Review of Human Traits GENETICS LEC 2GTaghavi Komsari Esmaeil Yusuf A.Meer
Review of Human TraitsAnalyses of human traits offer genetic examples including dominance, incomplete dominance, co-dominance, and sex linkage and … What are Alleles?Alleles are variations of a gene. A diploid organism gets one set of their alleles (genes) from one parent and the other set of alleles from the other parent. Definition of genetic trait : A physical characteristic brought about by the expression of a gene or manygenes. Examples of traits are height, eye color, and the ability to roll your tongue. Variations in these characteristics are dependent upon the particular alleles an individual has for the genes determining the trait. RRR
dominant traitIn genetics, a trait that will appear in the offspring if one of theparents contributes it. (Compare recessive trait.)In humans, dark hair is a dominant trait; if one parentcontributes a gene for dark hair and the other contributes agene for light hair, the child will have dark hair. ,
recessive traitIn genetics, a trait that must be contributed by both parents inorder to appear in the offspring. Recessive traits can be carried ina persons genes without appearing in that person or In genetics, the term"recessive gene" refers to an allele that causes a phenotype (visible or detectablecharacteristic) that is only seen in a homozygous genotype (an organism that hastwo copies of the same allele) and never in a heterozygous genotype.Attached earlobes were previously believed to be a recessive phenotype.
Co dominant TraitsA number of human traits are the result of 2 types of alleles thatare equally dominant. Such traits are said to be co dominant for thattrait. When an individual is heterozygous for such traits, the resultingphenotype or expression of these two traits is a blending, because bothtraits are expressed equally.Example: blood grouping. IA, and the B allele, properly designated as IB) are codominant .
Incomplete DominanceIncomplete dominance is a form of intermediate inheritance inwhich one allele for a specific trait is not completely dominantover the other allele. This results in a combined phenotype.The most well-studied example of incomplete dominance in humans occurs in thegenes for curly hair.
.Sex-linked trait :.A trait genetically determined by an allele located on the sex chromosome .. Sex-linked traits are most commonly found on the X chromosome and includecolor blindness (both red and green types), hemophilia (types A and B), icthyosis(a skin disorder causing large dark scales), and Duchenne muscular dystrophy.There are very few Y-linked traits. Hairy ears, a relatively rare trait, is a Y-linkedtrait..
X-linked traitAny trait or characteristic whose appearance or absence in a person isdetermined by a gene on the sex chromosomes. Typically, these genesare found on the X chromosome but not on the Y chromosome.Example: Diabetes.
Y- linked traitY-linked traits are traits whose allele is carriedon the Y chromosome . Most Y linkedmutations lead to sterility , and can not beinherited.Example:Hypertrichosis.
Sex influenced.sex-influenced traits are those that are expressed differently in thetwo sexes. Such traits are autosomal, which means that the genesresponsible for their expression are not carried on the sexchromosomes. An example of a sex-influenced trait is male-patternbaldness.The baldness allele, which causes hair loss, is influenced by thehormones testosterone and dihydrotestosterone, but only whenlevels of the two hormones are high. In general, males have muchhigher levels of these hormones than females, so the baldnessallele has a stronger effect in males than in females..
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