PRINCIPLES OF HEREDITY / MENDELIAN LAWS Flashcards
DEFINE GENE
unit of heredity
DEFINE ALLELE
different forms of the same gene
DEFINE GENOTYPE
all genes in an organism
-genetic constitution
DEFINE PHENOTYPE
physical characteristics of genes
-influenced by environment
-result of genotype
DEFINE HOMOZYGOTE
same alleles
DEFINE HETEROZYGOTE
different alleles
DEFINE AUTOSOMAL
non sex chromosomes
DEFINE GONOSOMAL
sex chromosomes
WHAT IS THE P GENERATION?
–parental
-dominant homozygote X recessive homozygote
-AA x bb
WHAT IS THE F1 GENERATION?
– first filial generation, formed by the crossing of parental generation (AA x bb)
-descendent (children) are always heterozygotes (Ab)
WHAT IS THE MONOHYBRID F2 GENERATION?
-second filial generation, crossing of F1
(Ab x Ab)
-descendants have different genotypes (AA, Ab,
Ab, bb)
GENOTYPE = 1:2:1
PHENOTYPE = 3:1
WHAT IS A B1 BACKCROSS?
crossing parent with F1 (parent x F1) (AA x Aa)
-AA, AA, Aa, Aa → 1:1 (genotype) - same phenotype
WHAT IS A TEST CROSS?
- crossing an unknown genotypic individual with a known homozygous recessive (PP or Pp x pp)
- can be used to determine the genotype of the unknown parent
-Aa, Aa, aa, aa → 1:1 (genotype)
DEFINE MONOHYBRID
observation of 1 allele
DEFINE DIHYBRID
observation of 2 alleles
WHAT IS THE MEANING OF PHENOCOPY?
non-genetic, non-heritable, outer environment causes one genotype to look like another genotype
EG: woman dyes her hair from brown to black, looks like a different genotype, but her children will inherit brown hair
DEFINE PENETRATION
determines the probability that the allele will be expressed in the phenotype
WHAT IS THE IDENTITY OF RECIPRICAL CROSSES?
inheritance of autosomal genes is not dependent on sex
DEFINE DOMINANT RECESSIVE
dominant allele completely masks the expression of recessive allele
DEFINE CODOMINANCE
phenotype will express both alleles independent to each other (e.g. blood: allele A + allele B = blood type AB)
DEFINE INCOMPLETE DOMINANCE
–will express both phenotypes of both alleles, phenotype is an intermediate between the
dominant and recessive homozygotes (dominant blue + recessive red = purple flower)
NAME THE 3 LEVELS WHICH ALLELES CAN EFFECT
a) whole organisms - complete dominance, heterozygote looks like a homozygote
(round seed shape vs. wrinkled seed shape)
b) cell – incomplete dominance, we can distinguish individual cells
(low osmotic pressure vs. high osmotic pressure )
c) molecule - codominance, 50 % dominant and 50 % recessive allele
(functional enzyme vs. defective form of an enzyme)
WHO DOES MENDELS LAWS NOT APPLY TO?
does not apply to asexual or haploid organisms
WHAT IS MENDELS FIRST LAW?
Uniformity of F1 generation
-if you cross two homozygotes (AA x aa) → all individuals in F1 are equal (Aa)
WHAT IS MENDELS SECOND LAW?
Principle of segregation
-two alleles in one gene separate from each other into two gametes, each carrying one allele
-refers to F2
DOMINANT RECESSIVE
-phenotype: 3.1
-genotype: 1.2.1
INTERMEDIATE & CODOMINANCE
-phenotype: 1.2.1
-genotype: 1.2.1
WHAT IS MENDELS THIRD LAW?
Independent assortment
-alleles of two or more genes assort independently of one another
WHAT IS THE DIHYBRID F2 GENERATION?
P = AABB x aabb or AAbb x aaBB
F1 = in both cases: AaBb (all uniform)→ 4 times
F2 = AaBb x AaBb → Punnett square
GENOTYPES = genotypes: 9 different genotypes (1:2:1:2:4:2:1:2:1 → (1:2:1)^2 )
PHENOTYPES = 4 different phenotype (ratio 9:3:3:1 → (3:1)^2 )
WHAT IS AN ANALYTICAL BACKCROSS?
AaBb x aabb
-B1: 1:1:1:1
WHAT IS A POLYHYBRID CROSS?
more than 2 genes observed
-number of gametes = 2^n
-number of zygotes = 4^n
-genotype = (1:2:1)^n
-phenotype = (3:1)^n
NAME SOME DIFFERENCES FROM MENDELS LAW
lethality, decreased vitality
sex linked heredity
decreased penetrance
different expressivity
gene linkage
gene interactions
mitochondrial heredity
polygenic heredity
gene imprinting
dynamic mutations
structural balance chromosomal aberrations
WHAT DOES LETHALITY / DECREASED VITALITY MEAN?
not all genotypes have the same variability
COMPLETE RECESSIVE LETHALITY
-recessive and dominant homozygotes are lethal
-1AA : 2Aa:1aa (dead) or 1AA (dead) : 2Aa : aa
COMPLETE DOMINANT LETHALITY
-dominant homozygote and heterozygote are lethal
-caused by a mutation which is not passed onto next generation
-1AA (dead) : 2Aa (dead) : 1aa
DECREASED VITALITY RECESSIVE
-affect dominant or recessive homozygotes
-1AA : 2Aa : 1aa (sick) or 1AA (sick) : 2Aa : 1aa
DECREASED VITALITY DOMINANT
-affects dominant or recessive homozygote + heterozygote
-1AA : 2Aa (sick) :1aa (sick) or 1AA (sick): 2Aa (sick):1aa
WHAT IS MORGANS FIRST LAW?
genes are in a linear order on chromosomes
WHAT IS MORGANS SECOND LAW?
genes of a chromosome form a linkage group
-number of linkage groups is equal to the number of pairs of homologous chromosomes
WHAT IS MORGANS THIRD LAW?
Genes of homologous paired chromosomes can undergo crossing-over and gene exchange
-frequency of crossing over is directly proportional to the distance between genes (in centimorgans cM)
-distance of 1cM means 1% frequency of recombination during crossing over
HOW MANY GENES DETERMINE THE ABO BLOOD GROUP OF HUMANS?
1
WHERE CAN YOU FIND ANTIGENS AND ANTIBODIES?
antigens = surface of erythrocytes
antibodies = in plasma
-antigen produced from precursor polysaccharide and enzyme H adds another polysaccharide = H antigen (blood group O)
-from H antigen A and B antigens can be formed
WHAT IS THE FREQUENCY OF BLOOD GROUPS?
0 > A > B > AB
WHICH BLOOD GROUP IS THE UNIVERSAL DONOR?
O
WHICH BLOOD GROUP IS THE UNIVERSAL ACCEPTOR?
AB
WHY CANT ANTIGENS MIX WITH WITH THEIR ANTIBODY?
eg; A antigen and anti-A antibody
antigens are similar to bacterial saccharides to
which antibodies react, therefore they cannot mix
WHAT IS THE RHESUS FACTOR?
a certain type of protein found on the outside of blood cells
-genetically inherited from mother
-mainly influences antigen D
-dominant: Rh+ (83%)
-recessive: Rh- (17%)
Rh- can donate to Rh+ → Rh+ can accept Rh- and Rh+
Rh+ can not donate to Rh- → Rh- can only accept Rh-
problem during 2nd pregnancy:
-Rh- mother and Rh+ child
-body of mother from the 1st pregnancy has antibodies against Rh, which it now used against the child in the womb.
-antibodies in a pregnant woman’s blood destroy her baby’s blood cells
HOW MANY GAMETES DOES A TRIHYBRID CROSS FORM?
8
THE PRODUCT AND SUM RULE OF MENDELIAN GENETICS
