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

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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

hybried

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

phenotype

appearance

genes

chemical makeup; types of genes

testcross

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

9:3:3:1

incomplete dominance

dominance that's characterized by blending

codominance

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

pleiotropy

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

epistasis

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.

polygenic

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

autosomes

44 chromosomes (1st 22 pairs) of the 46

sex chromosomes

2 chromosomes (23rd pair); X and Y OR X and X

sex-linked

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

carrier

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

crossover

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

recombination

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

pedigree

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

mutations

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

deletion

when a fragment lacking a centromere is lost during cell division

inversion

when a chromosomal fragment reattaches to its original chromosome but in the reverse orientation

translocation

when a fragment of a chromosome becomes attached to a nonhomologous chromosome

polyploidy

when a cell or organism has extra sets of chromosomes

nondisjunction

error that sometimes happens during meiosis in which homologous chromosomes fail to separate as they shouuld

aneuploidy

any abnormal number of chromosomes

trisomy

chromosome present is in triplicate

triploid

an organism with extra set of chromosome is called this; 3n

polyploid

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

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