Biology- Gene Expression and Inheritance

Dihybrid Cross

A mating of a more complicated Punnett Square considers two allele pairs at locations on non-homologous chromosomes.

Dominant

Alleles requiring only one copy to be expressed. They are represented by a capital letter.

Recessive

Alleles that must have two copies present to be expressed. They are represented by lowercase letters.

Epistasis

An interaction between two independently inherited genes. Specifically, the phenotypic expression of one gene is dependent on the phenotypic expression of another gene at a different loci. The two genes sort independently. This type of inheritance pattern occurs to establish the color of Labrador retriever coats as black, brown (chocolate), or yellow. Two genes are involved: One (B/b) establishes the black and brown pigmentation (B allele= black; b allele=brown; B is completely dominant) and a second gene (E/e) determines whether the pigments will be deposited in the dog hairs (E allele=pigment deposited; e allele=pigment not deposited; E is completely dominant) The E/e gene is considered epistatic to the B/b gene because it ultimately determines whether the B/b gene will be expressed in the phenotype.

Codominance

As with complete and incomplete inheritance patterns, this occurs when a character is controlled by a gene with two alleles. In this case, if both alleles are present (heterozygoous state) both of the phenotypes they represent will also be present.

Three established inheritance patterns

Autosomal Dominant, Autosomal Recessive, and X-Linked (sex-linked) Recessive.

Autosomal Chromosomes

Carry genes other than those that determine sexual characteristics.

Sex Chromosomes

Carry the genes defining sexual characteristics as well as genes unrelated to sexual traits.

Homozygous Dominant

If two identical dominant alleles are present in a gene that has only two alleles...this arrangement is called this.

Homozygous Recessive

If two identical recessive alleles are present in a gene that has only two alleles....this arrangement is called this.

Multiple Alleles

In many genotypes for a character, there are more than just two alleles and this arrangement is called multiple allele inheritance.

Incomplete Dominance

In this inheritance pattern, there are two alleles, but neither is completely dominant over the other.

Heterozygous

Mixes of dominant and recessive alleles. The gene itself is referred to as gene A/a.

Complete Dominance

One of the alleles is always dominant and the other allele is always recessive. The type of pattern typically found in Mendelian genetics.

Rh

One of the blood groups found on RBCs in human blood. There are two alleles, R and r, with R completely dominant. R codes for a protein on the RBC surface, and the associated phenotype is called Rh+ or positive. The r allele does not code for any protein and therefore the homozygous recessive genotype is referred to as Rh- or negative. In the case of the Rh blood group, the trait referred to as expressed or not is the Rh- (negative) phenotype.

Monohybrid Cross

Only a single pair of alleles at one locus is considered.

Punnett Square

Possibility to predict probable genotypes and resulting phenotype ratios for progeny using a diagram called.....

Pedigree Charts

Reconstructions of the inheritance of a particular phenotype within several generations of a family. Once the phenotypes are established within the generations, genotypes and then the gene inheritance pattern can be determined. Studies of this represent similar inheritance patterns have revealed that they have common characteristics that can aide in identifying the patterns. Predictions of genotype and phenotype inheritance for individuals of future generations can then be made using Punnett squares. Genetic counselors can use this information to help prospective parents make difficult reproductive decisions if genetic diseases such as cystic fibrosis appear in the family pedigree.

Genes

Specific segments of the DNA molecule that control individual characteristics of organisms. Variant forms of genes are termed alleles.

Hemolytic Disease of the Newborn

The incompatibility can cause a disease in the newborn often termed HDN. (Rh is one blood group that must be matched when transfusing blood but is equally important to consider when Rh- women have babies that are Rh+) When the Rh+ blood of the fetus comes in contact with the Rh- blood of the mother, the mother's immune system will make antibodies that will attack and destroy the red blood cells of the fetus. With the first Rh+ child, the reaction is nonexistent or mild. However, the second and any subsequent Rh+ children this mother produces are exposed to antibodies already present in the mother's blood. This condition can cause anemia, jaundice, cerebral damage, mental retardation, and death in the child.

Sex-Linked Genes

The latter genes and are termed this because of their presence on the sex chromosomes.

Phenotype

The observable display of the expressed alleles is called the organism's ..........

Genotype

The term for the complete set of available genetic information in an individual. It can also refer to the alleles present for one particular gene.

Alleles

Variant forms of genes. Some genes have only two, many have more than two.