bio topic 3/10 definitions

gene

gene

a heritable sequence of nucleotides on DNA molecules that code for an amino acid sequence for a specific polypeptide

chromosome

sections of DNA that contain over a thousand genes and other associated DNA

homologous chromosomes

chromosomes with the same centromere position, length, staining pattern, gene loci, with different alleles

bivalent

a pair of homologous chromosomes bound together by invisible protein structures

locus

specific position that a gene occupies on the chromosome

allele

specific form of a gene that gives rise to variation

genome

the entire set of genetic material in an organism, including mitochondria and chloroplast DNA

plasmid

small extra DNA molecules found in prokaryotes, trans-species

karyotype

the number and type of chromosomes in a cell

karyogram

photograph of all chromosomes in a cell obtained by bursting it during metaphase

genotype

a pair of alleles possessed by an organism

homozygous

when identical alleles constitute the genotype

heterozygous

when different alleles constitute the genotype

dominant allele

allele that has the same effect on the phenotype when in heterozygous and homozygous state

recessive allele

allele that only influences the phenotype in the homozygous state

codominant allele

a pair of different alleles that both affect the phenotype when they are in the heterozygous state, causing continuous variation

test cross

crossing with a homozygous recessive organism to determine if the organism is heterozygous

if heterozygous, will produce 1:1:1:1 genotype ratio

linkage group

a group of genes whose loci are on the same chromosome and do not independently assort, tending to be inherited together

recombinants

combinations of linked genes not found in parents due to crossing over, producing offspring with a different phenotypem

monogenic traits

characteristics controlled by a single gene locus

polygenic traits

characteristics controlled by two or more gene loci, and tend to display continuous variation, with each gene having an additive effect

cystic fibrosis

autosomal recessive disease

huntington’s

autosomal dominant disease

haemophilia

sex-linked recessive disease

colour blindness

sex-linked recessive disease

sickle cell anemia

base substitution: GAG → GTG (sense strand) and GUG (mRNA)

codominant allele, with homozygous form being lethal and the heterozygous form being a carrier with malaria resistance

mendel’s law of independent assortment

the separation of one pair of alleles between the daughter cells is independent of the separation of another pair of alleles, caused by random orientation

exception to law: linked genes

mendel’s law of segregation

gametes each receive a single copy of one of the alleles of a gene

exception to law: nondisjunction

mendel’s principle of dominance

recessive allele will be masked by dominant alleles

exception to law: codominant alleles