4.2 Flashcards
law of separation
the two copies of a gene separate during gamete formation
each gamete contains one copy (allele) of a gene
meiosis
explains the principle of segregation
alleles of a gene segregate as chromosomes separate during meiosis I
each gamete contains one copy of each gene
sister chromatids
refers to the identical copies formed by the DNA replication of a chromosome
punnett square
can be used to predict the genotypic and phenotypic ratios in the offspring from a cross
PP - P | P (meiotic segregation)
3:1 ratio (F2 generation) explained by all four combinations in the punnet square being equally likely, which is equal segregation
test cross
used to determine whether an individual with a dominant phenotype is homozygous or heterozygous
individual with dominant phenotype is crossed with a homozygous recessive individual
probability
used to predict inheritance
one key to Mendel’s success was large sample size
by counting many progeny, he was able to see clear patterns
geneticists began using probability calculations and statistical techniques
probability numbers
chance that a certain event will occur
event is certain to happen = 1
event cannot possibly happen = 0
all other events have a probability between 0 and 1
multiplication rule
the probability of two or more independent events happening together is the product of their independent probabilities
probability of two independent events (A and B) happening = Pa x Pb
addition rule
probability of an event that can occur in two or more different ways is the sum of the individual probabilities
the probability of an event (A or B) that can occur in two different ways = Pa + Pb
pedigrees
diagrams that show the phenotypes and/or genotypes for a particular organism and its ancestors
used to analyze human crosses that already exist
genetic relationships, person’s sex, phenotypes
mode of transmission
pedigrees can be used to determine the mode of transmission of a trait
if a given trait is due to a single gene, the pedigree reveals whether
-the trait is autosomal or sex-linked
-the trait is due to a dominant or recessive allele
rare recessive alleles
affected people can have two parents who are not affected
only a small proportion of people affected
unaffected parents of an affected individual are heterozygous carriers for the trait
carriers have the allele and transmit it without exhibiting the phenotype
albinism
rare dominant alleles
expressed in any individual with at least one dominant allele
individual homozygous or heterozygous for the trait with display the dominant phenotype
every affected person has an affected parent
about half the offspring of an affected parent are also affected
Huntingdon’s Disease
