Biology Quiz: Chapter 7

Gregor Mendel

A monk living in what is now the Czech Republic in the mid-1800s, was the founder of the modern science of genetics (1) T.B. He understood the essence of the genetics puzzle and pieced it all together.

Codominance

A single gene controls ABO blood type system with three alleles. Two of the alleles are dominant ("IA or A" for Blood Type A, "IB or B" for Blood Type B) and the third allele ("i or O" for Blood Type O) is recessive. The gene encodes an enzyme glycosyltransferase that modifies carbohydrates that make up the red blood cell antigens. Since there are two of the dominant alleles, IAIB genotype expresses codominance for Type AB blood. The three genotypes result in four phenotypes, A, B, AB, and O. (3) T.B.

Alleles

Alternate forms of a gene.

Heterozygous

An individual who inherits a different allele from each parent.

Genotype

An organism's genetic composition.

Pedigrees

Help scientists, doctors, animal and plant breeders, and prospective parents determine the genes that individuals carry and the genes that their offspring will likely carry.

Mendel's law of segregation

Of the two copies of each gene everyone carries, only one of the two alleles gets put into each gamete is significant.

Mendel's law of independent assortment

States that the alleles of one gene sort into gametes independently of the alleles of another gene (5) T.B. Also, all traits are inherited independently of each other.

Incomplete dominance

The heterozygote appears to be intermediate between the two homozygotes.

Codominance

The heterozygote displays characteristics of both homozygotes.

Sex-Linked Inheritance

The normal female condition is a result of the chromosomal pairing XX, while the normal male condition is XY. Certain genes located on the X chromosome, not associated with female sex characteristics, cause sex-linked recessive traits. As a result, females must receive two recessive alleles to exhibit any particular characteristic associated with one of these genes, while males need only receive one allele. The reason for the male anomaly is that the Y chromosome does not carry versions of the same genes as the X chromosome. Consequently, only females can be true heterozygotes (one dominant allele and one recessive allele). In humans colorblindness (b) is an example of a sex-linked recessive trait. In this problem, a male with colorblindness marries a female who is not colorblind but carries the (b) allele. Using a Punnett square, determine the genotypic and phenotypic probabilities for their potential offspring. (4) T.B.

Phenotype

The outward appearance of an individual.

Heredity

The passing of characteristics from parent to offspring through their genes.

Sex-linked traits

Traits that are controlled by genes on the sex chromosomes.

Single-gene traits

Traits that are determined by the instructions a person carries at one gene. A dominant trait masks the effect of a recessive trait when the individual carries both the dominant and the recessive versions of the instructions for the trait.

Homozygous

When an individual inherits two copies of the same allele, it shows the trait specified by the instructions embodied in those alleles.