Heredity Flashcards
Gregor Mendel
“Father of Modern Genetics”: monk who bred garden peas to study the patterns of inheritance
Mendel’s Approach to Inheritence
First, he studied traits that were clear-cut with no intermediates between varieties. second, he collected data from a large sample, with plants from several generations. Third, he applied statistical analysis.
Blended Inheritance
19th century belief that traits were passed in a mixture of fluids from parents to children and blended together
Particulate Inheritance
Mendel’s Theory: inherited characteristics are carried by discrete units, genes (he called them elements)
Probability: Multiplication Rule
To find the probability of two independent events happening, multiply the chance of one happening by the chance that the other will happen.
Probability: Addition Rule
When more that one arrangements of events producing the specific outcome is possible, the probabilities for each outcome are added together.
Law of Dominance
Mendel’s First Law: states that when two homozygous for two opposing traits are crosse, the offspring will by hybrid but will exhibit only the dominant trait and the trait that remains hidden is recessive
Law of Segregation
During the formation of gametes, the two traits carried by each parent separate.
Monohybrid Cross
(Tt)(Tt); the phenotype ratio from this cross is 3:1 (dominant to recessive); the genotype ratio is 1:2:1 (25% homozygous dominant: 50% heterozygous: 25% homozygous recessive)
Testcross: (B/b)(b/b)
Phenotype is 1:1 and genotype is also 1:1. Half will by heterozygous for this trait and half will be homozygous recessive.
Testcross: (B/B)(b/b)
Phenotype is 1 and genotype is also 1. All the offspring will be heterozygous for this trait.
Law of Independent Assortment
Applies when a cross is carried between two individuals for two or more traits that are not on the same chromosome.: Staes that during gamete formation the alleles of a gene for one trait segregate independently from the alleles for another trait. (REMEMBER: Meiosis I line up is random)
Dihybrid Cross
A cross between two F(1) plant because it is a cross between two individuals that are hybrid for two different traits.
Dihybrid Cross: Phenotype Ratio
9:3:3:1
Incomplete Dominance
Characterized by blending. Ex. a black animal mates with a white animal and produces grey babies.
Codominance
Both traits show. Ex. MN blood groups in humans, if you get M and N it’s not heterozygous both M and N are expressed.
Multiple Alelles & Blood Types
When there are more that two allelic forms of a gene. Ex. in humans there are 4 blood types determined by three alleles A, B and O. A and B are codominant and O is recessive.
Blood Type A
can be homozygous (AA) or hybrid (Ai)
Blood Type B
can be homozygous (BB) or hybrid (Bi)
Blood Type AB
codominance (AB)
Blood Type O
expressed as: ii
Pleiotropy
The ability of one single gene to affect and organisms in several ways.
Pleiotropy: Frizzle Trait
In chickens, the frizzle trait is a gene for a malformed feather. This mutation causes the development of feathers that cannot keep the animal warm and results in changes to several organ systems.
Pleiotropy: Siamese Cats
The same allele responsible for the body’s coloration is the same one responsible for the crossed eyes.
Marfan Syndrome
Pleiotropy in humans in which a single defective gene results on abnormalities of the eyes, skeleton, and the great blood vessels.
Epistasis
Two separate genes control one traits by one gene masks the expression of the other gene. The gene that masks the expression of the other gene is epistatic to the gene it masks.