Bio Vocab Chapter 9

Alleles

An alternative version of a gene.

Carrier

An individual who is heterozygous for a recessively inherited disorder and who therefore does not show symptoms of that disorder but who may pass on the recessive allele to offspring.

Character

A heritable feature that varies among individuals within a population, such as flower color in pea plants or eye color in humans.

Codominance

Inheritance pattern in which a heterozygote expresses the distinct trait of both alleles.

Complete Codominance

A type of inheritance in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable.

Cross

A mating of two sexually reproducing individuals; often used to describe a genetics experiment involving a controlled mating (a “genetic cross”).

Cross Fertilization

Fertilization of one plant by pollen from a different plant.

Dihybrid Cross

An experimental mating of individuals that are each heterozygous for both of two characters (or the self-pollination of a plant that is heterozygous for both characters).

Dominant Allele

The allele that determines the phenotype of a gene when the individual is heterozygous for that gene.

F1 Generation

The offspring of two parental (P generation) individuals; F1 stands for first filial.

F2 Generation

The offspring of the F1 generation; F2 stands for second filial.

Genetics

The scientific study of heredity. Modern genetics began with the work of Gregor Mendel in the 19th century.

Genotype

The genetic makeup of an organism.

Gregor Mendel

The man who deduced the fundamental principles of genetics by breeding garden peas.

Hemophilia

A rare disorder in which the blood doesn't clot in the typical way because it doesn't have enough blood-clotting proteins

Heterozygous

Having two different alleles for a given gene.

Homozygous

Having two identical alleles for a given gene.

Hybrid

Offspring that results from the mating of individuals from two different species or from two true-breeding varieties of the same species; an offspring of two parents that differ in one or more inherited traits; an individual that is heterozygous for one or more pairs of genes.

Incomplete Dominance

A type of inheritance in which the pheno-type of a heterozygote (*Aa*) is intermediate between the phenotypes of the two types of homozygotes (*AA* and *aa*).

Law Of Independent Assortment

A general rule of inheritance (originally formulated by Gregor Mendel) that when gametes form during meiosis, each pair of alleles for a particular character segregates independently of other pairs; also known as Mendel’s second law of inheritance.

Law Of Segregation

A general rule in inheritance (originally formulated by Gregor Mendel) that individuals have two alleles for each gene and that when gametes form by meiosis, the two alleles separate, each resulting gamete ending up with only one allele of each gene; also known as Mendel’s first law of inheritance.

Monohybrid Cross

An experimental mating of individuals that are heterozygous for the character being followed (or the self-pollination of a heterozygous plant).

P Generation

The parent individuals from which offspring are derived in studies of inheritance; P stands for parental.

Pedigree

A family genetic tree representing the occurrence of heritable traits in parents and offspring across a number of generations. A _______ can be used to determine genotypes of matings that have already occurred.

Phenotype

The expressed traits of an organism.

Punnett Square

A diagram used in the study of inheritance to show the results of random fertilization.

Recessive Allele

An allele that has no noticeable effect on the pheno-type of a gene when the individual is heterozygous for that gene.

Self-Fertilization

Fusion of male and female gametes (sex cells) produced by the same individual.

Sex-Linked Gene

A gene located on a sex chromosome. In humans, the vast majority of ________ genes are located on the X chromosome.

Testcross

The mating between an individual of unknown genotype for a particular character and an individual that is homozygous recessive for that same character. The ________ can be used to determine the unknown genotype (homozygous dominant versus heterozygous).

Trait

A variant of a character found within a population, such as purple or white flowers in pea plants.

True-Breeding

Referring to organisms for which sexual reproduction produces offspring with inherited traits identical to those of the parents. The organisms are homozygous for the characters under consideration.