genetics Flashcards
allele
one alternative form of a given gene pair.
eg tall and short alleles for the height of pea plants.
allelic pairs
a combination of two alleles
genotype
the specific allelic combination for a certain gene or set of genes (Tt, TT, tt)
phenotype
the appearance of a trait in an individual ( what it looks like tall or short)
homozygous
an individual which contains two identical alleles ( DD, dd)
heterozygous
an induviual that contains two diffrent alleles for an allelic pair ( Dd)
testcross
the cross of any induviual to a homozygous recessive parent (to determine if the individual is homozygous dominant or heterozygous)
monohybrid cross
a cross between parents with different single allelic pair(AA x dd)
dihybrid cross
a cross between parents with different two allelic pairs (AaGg)
Mendelian traits
traits that exist in one of two forms; no intermediate forms (widow’s peak or straight line)
Continuous Traits
traits that exist in more than two forms; ( human height, skin colour, hair colour)
law of unit character
traits are inherited or passed on from generation to the next by genes and these genes occur in pairs.
law of dominance
one allele may mask the effect of the other.
law of segregation
during meiosis alleles separate one gamete carries one and the other carries the other one
law of independent assortment
two traits don’t depend on each other if a pea plant is yellow it doesn’t have to be round or wrinkled.
incomplete dominance
this occurs when both alleles are expressed resulting in a blending of the alleles
ex. Red snapdragons, X White snapdragons resulting in pink snap dragons.
codominance
this occurs when both alleles are expressed but not blended.
Ex. blood type AB in humans.
X-linked genes
this gene is located on the X chromosome.
multiple alleles
there are more than two possible alleles
Ex. four blood types
polygenic inheritance
sometimes two or more genes affect a single characteristic.
ex. skin pigment is controlled by 3 genes at least
sex-linked genes
a gene located on the sex chromosome is said to be sex-linked.
crossing over
crossing over the process in which the genetic information between two non-sister chromatids during prophase 1 of meiosis.
linkage map
a genetic map based on the frequency of recombination between genes due to crossing over
nondisjunction
during meiosis, there is an error that prevents the sister chromatids to separate properly resulting in one gamete having two copies of the same chromosome and the other gamete receiving no copy.
sex nondisjunction
nondisjunction of the sex chromosomes. when egg or sperm has an abnormal number of X or Y chromosomes.
eg Klinefelter’s XXY.
aneuploidy
the condition of possessing an abnormal chromosome number.
X-inactivation
in females, one of the x chromosomes becomes inactive forming a Barr body. females might have two types of cells.
Nonnuclear Inheritance
not all eukaryotic cell’s genes are located on nuclear chromosomes they are located on organelles. mitochondria and chloroplast contains DNA that carries a number of genes. for most plants and animals maternal inheritance is the rule for mitochondrial genes. most of the mitochondria is passed to the zygote from the cytoplasm of the egg the spem only contributes a haploid set of chromosomes. the egg also contributes that but it also contributes the cytoplasm and organelles. the genes of the mitochondria code for enzzymes that are involved in making ATP. ATP synthatse enzymes , protien complexes of the electron transport chain. mutations in mitochondrial dna reduce the amount of ATP and causees rare human disorders.
