Chapter 8 Flashcards
character
an observable physical feature
trait
a particular form of a character
parental generation
designated by the letter P
first filial generation
designated by F1, these plants are the offspring of the P generation
monohybrid cross
crossing paternal varieties with contrasting traits for a single character
alleles
the different forms of a gene
dominant
determines the phenotype for heterozygous and homozygous dominant
recessive
determines the phenotype for homozygous recessive only
homozygous
has two alleles that are the same
heterozygous
has two different alleles
phenotype
physical appearance of an organism
genotype
genetic constitution of the organism
law of segregation
when any individual produces gametes, the two copies of a gene separate, so each gamete receives only one copy
Punnett square
method that ensures we consider all possible random combinations of gametes when calculating expected genotype frequencies
test cross
used to determine whether an individual showing a dominant trait is homozygous or heterozygous
dihybrid cross
cross between individuals that are identical double heterozygotes
dihybrid cross phenotype ratio
9:3:3:1
multiplication rule
the probability of two independent outcomes occurring together is found by multiplying the two individual probabilities
addition rule
the probability of an event that can occur in two or more different ways is the sum of the individual probabilities of those ways
pedigrees
family trees that show the occurrence of inherited phenotypes in several generations of related individuals
mutations
rare, stable, and inherited changes in the genetic material
wild type
the allele that is present in most individuals in nature
polymorphic
a gene with a wild-type allele that is present less than 99 percent of the time
incomplete dominance
heterozygotes have an intermediate phenotype
codominance
when two alleles of a gene both produce their phenotypes when present in a heterozygote
epistasis
occurs when the phenotypic expression of one gene is affected by another gene
heterosis
hybrid vigor, when genes interact in a dramatic way
What is the general relationship between phenotypes and genes?
most complex phenotypes are determined by multiple genes
quantitative traits
traits conferred by multiple genes that need to be measured rather than assessed qualitatively
How is the phenotype of an organism truly determined?
by both genotype and environment
penetrance
the proportion of individuals in a group with a given genotype that actually show the expected phenotype
expressivity
the degree to which a genotype is expressed in an individual
heritability
the relative contribution of genetic versus environmental factors to the variation in that character in a particular population (typically varies from 0 to 1)
locus
the particular site on a chromosome where a gene resides
The ________ of genes on a single chromosome alters their pattern of inheritance
genetic linkage
recombinant
two homologous chromosomes can physically exchange corresponding segments during prophase I of meiosis by crossing over
recombination frequency
calculated by dividing the number of recombinant progeny by the total number of progeny
autosomes
all the chromosomes that aren’t sex chromosomes
sex chromosomes
determine the sex of the fly
hemizygous
any gene that is present as a single copy in a diploid organism
sex-linked inheritance
inheritance of a gene that is carried on a sex chromosome
What organelles contain genetic material?
nucleus, mitochondria and plastids
How many genes are there in the nuclear genome for humans?
21,000
How many genes are there in the mitochondrial genome for humans?
37
In most organisms, the mitochondria and plastids are inherited only from the ______.
mother
horizontal/lateral gene transfer
the transfer of genes from one individual organism to another without sexual reproduction
sex pilius
extends from one cell to another cell and draws them together
conjugation tube
a thin cytoplasmic bridge that allows genetic material to pass from the donor to the recipient
bacterial conjugation
the process where the donor transfers genetic material to the recipient (not the other way around)
What happens when the donor DNA is inside the recipient cell?
it can recombine with the recipients DNA
plasmids
smaller, circular DNA molecules in bacteria that replicate independently inside the cell
How do plasmids replicate?
independently of the main chromosome
Do plasmids need to recombine with the main chromosome to add their genes to the recipient cell’s genome?
no
Plasmids can move between cells during ______, thereby transferring new genes to the recipient bacterium.
conjugation
