Genetics Flashcards
Character
Detectable inheritable feature (flower color, eye color)
Trait
variant of a character
True breed
All offspring with the same trait as parents (ie: Homozygous parent)
Hybridization
Mating of two contrasting true-breeding varieties
P generation
True-breeding parents
F2 generation
Results of when F1 individuals self/cross-pollinate with other F1 individual
F1 generation
hybrid offspring of P generation
Mendels Model
1)Alternative version of genes are responsible for variation in inherited characters
- alleles:
alternative (different) version of a gene
account for different traits(purple/white) observed for the same the character
2)For each character, organism receives 2 alleles: one from each parent: can be identical or different
3)If two alleles differ:
Dominant allele is fully expressed & will determine appearance; represented with capital letters
Recessive allele has no noticeable effects ; represented with lower case letters
Mendel: F1 = purple (allele is dominant)
4) Law of segregation: Alles seperate (segregate) during gamete formation
- egg/sperm receives only 1 one 2 alleles
- paired condition is restored by fusion of gametes (fertilization -> diploid zygote with 2 alleles)
- accounts for 3:1 ratio observed in F2 generation
- derived by following the inheritance of one character
Homozygous
Having 2 identical alleles for a gene
True breeding
Heterozygous
Having 2 different alleles for a gene
Not true breeding
Heterozygote is carrier of recessive trait
Phenotype
Physical expression of a gene (appearance) -> purple/white flower
Genotype
Genetic make up (PP or Pp = purple)
Punnet Square
Shows possible combination of sperm and egg
Predicts the results of genetic cross between individuals of known genotype
Test cross
Purpose:
- to determine if an organism with a dominant trait is either homozygous dominant or heterezygous
Procedure:
- cross “mystery” individual with a homozygous recessive individual (Pp/PP x pp)
Result:
if any of the offspring displays recessive phenotype, then mystery parent must be heterozygous
Monohybrids
individuals that are heterozygous for one character (ex: F1)
Monohybrid cross
cross between parents in which only one specific pair of alleles and therefore one specific trait is considered (F1 x F1)
Law of independent assortment
- derived by following the inheritance of 2 character
- F1 = dihybrids
Dihybrids
individual that are heterozygous for 2 characters
Dihybrid cross
- cross between parents in which 2 pairs of alleles and therefore 2 specific traits are considered (F1 x F1)
- used to determine if two characters are transmitted to offspring in a package or independently
Dihybrid cross experiment
Peas: i) R = round/ r=wrinkled ii) Y=yellow / y= green P generation : YYRR x yyrr (yellow & Round/green & wrinkled) F1 generation: YyRr Dihybrid cross: YyRr x YyRr Gametes: YR, Yr, yR, yr F2: Yellow/Round: Y_R_ (9/16) Yellow/Wrinkled: Y_rr (3/16) Green/Round: yyR_ (3/16) Green/Wrinkled: yyrr(1/16) Phenotypic ration: 9:3:3:1
conclusion of dihybrid cross experiment
- different genes separate independently of each other during gamete formation
- alleles inherited together do not necessarily get passed on together
- Note: genes near each other on the same chromosome tend to be inherited together
Non-mendalian genetic (occurence)
occurs when:
- gene has more than 2 alleles
- a gene produces multiple phenotypes
- alleles are not completely dominant or recessive
Incomplete dominance
heterozygote shows an intermediate phenotype
Codominance
full expression of both alleles in heterozygote Ex: AB blood group)
Groupe A
Genotype: I^a i or I^aI^a
Antigen: A
Antibody: Anti-B
Antigen
surface glycoprotein on red blood cell
Group B
Genotype: I^b i or I^bI^B
Antigen: B
Antibody: Anti-A
Group AB
Genotype: I^aI^b
Antigen: A & B
Antibody: none
universal recipient b/c no antibodies
Group O
Genotype: ii
Antigen: none
Antibody: Anti-A & Anti-B
universal donor b/c no antigen on RBC
Multiple alleles
Some genes may have more than 2 alleles (ABO blood group)
Epistatis
A gene at one locus altering the phenotypic expression of a gene at another locus E = color deposited e= no color deposited Ex: dog coat: 9:3:4 (Black: Brown: white)
Pleiotropy
single gene has multiple phenotypic effects (Ex: sickle cell anemia, cystic fibrosis has multiple symptoms
Polygenic inheritance
Additive effect of 2 or more genes leads to a single phenotype (Ex: Skin color)
Pedigrees
Family tree
Diagram of the relationship among parents & children
