Ch. 14 Mendel and the Gene Idea and 15 Chromosomal Basis of Inheritance

Gregor Mendel
bred garden peas in order to study patterns of inheritance
particulate inheritance
type of inheritance where inherited characteristics are carried by discrete units known as genes
multiplication rule
for finding probability of two independent events happening, multiply chance of one happening by the chance that the other will happen
addition rule
for finding when more than one arrangement of events producing the specified outcome is possible, the probabilities for each outcome are added together
law of dominance
when 2 organisms, each homozygous for two opposing traits are crossed the offspring will be hybrid but will exhibit only the dominant trait
carrying 2 different alleles
law of segregation
states that during the formation of gametes, the 2 traits carried by each parent will separate
Monohybrid cross
Tt x Tt is this type of cross; cross of 2 organisms each hybrid for one trait
chemical makeup; types of genes
way to determine the genotype of an individual plant or animal showing the dominant trait; individual bring tested is crossed with homozygous dominant
law of independent assortment
applies when a cross is carried out between 2 individuals hybrid for 2 or more traits that are not on the same chromosome; the only factor that determines how these alleles segregate or assort is how the homologous pairs line up in metaphase of meiosis I
dihybrid cross
cross between individuals hybrid for 2 or more traits not on the same chromosome
linked genes
genes that are on the same chromosome; they won't assort independently
phenotype ratio of a dihybrid cross
incomplete dominance
dominance that's characterized by blending
dominance where both traits show because there is a single gene locus at which 2 allelic variants are possible, making it so the hybrid is NOT an intermediate of the 2 phenotypes; such as blood groups in humans (A, B, AB, O)
multiple alleles
more than 2 forms of allelic forms of a gene
ability of a single gene to affect an organism in several or many ways; ex: in siamese cats, an allele responsible for coloration pattern is responsible for cross-eyed trait
2 separate genes control 1 trait, but 1 gene masks the expression of the other gene. the gene that masks the expression of the other gene is epistatic to the gene it masks. ex: melanin production has 2 alleles, C, which produces pigment, and c, which doesn't. if C isn't there to make melanin in the first place, even if a 2nd gene codes for melanin deposition, none will deposit because C isn't there.
many characteristics like skin, hair color, and height come from a blending of several separate genes that vary along a continuum.
nurture vs. nature
interaction of genetic predisposition and the environment
sex-influenced trait
inheritance influenced by the sex of he individual carrying the traits; NOT sex-linked necessarily
# of linkage groups
is equal to the number of chromosomes; humans have 46
44 chromosomes (1st 22 pairs) of the 46
sex chromosomes
2 chromosomes (23rd pair); X and Y OR X and X
traits carried on the X chromosome (Y is too short); females inherit 2 copies of these genes; males inherit 1 of these genes on their one X
recessive mutation
females only express this mutation if they have 2 mutated genes
carries one of each gene; males can't be this for sex-linked genes
dominant mutation
females can express this mutation if they have only 1 of this mutated gene
sex-linked examples
color blindness, hemophilia, muscular distrophy
the farther apart genes are on a chromosome, the more likely they'll be separated from each other during meiosis due to this event occuring at the chiasmata. makes it so AB x ab has 4 types of gametes(AB, Ab, aB, ab) instead of 2(AB, ab). is a major source of variation in sexually producing organisms
the result of crossing over; is a major source of variation in sexually producing organisms
map unit
distance on a chromosome that is the distance within which recombination occurs 1% of the time; rate of crossover doesn't give actual distance, but can give order of linked genes on the chromosome
linkage map
maps the differences between genes that are linked
family tree that indicates the phenotype of one trait being studied for every member of the family; used to find how particular trait is inherited
x inactivation
early in the development of the embryo of a female mammal, one of the 2 chromosomes is inactivated in every somatic cell
genetic mosaic
produced by x inactivation in female mammals because sometimes one x is inactivated, sometimes the other is inactivated
barr body
the dark spot on the chromatin of every somatic cell in a female that is produced due to x inactivation
changes in the genome; there are chromosome types and gene types
genetic disorders
PKU, cystic fibrosis, tay-sachs huntington's disease, hemophilia, color blindness, duchenne muscular distrophy, sickle cell
chromosomal disorders
down syndrome, turner's syndrome, klinefelter's syndrome
when a fragment lacking a centromere is lost during cell division
when a chromosomal fragment reattaches to its original chromosome but in the reverse orientation
when a fragment of a chromosome becomes attached to a nonhomologous chromosome
when a cell or organism has extra sets of chromosomes
error that sometimes happens during meiosis in which homologous chromosomes fail to separate as they shouuld
any abnormal number of chromosomes
chromosome present is in triplicate
an organism with extra set of chromosome is called this; 3n
organism with extra sets of chromosomes
extranuclear genes
genes found in the mitochondria and chloroplasts; defects in the DNA here affects amount of ATP made and therefore the nervous system and muscles; always inherited from the mother