Unit 5 - Genetics
HOMOLOGOUS CHROMOSOMES are a pair of chromosomes having the same structural features. Each member of the pair of chromosomes has the same number and pattern of genes. The genes found in the same locus on both chromosomes carry information for the same character, but may have different alleles.
ALLELE (OR ALLELOMORPH): An allele is an alternative form that a gene can have due to successive mutations. They are found in the same locus in each homologous and carry information for the same character, e.g. the gene that determines straight hair and that which determines curly hair. A gene can have multiple alleles, but diploid organisms can only have two of those, as we have our chromosomes in pairs.
HOMOZYGOUS (TRUE-BREED): An organism which has a pair of identical alleles for a certain character is said to be homozygous for that character. Normally genes are represented by letters, so a homozygous organism will have the same letters (AA, aa, BB, etc)
HETEROZYGOUS (HYBRID): Organisms having different alleles for a character. E.g. Aa, Bb, etc.
COMPLETE DOMINANCE (DOMINANT HEREDITY): In all hybrid individuals an allele (the dominant allele) for a particular character, is fully expressed, and the other allele or recessive allele has no noticeable effect on the organisms appearance.
CODOMINACE: Neither allele is dominant or recessive. Instead both alleles are separately (equally) manifested in the phenotype. E.g. human blood type group AB.
INCOMPLETE DOMINANCE: It is characterized by an intermediate phenotype. For example the pink flowers of snapdragon hybrids.
GENOTYPE: It is the genetic information of a particular organism as specified by its alleles. The genotype is hereditary, as progenitors pass it down to their offspring, e.g. AaBb, etc.
PHENOTYPE: It is the observable characteristics of an organism produced by the interaction of its genes and the environment which surrounds its development. E.g. Black hair, blue eyes, etc. e.g. how the environment influences the phenotype of an individual: in the Himalayan rabbits, the genotype determines the presence of an enzyme which, at low temperatures, makes a dark pigment that affects certain body parts (nose, legs, tail etc) If the animal moves to a warmer place, the pigmentation in such places disappears.
ALLELE (OR ALLELOMORPH): An allele is an alternative form that a gene can have due to successive mutations. They are found in the same locus in each homologous and carry information for the same character, e.g. the gene that determines straight hair and that which determines curly hair. A gene can have multiple alleles, but diploid organisms can only have two of those, as we have our chromosomes in pairs.
HOMOZYGOUS (TRUE-BREED): An organism which has a pair of identical alleles for a certain character is said to be homozygous for that character. Normally genes are represented by letters, so a homozygous organism will have the same letters (AA, aa, BB, etc)
HETEROZYGOUS (HYBRID): Organisms having different alleles for a character. E.g. Aa, Bb, etc.
COMPLETE DOMINANCE (DOMINANT HEREDITY): In all hybrid individuals an allele (the dominant allele) for a particular character, is fully expressed, and the other allele or recessive allele has no noticeable effect on the organisms appearance.
CODOMINACE: Neither allele is dominant or recessive. Instead both alleles are separately (equally) manifested in the phenotype. E.g. human blood type group AB.
INCOMPLETE DOMINANCE: It is characterized by an intermediate phenotype. For example the pink flowers of snapdragon hybrids.
GENOTYPE: It is the genetic information of a particular organism as specified by its alleles. The genotype is hereditary, as progenitors pass it down to their offspring, e.g. AaBb, etc.
PHENOTYPE: It is the observable characteristics of an organism produced by the interaction of its genes and the environment which surrounds its development. E.g. Black hair, blue eyes, etc. e.g. how the environment influences the phenotype of an individual: in the Himalayan rabbits, the genotype determines the presence of an enzyme which, at low temperatures, makes a dark pigment that affects certain body parts (nose, legs, tail etc) If the animal moves to a warmer place, the pigmentation in such places disappears.