Chapter 8: Patterns of Inheritance Flashcards
define character
- a heritable feature
- flower color
define trait
- specific characteristic of an individual
- purple flower or white flower
define gene
- basic unit of heredity passed from one generation to the next
- region of DNA encoding a product
define allele
- different versions of the same gene
- different sequence of nucleotides
- each individual has two for each gene
- P and p
define phenotype
- physical appearance of an organism
- purple flower or white flower
define genotype
- genetic makeup of an organism
- what alleles you have
- PP, Pp, pp
define locus
- specific locations on a chromosome where a gene is found
define monohybrid cross
- cross between two true-breeding parents that express different traits for one characteristics
- PP x pp
define dihybrid cross
- cross between two true-breeding parents that express different traits for two characteristics
- PPYY x ppyy
define test cross
- cross between dominant expressing organism whose genotype you don’t know and a homozygous recessive organism for the same characteristic
- determines the genotype of the dominant expressing parent
define reciprocal cross
- paired cross in which respective traits of the female and female in one cross become respective traits of the female and male in the next cross
- phenotype switches genders
define discrete
- characteristics that are in a either/or manner
- one or the other
- white OR purple
- yellow OR green
- wrinkled OR smooth
define true-breeding
- organisms that always pass a specific phenotype to the next generation
- homozygous
define P generation
- true-breeding parents
- both homozygous for different traits (PP x pp)
- manually crossed
define F1 generation
- offspring of P generation
- hybrids
- heterozygous (Pp)
define F2 generation
- offspring of F1 generation from self-pollination
- all genotypes expressed (PP, Pp, pp)
- creates 3 to 1 ratio of phenotypes
define dominant
- allele that is expressed over recessive allele
- PP or Pp
- purple flower color was dominant in mendel’s experiments
define recessive
- allele expressed only in absence of dominant allele
- pp
- white flower color was recessive in mendel’s experiments
define continuous variation
- range of difference among individuals for a characteristic
- offspring look like a blend of their parents
define discontinuous variation
- each individual shows one of two (or few) easily distinguishable and distinct traits
- what mendel observed
who is known as the father of genetics
gregor mendel
what did gregor mendel do
- set principles of genetics: principle of heredity and mechanism of inheritance
- did experiments through pea plant model system
- discovered 2 laws of inheritance
what are the 2 laws of inheritance that gregor mendel discovered
- law of segregation
- law of independent assortment
why did gregor mendel study peas
- available in many varieties
- easy to control mating of plants
- used them to feed a monastery
describe mendel’s pea experiments
- manually cross-pollinated pea plants
- worked with thousands of plants over 8 years
- looked at many characteristics: flower color, seed color, seed texture, plant height, etc
- worked with discrete characteristics
- mated contrasting true-breeding parents (hybridization)
what 4 concepts helped to explain the 3:1 phenotypic ratio mendel obseved
- concept of alleles
- each characteristic has multiple alleles and each individual has 2
- individuals can have differing alleles, heterozygotes
- law of segregation
define mendel’s law of segregation
- alleles/chromosomes segregate during meiosis
- gametes have equal change of receiving either allele/chromosome
- only one allele/chromosome is carried in a particular gene
how did mendel discover the law of segregation
following a single characteristic
define mendel’s law of independent assortment
- each pair of alleles/chromosomes segregates without influence of other alleles/chromosomes
- random combinations of alleles into gametes
- gamete with R allele has equal chance of also have Y or y
how did mendel discover the law of independent assortment
following two characteristics at the same time, dihybrid cross
what do results of a test cross tell you
- genotype of dominant expressing parent (PP or Pp)
- all offspring expressing dominant phenotype mean parent in homozygous dominant
- offspring express dominant and recessive phenotype in 1:1 ratio means parent is heterozygous
how many boxes will a punnett square have for 1, 2, 3, 4, and 5 genes
- 1: 4
- 2: 16
- 3: 64
- 4: 256
- 5: 1024
define probability
- fraction or decimal equivalent over a range of 0 to 1 or out of a percentage 0% to 100%
what does a probability of 0 and a probability of 1 mean
- 0: event will not happen, not due to chance
- 1: event will happen, not due to chance
define chance
- anything that ranges between 0 and 1
- ex: chance of flipped coin landing on head = 0.5
what is the multiplication rule of probability
- 2 or more independent events will occur together
- product of individual probabilities
- AND
- chance of rolling a 5 on the first die AND a 4 on the second = 1/6 x 1/6 = 1/36
what is the addition rule of probability
- probability that one event or the other will occur
- adding individual probabilities
- OR
- chance of rolling a 4 OR a 5 = 1/6 + 1/6 = 1/3
what are the rules of probability used for
- predicting outcome of crosses
- can be used together for complex events
how do you calculate the chances of various genotypes
- each character/gene is calculated separately
- individual probabilities then multiplied together
what is the probability that an individual offspring has the genotype AaBBCCDd with both parents being AaBbCcDd
- calculate probability of each allele combination using punnett square: Aa= 1/2, BB= 1/4, CC= 1/4, Dd= 1/2
- multiply individual probabilities together: 1/2 x 1/4 x 1/4 x 1/2 = 1/64
define complete dominance
- phenotypes of heterozygote and dominant homozygote are identical
- dominant trait masks recessive
- purple flowers
define incomplete dominance
- phenotype of F1 hybrids are between the phenotypes of two parents
- 3 phenotypes are usually seen
- blended mix
define codominance
- 2 dominant alleles affect phenotype in separate but distinguishable ways
- human blood type
- unblended mix
define multiple alleles
- genes with more than 2 alleles (very common)
- each organisms can only have 2
- wide variety in phenotypes
- some alleles are dominant to others and recessive to others
- blood type in humans determined by 3 alleles (A, B, O)
define pleiotropy
- many influencing
- a gene has multiple phenotypic effects
- an allele causes multiple characteristics
define polygenic
- many genes
- opposite of pleiotropy
- characteristic determined by 2 or more genes
define quantitative inheritance
- human characteristics that vary in the population
- indicates polygenic inheritance: additive effect of 2 genes on single phenotype
define epistasis
- a gene at 1 locus alters the phenotypic expression of a gene at another locus
define multifactorial
- influences by both genetics and environmental factors
- includes heart disease and cancer
examples of human characteristics that follow mendelian inheritance patterns
- earlobe attachment
- tongue rolling
- photic sneezing
- marfan syndrome
- huntington’s syndrome
what things did mendel’s experiments suggest
- two types of alleles exist for every gene
- alleles maintain their integrity for each generation (no blending)
- dominant allele always masks the recessive allele
do the fundamental principles of mendelian genetics still hold true
- yes
- but we know more complexity exists
are dominant alleles aways more common in a population
- no
- polydactyly is dominant but still rare
define lethality
- some alleles are so non-functional that they lead to death of the individual
- can be dominant or recessive
example of lethality in manx cats
- MM are normal housecats
- MML are manx
- MLML results in early embryotic death
example of pleiotropy in humans
- red hair color gene
- codes for red hair, increased pain tolerance, requiring more anesthesia, lower UV protection
example of polygenic trait/epistasis in dogs
- coat color in labs
- B locus: determines color of pigment produced
- E locus: determines if pigment is deposited in hair follicles
