own nowledge.