until the 1900s, what did most scientists believe about inheritance?
many scientists believed that traits in offspring were a blend of parental traits (aka blending hypothesis or theory)
(1) (1800s) discovered the fundamental mechanism by which traits are inherited, (2) work was not recognized until 1900s, (3) one of the first scientists to use mathematical analysis in a quantitative experiment
what did Darwin's theory of natural selection lack?
a mechanism to explain how traits are inherited
the way traits are passed on from generation to generation
theory of blending inheritance
(1) formed in the 1800s, (2) advocated that traits present in the parents mixed together like paint to produce a new combination in the offspring, (3) based on the observation that offspring can have some characteristics of the mother or father, but typically are not identical to either one
(1) in 1700s, conducted formal plant breeding experiment, (2) concluded that males and females both contribute to the appearance of traits
(1) consists of two crosses in which possession of two alternate forms of a trait by each sex is reversed, (2) produce identical offspring, (3) example:
((yellow male) X (green female)
(green male) X (yellow female))
how was Mendel able to manipulate pea plants to determine the mechanism of inheritance?
pea flower pollen is contained in the anther and can be removed from the plant and used to fertilize another flower's ovules contained in the carpel (hand pollination)
artificial selection of plants
Gregor Mendel's study of what subject was crucial in his ability to analyze his hybridization experiments?
the process of crossing two genetically different parent plants to produce offspring with traits of both parents
put the events in Mendel's life in chronological order
(1) Mendel enters monastery, (2) Mendel fails exam to become teacher, (3) Mendel studies statistics at the University of Vienna, (4) Mendel put in charge of the monastery gardens, (5) Mendel performs experiments on pea plants in order to study inheritance, (6) Mendel gives talk describing his research, (7) Mendel's paper is published
(aka P) refers to the initial cross between two organisms
first filial generation
(aka F1) offspring produced directly from a genetic cross
second filial generation
(aka F2) offspring resulting from interbreeding of the F1 generation
what happened when Mendel crossed alternate forms of a single trait?
one of the forms disappeared in the F1 generation, and then reappeared in the F2 generation
how many true-breeding pea plant traits did Mendel examine?
seven, each having two alternate forms of a single trait
form of the trait that masks other traits (the trait that is expressed whenever present)
form of the trait that is masked by the dominant trait (the trait that is expressed only if the dominant trait is not present)
in what ratio did the dominant and recessive traits appear in Mendel's F2?
what are three reasons that Mendel succeeded in determining the principles of inheritance?
(1) he started experiments with pure-breeding lines of plants, (2) he chose an organism that existed in many different easily distinguishable varieties, (3) he happened to have chosen traits that were located on different chromosomes
breeding experiment that uses parent varieties that differ in a single trait
genetic studies in the 1900s often used the fruit fly as a model. Why did early studies of inheritance in the 1700s and 1800s use plants?
(1) plants are inexpensive to grow, (2) plants are easy to manipulate, (3) true breeding plant strains were readily available
To investigate patterns of inheritance, Mendel looked at traits that
were dichotomous in nature
divided or dividing into two sharply distinguished parts or classifications
alternate form of a gene
discrete units of heredity
from his work with pea plants, what did Mendel hypothesize?
(1) the factors (genes) consist of pairs of alternate forms (alleles), (2) each trait was controlled by a pair of alleles
law of segregation
says that the pairs (alleles) segregate and each parent donates only one to the offspring
condition that occurs when an organism has two identical alleles for a gene (noun: homozygote)
condition that occurs when an organism has two different alleles for a gene (noun: heterozygote)
because of the law of segregation, when two heterozygotes are crossed how many types of genotypes and phenotypes result?
three different genotypes, and two different phenotypes
allelic composition of a trait, or traits, of an individual
outward manifestation of a particular genotype
what are the steps to determine the probabilities of genotypic and phenotypic frequency?
(1) identify dominant and recessive alleles, (2) determine parental genotypes, (3) set up a Punnett square that shows the gametic contributions of the mother and father, (4) examine the probable genotypic and phenotypic frequencies in offspring
A test-cross is done to determine an unknown genotype. In this cross, the unknown genotype is crossed with a
homozygous, recessive genotype
breeding experiment that uses parent varieties that differ in a single trait
law of independent assortment
states that alleles for two different traits segregate independently of each other
in the F2 generation, what was Mendel's outcome ratio when he experimented with a dihybrid cross?
Mendel's laws of segregation and independent assortment follow what two rules of probability?
the multiplicative rule, and the additive rule
the probability of two independent events co-occurring is the product of their individual probabilities
the probability of one OR another of two mutually exclusive (or separate) events occurring equals the sum of their individual properties
(noun: test cross) a cross between an organism whose genotype for a certain trait is unknown and an organism that is homozygous recessive for that trait
(1) the heterozygote genotype has a unique phenotype which is intermediate to the two parental phenotypes; neither allele dominates, (2) example: snapdragons (red x white = pink)
(1) both alleles of a heterozygote are distinctly expressed, (2) example: cattle (red-brown x white = roan (some red-brown and some white hairs)
is incomplete dominance evidence for the blending hypothesis?
although the occurrence seems to provide evidence for the blending theory of inheritance, crossing the F1 plants yields F2 plants that are red, pink, and white in a 1:2:1 ratio. If the characteristics had blended together the F2 plants would all be be pink. The 1:2:1 ratio shows that Mendel's law of segregation is upheld
what are the four blood types in humans?
type A, type B, type AB, and type O
which type displays codominance?
when a gene has more than two possible alleles
what governs blood transfusions between the various blood groups?
the presence or absence of antibodies in the blood
how are blood groups classified?
by the type of glycolipid (or antigens) embedded in the cell membrane of the red blood cell
what type of antigens on the surface of the cell does type A blood have?
what type of antigens on the surface of the cell does type B blood have?
what type of antigens on the surface of the cell does type AB blood have?
both A and B antigens
what type of antigens on the surface of the cell does type O blood have?
none, neither A nor B antigens
why are the glycolipids in blood cells called antigens?
the glycolipids are called antigens because they have an antigenic effect with certain other blood types
any substance that stimulates an immune response in the body
what type of antibodies does type A blood have?
B antibodies (attacks B antigens -- type B, AB blood)
what type of antibodies does type B blood have?
A antibodies (attacks A antigens -- type A, AB blood)
what type of antibodies does type AB blood have?
none, neither A nor B antibodies
what type of antibodies does type O blood have?
(1) both A and B antibodies (attacks A and B antigens -- type A, B, and AB blood), (2) therefore, an individual with type O blood can only accept type O, (3) however, type O can be given to individual with any type of blood, because it doesn't cause enough damage to cause a problem
which blood type is known as the universal acceptor?
which blood type is known as the universal donor?
what is/are the genotype(s) for type A blood?
(1) I^A I^A, (2) I^A i
what is/are the genotype(s) for type B blood?
(1) I^B I^B, (2) I^B i
what is/are the genotype(s) for type AB blood?
what is/are the genotype(s) for type O blood?
what blood type(s) can type A blood accept?
type A blood, type O blood
what blood type(s) can type B blood accept?
type B blood, type O blood
what blood type(s) can type AB blood accept?
type A blood, type B blood, type AB blood, type O blood
what blood type(s) can type O blood accept?
type O blood
how many alleles are responsible for producing the four possible blood type phenotypes in humans?
I^A, I^B, and i
present information categorized into a family tree to trace the inheritance of various traits (including disorders) through generations
in pedigree charts, what do squares represent?
in pedigree charts, what do circles represent?
in pedigree charts, what do horizontal lines represent?
in pedigree charts, what do vertical lines represent?
connects children to parents
what two genetic factors control blood type?
codominance and multiple alleles
(1) interaction of two or more genes in producing a given phenotype; one gene's product affects/modifies another gene, (2) usually has a phenotypic ratio of 9:3:4 or 12:3:1 (a modification in the 9:3:3:1 phenotypic ratio expected from a dihybrid cross)
(plural: loci) specific site of a particular gene on its chromosome
named for a seemingly impossible blood type in an Indian child. The occurrence of the phenotype, which involves epistasis, led to the discovery of a previously unknown second gene that influences ABO blood type
in the presence of the dominant H allele, a protein precursor is...
converted to A or B antigens
when the genotype is hh, the precursor is...
not converted, resulting in type O blood, regardless of the presence of A or B antigens
(1) characters that vary in a continuous manner, (2) vary in populations along a continuum because many variations of phenotype exist, (3) example: height
(1) the phenomenon of the influence of two or more genes that may have an additive effect on a single phenotypic character, (2) because of polygenic inheritance, the parental phenotypes may vary greatly from offspring phenotypes
(1) when one gene affects many (more than one) phenotypic traits, (2) commonly occurs in human genetic disorders, (3) examples of disorders with pleiotropic effects: sickle cell anemia, cystic fibrosis, Tay-Sachs
why are some genetic disorders more common within one race or ethnic group?
until recently, ethnic and racial groups have been genetically isolated
lethal recessive genetic disorder
a disorder that is expressed in the homozygous state. These disorders are lethal unless the person receives medical care for the symptoms of the disease. Most sufferers of lethal recessive disorders die as a result of the disorder.
(1) caused by a defect in the transport protein of the cell membrane, (2) affects 1/2500 people of European descent, (3) pleiotropic effect is mucus build-up in the pancreas, lungs, and digestive tract
sickle cell anemia
(1) caused by a point mutation (specifically a missense mutation), which creates a defect in the hemoglobin protein of red blood cells, and is transmitted by infected mosquitoes (2) occurs in 1/400 African Americans, (3) pleiotropic effects are physical weakness, anemia, heart failure, and brain damage, (4) occurs when the amino acid valine replaces the normally occurring amino acid glutamic acid
(1) manifests itself during infancy, caused by a defect in an enzyme that breaks down lipids in the brain, (2) prevalent among people of European Jewish descent, (3) pleiotropic effects are mental retardation, failure to develop control of muscles, blindness, and ultimately, death in early chidhood
recessively inherited disorder
occurs when individuals with two defective alleles express the disease (hh). The alleles result in a nonfunctioning enzyme. Heterozygotes (Hh) have one normal enzyme and do not display the disease
dominantly inherited disorder
(1) occurs when one defective allele results in a phenotypic effect (D_). Heterozygotes (Dd) have one defective allele and display the disease, (2) example: Huntington's disease
why can the sickle cell allele and the normal allele be considered codominant on the cellular level?
A person that is heterozygous and has one allele causing sickle cell and one normal allele will produce both sickled and normal red blood cells
(1) describes a condition in which a heterozygote for a trait displays some selective advantage over homozygotes, (2) example: in sickle cell anemia, the heterozygous condition gives protection from malaria. Individuals who carry one gene for sickle cell anemia are more likely to survive in situations where malaria is present
(1) genes located on the same chromosome, (2) do not assort independently, (3) can produce only two kinds of gametes (two unlinked genes can produce four kinds of gametes), (4) offspring do not display 9:3:3:1 phenotypic ratio (usually linked genes have a 1:2:1 phenotypic ratio), (5) decreases genetic variation
all of the alleles that occur on a given chromosome
Thomas Morgan Hunt
a geneticist who (1) proved that a specific gene is carried on a specific chromosome, (2) found that genes can be linked to each other on a chromosome, (3) discovered sex-linked traits (meaning that genes are on sex chromosomes)
exchange of genetic material that occurs during synapsis in meiosis I
offspring with an appearance that differs from either of the parents