Chapter 14 Flashcards
What is character, and an example?
heritable feature that varies among individuals
example- flower color
What is a trait?
variant for a character
What is Mendel’s Pea Experiment? (6)
Ensured cross-pollination by removing the stamen of a pea plant and brushing pollen from another plant
Prevented self-pollination
Results in a zygote that develops into a plant embryo in a seed
Only tracked characters in two distinct, alternative forms (flower color)
Only did true breeding
Cross pollinated two contrasting varieties
What is true breeding? (2)
When parents always produce the same variety in the offspring
example- purple pea flowers always producing purple flowers
What is hybridization? (4)
Breeding two contrasting varieties
P generation- true-breeding parents
F1 generation- first filial generation
breeding of F1 generation plants produces F2 generation plants
What is the law of segregation? (5)
During Mendel’s experiment, the F1 generation was purple
F2 generation had a ratio of purple to white 3:1
Purple flowers were dominant
White flowers were recessive
This means white flower traits were hidden in the presence of the purple flower trait
What are Mendel’s Model concepts? (4)
Alternative versions of genes account for variations in inherited characters
For each character, an organism inherits two alleles of a gene, one from each parent
If two alleles at a locus differ, one is dominant (determines appearance) one is recessive
Law of segregation- two alleles for a heritable character segregate during gamete formation and end up in different gametes
What are alleles?
Alternative versions of genes
What is a Punnett square?
diagrammatic device predicting allele composition of offspring from a cross between individuals of known genetic makeup
What is a homozygous organism? (2)
organism with a pair of identical alleles for a character
Results from true breeding
What is a heterozygous organism?
organisms with two different alleles for a gene
What is a phenotype?
organism’s appearance or observable trait
What is a genotype?
organism’s genetic makeup
What is a testcross? (4)
Determines whether an organism is homozygous or heterozygous
Crosses said organism with a recessive homozygous allele
If all offsprings result with dominant traits, the mystery organism is homozygous
If offsprings result with various traits, the mystery organism is heterozygous
What are monohybrids? (2)
organisms that are heterozygous for one particular character being followed
F1 generation in Mendel’s experiment
What is a monohybrid cross? (2)
cross between monohybrid heterozygotes
Results in a 3:1 ratio between dominant: recessive
What is a dihybrid? (3)
individuals that are heterozygous for the two characters being followed in the cross
YyRr
Results in a 9:3:3:1 YR:Yr:yR:yr
What is the law of independent assortment? (4)
two or more genes assort independently
Each pair of alleles segregates independently of
each other pair of alleles during gamete formation
Applies only to genes located on different chromosomes
Nonhomologous
How do alleles segregate, and an example?
Independently of another gene’s alleles
example- a coin toss always has a ½ probability of being tails no matter the previous coin toss’ result
What is the multiplication rule for a monohybrid cross? (5)
Used to determine the probability of two or more independent events will occur together in some specific combination
Example- chance of two coins tossed at the same time with both resulting in tails
We multiply the probability of one event by the probability of the other event
Example: ½ (chance of one coin being tails) * ½ (probability of other coin being tails)= ¼
Example: when gametes fuse to form a zygote: ½ (probability of a sperm to have recessive trati) * ½ (probability of an egg to have a recessive trait)= ¼
What is the addition rule for a monohybrid cross? (4)
The probability that any one of two or more mutually exclusive events will occur
Used to determine the probability that an F2 organism from a monohybrid cross will be heterozygous
For example: dominant allele can come from the egg and the recessive allele can come from the sperm or vice versa
Gametes can combine to form heterozygous offspring in two mutually exclusive ways
How do you calculate a genetic problem?
example-
In monohybrid cross, Yy has
¼ chance being YY, ½ chance of being Yy, and ¼ chance being yy
In monohybrid cross Rr
¼ chance being RR, ½ chance being Rr, and ¼ chance being rr
To determine the dihybrid probability of YYRR
¼ (YY) * ¼ (RR)= 1/16
To determine the dihybrid probability of YyRR
½ (Yy) * ¼ (RR)= ⅛
How to calculate three or more character crosses
Ex: PpYyRr * Ppyyrr
First, list all genotypes that fulfill asked condition
ppyyRR, PpYyRr, ppYyRr, etc.
Calculate the probability by multiplying individual allele pairs
ppyyRr= ¼ * ½ * ½
When a heterozygous and homozygous allele pairs cross, the probability of heterozygous offspring is ½
Add together the chances of the asked condition
How can an inheritance of a gene deviate from Mendelian patterns? (3)
Inheritance of characters determined by a single gene can deviate from Mendelian patterns when alleles are not completely dominant or recessive
When genes have more than two alleles
When a single gene produces multiple phenotypes
What is complete dominance? (3)
phenotype of the heterozygote and the dominant homozygote are indistinguishable
When the dominant allele overpowers the recessive allele
Example- Mendel’s peas, with purple flowers showing complete dominance
What is incomplete dominance? (2)
-when hybrids have a phenotype somewhere between those of two parental varieties
Example- when a red and white snapdragon crosses to produce pink snapdragons
Results when heterozygote offspring has less red pigment than the homozygous parent
What is codominance?
wo alleles each affect the phenotype in separate, distinguishable ways
What is an example of codominance? (4)
MN blood groups
Homozygous M allele have red blood cells with only M molecules
Homozygous N alleles have red blood cells with only N molecules
Heterozygous MN groups have both M and N alleles and result with distinguishable effects from both groups
How do dominance and phenotype interact? (2)
When dominant alleles and recessive alleles coexist in a heterozygote, they do not interact
During the path from genotype to phenotype, dominance, and recessiveness comes into play
What is an example of dominance and phenotype? (5)
Mendel’s round (dominant) vs wrinkled (recessive) pea seed shape
The dominant allele has the code for an enzyme that converts unbranched forms of starch to branched from in the seed
Recessive allele codes for a defective form of the said enzyme, leading to an accumulation of unbranched starch
Excessive water enters the seed through osmosis. As the seed dries, it wrinkles
Dominant allele present prevents excess water from entering the seed and prevents wrinkling when drying
How do allele and phenotype correlate?
For any character, the observed dominant/ recessive relationship of alleles depends on the level at which we examine the phenotype
How does Tay-Sachs disease differ in dominant/recessive relationship? (7)
Tay Sachs disease (cannot metabolize certain lipids because of defective enzymes, causing excess lipids)
Results when a child inherits two copies of the Tay Sachs allele (homozygotes)
Organismal level- recessive
Biochemical level- incomplete dominance
Heterozygote lipid metabolization is between homozygous of normal alleles and homozygous of tay-sachs disease
Heterozygotes have enough lipid metabolization to prevent disease
Molecular level- codominant
Heterozygous individuals produce equal numbers of normal and defective enzymes
What is the frequency of dominant alleles? (3)
Dominant alleles are not always more common
Example polydactyly (extra finger/ toe)
For those with polydactyly, the presence of a dominant allele results with said disorder
How do multiple alleles interact? (6)
Although Mendel’s pea character’s genes had only two alleles, most genes have more
Example- ABO blood groups
Determined by three alleles: IA (type A), IB (type B), i (none)
Results with one of four types, A, B, AB, or O
A and B are carbohydrates found on the surface of red blood cells
O have neither
What is pleiotropy?
Genes having multiple phenotypic effects
Associated with multiple symptoms of certain hereditary diseases like cystic fibrosis and sickle-cell disease
In garden peas, gene determining flower color also affects the color of the seed coat
What is epistasis?
Phenotypic expression of a gene at one locus alters that of a gene at a second locus
What is an example of epistasis? (5)
labrador retrievers
Black coat is dominant to brown coat (Bb)
Genotype must be bb for a brown coat
Second gene determines whether pigment will be deposited in the hair (Ee)
If second gene is homozygous recessive (ee), coat is yellow, no matter the genotype of black/ brown locus
What is polygenic inheritance? (2)
Mendel studied characters as either or
Either purple or white flowers
Many characters are not discrete
Skin color or height
What are quantitative characters? (3)
characters that vary in the population in gradations along a continuum
Indicates polygenic inheritance
Additive effect of two or more genes on a single phenotypic character
What is an example of quantitive colors? (4)
Skin pigmentation- consists of three units of alleles- A, B, or C
AABBCC is very dark
aabbcc is very light
AaBbCc is median
Same shade as aaBBCc
How do nature and nurture affect phenotype? (5)
The environment can affect phenotype
Example- tree having various leaf size, shape, greenness, depending on exposure to wind and sun
Example- humans having various height (nutrition), build (exercise), and skin shade (sun tanning)
Genotype is not associated with a rigidly defined phenotype
Blood count is affected by factors like altitude, physical activity, and infectious agents
What does multifactorial mean?
many factors influencing phenotype
What is pedigree? (2)
a family’s history for a particular trait
Collecting information on said trait by looking through the family tree
What are carriers? (2)
carry recessive alleles responsible for a disorder
Heterozygotes that do not exhibit the disorder but carry the recessive allele
How does inbreeding affect inheritance?
Inbreeding raises chances of passing recessive alleles because they share common ancestors that are more likely to carry the same recessive allele
What is cystic fibrosis? (5)
Most common lethal genetic disease in the US
More common in European descendants
Defective chloride transport chains in the plasma membrane
Results in a high concentration of chloride in the extracellular matrix
Causes mucus buildup in the organs
How do recessive genes and sickle cell disease interact? (4)
Two recessive sickle cell alleles are necessary for full-blown disease
The presence of one allele can affect phenotype
Organismal level- incomplete dominant
Molecular level- codominant
What are examples of dominantly inherited disorders? (4)
Achondroplasia- dwarfism
99.9% of the population are homozygous for the recessive allele
Huntington’s disease- a degenerative disease of the nervous system
A dominant lethal allele that shows no phenotypic effect until 35-45 years
What are multifactorial disorders? (2)
Genetic component plus the significant environmental influence
Example-heart disease, diabetes, cancer, alcoholism, schizophrenia, bipolar disorder
What is amniocentesis? (3)
technique to determine whether a fetus has tay sachs disease
Done in the 14th -16th week
Doctor inserts a needle in the uterus and extracts amniotic fluid
What is chorionic villus sampling?
doctor inserts a narrow tube through the cervix into the uterus and suctions a sample of tissue from the placenta
What are imaging techniques? (3)
examines fetus for major anatomical abnormalities
Ultrasound- sound waves used to produce an image
Fetoscopy- needle-thin tube containing a viewing scope is inserted in the uterus
What is an example of newborn screening?
phenylketonuria- a recessively inherited disorder
Cannot metabolize amino acid phenylalanine
This acid and phenylpyruvate accumulate in the blood and causes mental retardation
If detected early, a special diet low in phenylalanine will allow normal development
