Chapter 7 Genotypes and phenotypes | Biology for Units 1&2

genotype

the combination of alleles for a gene

phenotype

the physical expression of the genotype and its environment

homozygous

a genotype in which the two alleles for the gene are the same

heterozygous

a genotype in which the two alleles for the gene are different

dominant trait

the trait that is expressed in the phenotype of a heterozygous individual

recessive trait

the trait that is only expressed in the phenotype of a homozygous individual

carrier

a heterozygous individual with one allele for the recessive trait but who shows the dominant trait

hemizygous

a genotype in which thre is only one copy of the gene

dominance

refers to the relationship between the alleles of a gene and the observable phenotype

complete dominance

a pattern of dominance in which the recessive trait is completely masked by the dominant trait in a heterozygous genotype

dominant phenotype

the phenotype that is seen in a homozygous individual and a heterozygous individual

recessive phenotype

the phenotype that is observed from a homozygous recessive genotype

codominance

a pattern of dominance in which two traits are equally dominant and the heterozygous individual displays both traits

incomplete dominance

a pattern of dominance in which a heterozygous individual displays an intermediate phenotype that is a combination of the two alleles

polygenic trait

a trait controlled by multiple genes

phenylketonuria (PKU)

a genetic disorder that causes a build-up of phenylalanine, which can lead to problems with brain development

epigenetics

the study of changes in gene expression caused by modification of the DNA without changing the sequence

DNA methylation

the process of adding methyl groups to the cytosine bases of DNA, which can change the expression of a gene

histone modification

the addition of chemical groups to histone proteins, which affects the spacing between nucleosomes and therefore gene expression

epigenome

the epigenetic modifications to the DNA and histone proteins of an individual