chapter 14
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183 Terms
What is a character?
A heritable feature that varies among individuals.
What is a trait?
A specific variant of a character.
What is an example of a character?
Flower color.
What is an example of a trait for flower color?
Purple flowers or white flowers.
What is a gene?
A unit of heredity that influences a character.
What is an allele?
An alternative version of a gene.
What is true-breeding?
Producing offspring of the same variety after many generations of self-pollination.
What is the P generation?
The parental generation in a genetic cross.
What is the F1 generation?
The first filial generation, or offspring of the P generation.
What is the F2 generation?
The offspring produced when F1 individuals mate or self-pollinate.
Why were pea plants useful for Mendel's experiments?
They had many varieties, short generation times, many offspring, and controlled mating.
What is self-pollination?
Transfer of pollen to the same flower or plant.
What is cross-pollination?
Transfer of pollen between different plants.
What is the blending hypothesis?
The incorrect idea that parental traits permanently mix in offspring.
How did Mendel's experiments disprove blending inheritance?
A recessive trait reappeared unchanged in the F2 generation.
What is a dominant allele?
An allele expressed in the phenotype of a heterozygote.
What is a recessive allele?
An allele masked in a heterozygote.
What is complete dominance?
The heterozygote has the same phenotype as the homozygous dominant individual.
What is genotype?
An organism's allele combination.
What is phenotype?
An organism's observable traits.
What is a homozygote?
An organism with two identical alleles for a gene.
What does homozygous mean?
Having two identical alleles.
What is a heterozygote?
An organism with two different alleles for a gene.
What does heterozygous mean?
Having two different alleles.
Why are heterozygotes not true-breeding?
They can produce offspring with different phenotypes.
What is a monohybrid?
A heterozygote for one character.
What is a monohybrid cross?
A cross between two individuals heterozygous for one character.
What is a dihybrid?
An organism heterozygous for two characters.
What is a dihybrid cross?
A cross between individuals heterozygous for two characters.
What is a testcross?
A cross between an individual with a dominant phenotype and a homozygous recessive individual.
Why is a testcross used?
To determine an unknown dominant genotype.
What is Mendel's first law?
The law of segregation.
What does the law of segregation state?
The two alleles for a gene separate during gamete formation.
When do alleles separate during meiosis?
When homologous chromosomes separate in meiosis I.
How many alleles for a gene does a gamete receive?
One allele.
What is Mendel's second law?
The law of independent assortment.
What does the law of independent assortment state?
Allele pairs segregate independently during gamete formation.
When does independent assortment occur?
During the random orientation of homologous pairs in metaphase I.
When does independent assortment apply most reliably?
When genes are on different chromosomes or far apart on the same chromosome.
Why can nearby genes fail to assort independently?
They are linked on the same chromosome.
What is the expected phenotypic ratio from Pp × Pp?
3 dominant phenotype to 1 recessive phenotype.
What is the expected genotypic ratio from Pp × Pp?
1 PP to 2 Pp to 1 pp.
What is the expected phenotypic ratio from YyRr × YyRr?
9:3:3:1.
What gametes can a YyRr individual produce?
YR, Yr, yR, and yr.
What is probability?
The likelihood that an event will occur.
What is the probability of a certain event?
1.
What is the probability of an impossible event?
0.
What is an independent event?
An event whose outcome does not affect another event's outcome.
What is the multiplication rule?
Multiply probabilities of independent events that must both occur.
What is the addition rule?
Add probabilities of mutually exclusive outcomes.
When should the multiplication rule be used in genetics?
When outcomes must occur together.
When should the addition rule be used in genetics?
When different possible outcomes can produce the same result.
What is incomplete dominance?
A heterozygote has an intermediate phenotype.
What is the snapdragon example of incomplete dominance?
Red × white flowers produce pink heterozygotes.
What genotype represents a red snapdragon?
CRCR.
What genotype represents a white snapdragon?
CWCW.
What genotype represents a pink snapdragon?
CRCW.
What is codominance?
Both alleles are fully and separately expressed in a heterozygote.
What is an example of codominance?
The AB blood type.
What are multiple alleles?
More than two alleles for a gene in a population.
How many common ABO blood-group alleles are there?
Three.
What are the ABO blood-group alleles?
IA, IB, and i.
What does the IA allele do?
It adds A carbohydrates to red blood cells.
What does the IB allele do?
It adds B carbohydrates to red blood cells.
What does the i allele do?
It adds neither A nor B carbohydrates.
What blood type results from IAIA or IAi?
Type A.
What blood type results from IBIB or IBi?
Type B.
What blood type results from IAIB?
Type AB.
What blood type results from ii?
Type O.
What is the relationship between IA and IB?
They are codominant.
What is the relationship between IA and i?
IA is dominant to i.
What is the relationship between IB and i?
IB is dominant to i.
What is pleiotropy?
One gene affects multiple phenotypic traits.
What is an example of pleiotropy?
Cystic fibrosis or sickle-cell disease.
What is epistasis?
A gene at one locus alters the phenotypic expression of a gene at another locus.
What gene determines black versus brown pigment in Labrador retrievers?
The B gene.
What gene determines whether Labrador pigment is deposited in hair?
The E gene.
What genotype produces a yellow Labrador retriever?
Any genotype with ee.
What is polygenic inheritance?
Two or more genes have additive effects on one phenotype.
What is quantitative variation?
Continuous variation in a trait across a population.
What usually causes quantitative variation?
Polygenic inheritance.
What is an example of polygenic inheritance?
Human skin color.
What is a multifactorial trait?
A trait influenced by multiple genes and environmental factors.
What does phenotype reflect?
Genotype and environmental history.
How can the environment influence phenotype?
It can alter how a genotype is expressed.
What is an example of environmental influence on phenotype?
Hydrangea color changes with soil acidity.
What is a pedigree?
A family tree showing inheritance across generations.
What can pedigrees help determine?
The likely inheritance pattern of a trait.
What does a shaded pedigree symbol indicate?
An affected individual.
What does a half-shaded pedigree symbol usually indicate?
A carrier.
What is a carrier?
A heterozygote with a recessive allele who is phenotypically normal.
How are recessive disorders expressed?
Only in homozygous recessive individuals.
What is albinism?
A recessive condition involving little or no skin and hair pigmentation.
What is cystic fibrosis?
A recessive disorder involving defective chloride transport channels.
What is a major effect of cystic fibrosis?
Thick mucus buildup and impaired nutrient absorption.
What is sickle-cell disease?
A recessive disorder caused by an altered hemoglobin protein.
What causes sickle-cell disease at the molecular level?
A single amino acid substitution in hemoglobin.
What is consanguineous mating?
Mating between close relatives.
Why does consanguineous mating raise recessive-disease risk?
Relatives are more likely to carry the same rare recessive allele.
What is achondroplasia?
A form of dwarfism caused by a dominant allele.