bio heredity

alleles

alternative forms of the same genes

crossing over

the exchange of two homologous chromosomes of like parts, breaks linkage groups; site is called a chiasma

first filial generation (F1)

the immediate heterozygous progeny of a parental mating

genotype

the genetic make-up

heterozygous

having two different alleles for the same trait; hybrid

homologous chromosomes

a pair of identical chromosomes

homozygous

having two of the same alleles; pure

homozygous recessive

the genotype of a recessive trait

hybrid

Offspring of crosses between parents with different traits; heterozygous

intermediate inheritance

incomplete dominance

linkage group

genes that are linked on the same chromosome, linked loci, do not assort independently, humans have 46

locus (plural: loci)

a site on a chromosome where a gene for a particular trait is located

parental generation (P1)

The first generation of parents. Both are true-breeding.

phenotype

the expression of genes

pleiotropy

ability of a single gene to affect many characteristics. ex: frizzle trait for chickens (malformed feathers); coloration pattern in Siamese cats; Marfan syndrome for humans

second filial generation (F2)

the result of crossing hybrids

testcross

a cross between an organism with a dominant phenotype and one with a homozygous recessive

karyotype

a chart that organizes chromosomes in relation to number, size and type

nondisjunction

improper separation of chromosomes during meiosis

"blending" hypothesis

genes contributed by two parents are mixed

monohybrid cross

cross that involves a single character in which both parents are heterozygous (Tt x Tt), yields 1:2:1 genotypic ratio and 25:75 recessive to dominant phenotypic ratio

law of segregation

every organisms carries pairs of alleles for each trait that separate during the formation of gametes

law of independent assortment

members of each pair of factors are distributed independently when the gametes are formed

law of dominance

when two opposite pure-breeding varieties of an organism are crossed, all offspring resemble one parent

incomplete dominance

heterozygous genotype produces an intermediate phenotype; neither allele dominants the other

hypercholesterolemia

recessive disorder that causes cholesterol levels to be many times higher than normal, example of incomplete dominance

codominance

both alleles express themselves fully in a heterozygous organism

polygenic traits

traits affected by more than one gene

epistasis

two separate genes control one trait, but expression of one gene masks the expression of another gene (so that gene is epistatic to the gene it masks) ex: in guinea pigs; production of melanin masks deposition of melanin

wild type phenotype

more common phenotype for a trait in fruit flies

mutant phenotypes

traits are different from the normal

Duchenne's musclar dystrophy

X-linked trait, absence of an essential muscle protein

hemophilia

X-linked trait, absence of a protein vital to clotting proceses

red-green colorblindness

X-linked trait, unable to distinguish between colors

X inactivation

one of two X chromosomes remains as a Barr body (in every female), creates genetic mosiac: some cells have one X inactivated, other cells have other X inactivated, ex: female calico cats (traits for black/yellow fur); sweat glands in humans

Barr body

genes that are not expressed

holandric trait

traits inherited via the Y chromosome

linkage map

genetic map put together using crossover frequencies, the farther apart two genes are on a chromosome, the more likely they are to cross-over

map unit (centigram)

in chromosome mapping, an increment of 1 percent in the frequency of crossing-over

law of multiplication

to determine the probability that two random events will occur in succession, you simply multiply the probability of the first event by the probability of the second event

pedigrees

family trees used to describe the genetic relationships within a family, males square and females circles, figure out by process of elimination of disease being dominant/recessive autosomal/sex-linked

Tay-sachs disease

recessive genetic disorder; body is unable to break down a type of brain lipid

cystic fibrosis (CF)

recessive genetic disorder, excessive secretion of a thick mucus that accumulates in the lungs

sickle cell anemia

recessive disorder; formation of a hemoglobin protein that is less efficient at carrying oxygen

phenylketonuria (PKU)

autosomal recessive disease; unable to digest amino acid phenylalanine

Huntington's disease

dominant disorder; breakdown of nervous system

aneuploidy

production of offspring with an abnormal number of chromosomes

Down's syndrome

aneuploid; trisomy-21

Patau syndrome

trisomy 13; brain and circulatory defects

Edwards syndrome

trisomy 18; affects all organs

Klinefelter syndrome

XXY; male sex organs but female body characteristics

Turner's symdrome

XO; females possess sex organs that fail to mature at puberty

deletion

piece of chromosome is lost in the developmental process

cri-du-chat syndrome

deletion in chromosome 5

chromosomal translocations

a piece of one chromosome is attached to another, nonhomologous chromosome

chronic myelogenous leukemia

example of translocation; cancer affecting white blood cells

chromosome inversion

portion of chromosome separates and reattaches in the opposite direction

chromosome duplication

repetition of a genetic segment

Gregor Mendel

bred garden peas to study patterns of inheritance and applied statistical analysis to data, theory of particulate inheritance: inherited characteristics are carried by discrete units called elementes (genes), and not mixing

probability

multiply the probability of two independent events happening; then add them when more than one arrangement of the events is possible

dihybrid cross

cross between individuals that are hybrid for two different traits (TtYy x TtYy), yields offspring with phenotypic ratio of 9:3:3:1

multiple alleles

more than two allelic forms of a gene, ex: ABO blood groups

penetrance

frequency with which individuals of a given genotype manifest at least some degree of a specific mutant phenotype, ex: blue sclera in humans is dominant, but only 90% exhibit trait

expressivity

range of expression of mutant genes, ex: polydactyly- can have only crooked finger to extra entire toe

nurture versus nature

the development of intelligence is the result of an interaction of genetic predisposition and the environment

sex-influenced inheritance

influenced by the sex of the individual carrying the traits, ex: male-pattern baldness

sex-linked traits

carried on the X chromosome, ex: color blindness, hemophilia, Duchenne muscular dystrophy, sons must inherit it from mother, since inherits Y chromosome from father

mutations

any changes in the genome, occur in the somatic cells, gene mutation: change in DNA sequence, chromosome mutation: karyotypes, able to be seen under a microscope

examples of autosomal gene mutations

recessive: PKU, cystic fibrosis, tay-sachs disease, dominant: Huntingdon's disease, sex-linked: hemophilia, color blindness, duchenne musclar dystrophy

genomic imprinting

certain traits' expressions varies depending on which parent they are inherited from, ex: Prader-Willi syndrome- mental retardation, short stature, ex: Angelman syndrome: jerky, spontaneous laughter, same mutation, but Prader-Willi is from father and Angelman is from mother, also fragile X syndrome

fragile X syndrome

most common cause of mental retardation, example of genomic imprinting, tip of X chromosome hangs on by a threat as a series of repeated CGG nucleotides, 6-54 is normal; 55-200 is carrier; >200 expresses syndrome, dominant

extranuclear inheritance

found in mitochondria and chloroplasts, always inherited from mother, ex: in mitochondria, reduce ATP production-> affects nervous system and muscles that use up a lot of energy