Mendelian Gentics And Beyond Flashcards
Phenotype
Expression of genotype; physical appearance (tall or short)
Inheritance
How traits are passed from parents to offspring
Blending model
Idea that genetic material from two parents blends together; leads to loss of variation; incorrect model
Particulate model
Idea that parents pass on discrete heritable units called genes; correct model
True breeding
Plants that produce offspring of the same variety when they self-pollinate
F1 generation
All plants were purple (heterozygous); showed that the blending model was not correct
F2 generation
3 purple : 1 white; factor for white flowers (recessive gene) was not diluted or destroyed because it reappeared in the F2 generation; consistent w/ particulate model
Genes
Discrete heritable units on chromosomes
What were the six characters of plants that Mendel observed?
Flower color (purple or white), seed color (yellow or green), seed shape (round or wrinkled), pod color (green or yellow), pod shape (inflated or constricted), flower position (axial or terminal), and stem length (tall or dwarf)
The particulate model currently recognizes that ___ are the hereditable units
Genes
Alleles
Alternative versions of genes (dominant or recessive)
Which allele is expressed over the other?
Dominant
Homozygous dominant and heterozygous will express the dominant trait
Genotype
Organism’s genetic makeup (RR or rr)
Diploid
Organisms w/ two copies of each chromosome
Homozygote
Organism w/ two identical alleles
Heterozygous
Organism w/ two different alleles
Mendel’s law of segregation
The two alleles for each character segregate (separate) during gamete production such that 50% of gametes receive one allele and 50% receive the other allele
Gamete
A haploid reproductive cell, such as an egg or sperm, that is formed by meiosis
Mendel used true breeding plants as the parents in his experiments. Which of the following characteristics describe true breeding plants:
They have dominant traits
They have recessive traits
They are heterozygous
They are homozygous
Both A and D
They are homozygous
What are the two laws of probability Mendel used?
Multiplication Rule and Addition Rule
Multiplication Rule
The probability that both of two independent events will occur is the product of the probability of their separate occurrences; look for “AND”
What is the probability of rolling a 1 AND then a 4 on two subsequent die rolls?
1/6 x 1/6 = 1/36
Addition Rule
The probability of an event that can occur in two or more mutually exclusive ways is the sum of the probability of their separate occurrences; look for “OR”
What is the probability of drawing a king OR queen from a deck of cards?
1/13 + 1/13 = 2/13 (15%)
Punnet squares
Measure the probability if genotypic outcomes (monohybrid crosses or dihybrid crosses)
If you cross a purple pea that is heterozygous (Pp) w/ a white pea (pp), what ratio of phenotypes will you see in the offspring?
50% purple, 50% white
What is the phenotypic ratio for two heterozygous parents of a dihybrid cross (YyRr x YyRr)
9:3:3:1
Mendel’s law of independent assortment
Each pair of alleles segregates independently of any other pair of alleles during gamete formation; only applies to genes on different, non homologous chromosomes or those far apart on the same chromosome
Difference between genes located on different non homologous chromosomes and genes on the same chromosome?
Genes located on the same chromosome tend to inherited together
A pea plant is heterozygous at the independent loci for flower color (Pp) and seed color (Yy). What types of gametes can it produce?
4 gamete types: pY, py, PY, and Py
Multi character cross
Equivalent to two or more independent monohybrid crosses occurring simultaneously
How do you solve a multi character cross?
Find the probabilities of each trait using individual punnet squares and then use multiplication rule
For the cross aaBbCC x AaBbcc, what is the probability of an offspring w/ the genotype aaBBCc?
1/8
When could inheritance of characters by a single gene deviate from simple Mendelian patterns?
When alleles are not completely dominant or recessive, when a gene has more than two alleles, and when a gene produces multiple phenotypes
Complete dominance
Occurs when phenotypes of the heterozygous and dominant homozygous are identical; normal
The situation in which the phenotypes of the heterozygous and dominate homozygous are indistinguishable
Incomplete dominance
The phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties; cross between a red flower and a white flower produces a pink flower; F2 generation produces a 1:2:1 phenotypic ratio (2 pink)
The situation in which the phenotype of heterozygotes is intermediate between the phenotypes of individuals homozygous for either allele
Codominance
Two alleles affect the phenotype in separate, distinguishable ways
Ex: cow hides are red or white
Red: RrRr
White: RwRw
A cow with RrRw has both red and white spots
Ex: human MN blood had different surfaces
LnLm has both M and N molecules on the surface of the red blood cells
The situation in which the phenotypes of both alleles are exhibited in the heterozygous because both alleles affect the phenotype in separate, distinguishable ways
Recessively inherited disorders
Show up only in individuals homozygous for the recessive allele (aa); most individuals w/ recessive disorders are born to carrier parents
Carriers
Heterozygous individuals who carry the recessive allele but are phenotypically normal
Tay-Sachs disease
Caused by a gene that had two alleles; one normal allele produces a functional enzyme, while the other mutant allele does not
At the organism level, mutant allele is recessive
At the biochemical level (enzyme activity), the alleles are incompletely dominant
At the molecular level (enzyme type), the alleles are codominant
Polydactly
Condition of having extra fingers and toes is caused by a dominant allele; having a dominant allele is less common than the recessive allele in populations of humans and other animals
What are the genotypes for the different ABO blood groups?
A: IAIA or IAi
B: IBIB or IBi
AB: IAIB
O: ii
What is the dominance relationship between the alleles for ABO blood type?
IA and IB are incompletely dominant
IA and IB are codominant
IA and IB are dominate to I
B and C are correct
B and C are correct
Pleiotropy
Most genes have multiple phenotypic effects; responsible for cystic fibrosis and sickle cell disease
Sickle cell disease
Recessive condition; disease allele codes for abnormal hemoglobin that causes sickle cell shaped red blood cells; symptoms include physical weakness, pain, organ damage, and even paralysis; heterozygous are less susceptible to the malaria parasite
Epistasis
One gene affects the phenotype of another due to interaction of their gene products
Polygenic inheritance
Multiple genes independent affect a single trait
Phenotypic plasticity
Ability of an organism to change in response to stimuli or inputs from the environment; Ex: hydrangeas grown in basic soul are pink while hydrangeas grown in acidic soil are blue
Multifactorial
Traits that depend on multiple genes combined w/ environmental influences; Ex: skin, heart disease, cancer, and alcholism
Which two tests do geneticists perform to determine which loci are responsible for human characters?
Pedigrees and association studies
Homozygous
Having two identical alleles for a given gene
Heterozygous
Having two different alleles for a given gene
Dominant
An allele that is fully expressed in the phenotype of a heterozygote
Recessive
An allele whose phenotypic effect is observed in a heterozygotes
Monohybrid cross
A cross between two organisms that are heterozygous for a character (or the self pollination of a heterozygous plant)
Dihybrid cross
A cross between two organisms that are each heterozygous for both of the characters being followed (or the self pollination of a plant that is heterozygous for both characters)
Qualitative character
A heritable feature that varies in an either or fashion
Quantitative character
A heritable feature that varies continuously over a range rather than in an either or fashion
Polygenic inheritance
An additive effect of two or more genes on a single phenotypic character
Pedigree
A family tree that describes the inheritance of a trait across generations
Association study
Data to correlate genotypes and phenotypes across many many individuals
What is the phenotypic ratio for the F2 generation when it is incomplete dominance?
1:2:1
