Mendelian Genetics I and II Flashcards
week 3 and 4
allele
different genes located on same locus
what were the parameters of mendels pea experiment?
Traceable experiment system (controlled)
Looked for discrete, mutually exclusive traits.
What did the pea expeirment show?
dominance
How was dominance displayed?
Crossed: pure breeding, homozygous (P) talls with pure breeding shorts.
F1 = tall, F2 = 3:1 phenotype ration
Law of segregation
For any trait, pair of genes of each parents separate and are packaged into separate gametes = only one gene from each parent passes to offspring
locus
position gene occupies within a segment of a genome
co-dominance
both alleles fully expressed
incomplete domiance
Heterozygous phenotypically blend of homozygous dominant and homozygous recessive E.g red snap dragons
What is F1?
first generation offspirng from Parental generation (P)
What were the major conclusions of Mendels experiment?
Genes have multiple forms (alleles), T = tallness, t = shortness.
Each organism posses 2 genetic factors inherited from both parents
Gene may have one of two distinct types
One is dominant and determines the phenotype
Alleles separate with equal probability into gametes
What is the Chi-square test?
statistical test that determines whether the observed distribution of individual phenotypic categories is as predicted or occurs by chance.
Process for Chi-Square test:
1- record observed organisms in each phenotypic class = O
2- calculate expected values of each phenotypic class on basis of ratio = E
3- d (difference)= O-E
4= square d and divide by E in that phenotypic class.
What does a Chi-Square of O indicate?
no difference
What is the phenotypic ratio of a Dihybrid cross-breed
9: 3: 3: 1,
3:1 for single traits
What is the genotypic ratio for a Dihybrid cross-bredd?
: 1:2:1:2:4:2:1:2:1
What is Independent Assortment?
Random arrangement of homologous chromosomes pairs in metaphase I of Meiosis causing 2 different genes to randomly assort their alleles during gamete formation.
What is the exception to Mendle’s second law?
Some genes show linkage (inherited as single-unit from same chromosome).
How does meiotic recombination effect inheritance?
Alleles would otherwise always be inherited together.
Alleles on the same chromosome are partitioned into different gametes.
When will gene pairs assort independently? (2 ways)
- located on different chromosomes
- located far apart on the same chromosome
What is the probability of 2 genes crossing over proportional to?
Probability of 2 genes crossing over is proportional to: their distance apart on the chromosome
2 genes are linked if the show
Less than 50% recombinants relative to parental genotypes.
What is a test cross?
Dominant phenotype vs homozygous recessive organism = determine dominant parent genotype.
How is test cross completed?
Dihybrid cross with unknown dominant (home or hetero) and homozygous recessive.
If the result of the test cross shows: all offspring with dominant phenotype….
homozygous dominant genotype
If the result of the test cross shows: mix of dominant and receive in EQUAL proportions….
heterozygous genotype (no-linkage, 1:1:1:1 ration)
If the result of the test cross shows: mix of dominant and receive in UNEQUAL proportions….
heterozygous genotype, linkage (#parental haplotypes > # recombinant haplotypes)
What is Epiostasis?
Alleles in 1 gene mask phenotypic effects of another
Pleiotropy
1 gene may contribute to more than one visible characteristic
What is the general format for mutation nomenclature?
prefix–> position –> reference base –> new base
Allelles A and B are inhherited…
together
Alleles B and C are inherited…
equal chance of together or not
alleles a and b are inherited..
frequently, together
Alleles b and c are inherited…
equal chance of together or not
Assorted independently only if … why?
located on different chromosomes or far apart on the same chromosome
Because: The closer two genes are = the less likely cross-over will occur in meiosis.
What is a human example of Epistasis?
H Antigen and Bombay Phenotype
AB of ABO locus add different terminal sugars to RBCs
Hh = bloody type O REGARDLESS of alleles they carry at ABO
What does co-dominance, incomplete dominance and episatsis all have in common?
They are allelic combinations that do not exhibit standard dominant/recessive relationships.
What are the three different ways mutational events can lead to phenotypic biochemical changes?
Changes in coding region of a gene
Changes in non-coding region
Changes in regulator sequences
What is the result of a change in a coding region of a gene and an example?
Result: altered protein sequence, may not retain some function
e.g. cystic fibrosis
What is the result of changes in non-coding region and example?
Result: failure for correct splicing
e.g collagen disorder (osteogenesis imperfecta)
What is the result of changes in regulatory sequences and example?
Result: incorrect or failure of gene expression
e.g. deletion of b-globin Locus Control region (LCR) = B-thealassemia
What are the two proposed reasons for why some mutations are dominant and some are recessive?
Recessive mutations affect enzymes
Dominant mutations affect structural proteins
What are the four classes of gene mutations?
Base Subistitions
Deletions
Insertions
dynamic mutations
What are base-substitutions and what are the 3 types (and consewunces of these types)
SINGLE BASE change at replication of DNA repair
Synonymous (silent)
Missense (change amino acid structure)
Nonsense (change protein structure)
Dynamic mutations
Tandem repeats that change size following DNA replication
How are missense mutations denoted? and example.
by a three-letter abbreviation for wild-type amino acid, position number, three letter abbreviation for mutated amino acid
e.g Cys88Tyr
cystine at position 88, change into tyroisne
How are nonsense mutations denoted?
three-letter abbreviation for the wild type amino acid – position number – then a Ter or *, signifying the stop codon
e.g. Lys385Ter or Lys385*
How are insertion mutations named and example.
nucleotide number of the last wild type nucleotide before the insertion – ins
g.5384_5385insC
How are deletion mutations named?
nucleotide number of the first
deleted nucleotide - del (short for deletion)
g.6184del
What is a hybrid cross?
two separate genes considered = 9 different genotypic combinations
produces a dihybrid
Dihybrid vs monohybrid cross
monhybrid = AaxAa (3 possible genotypes)
Dihybrid cross= AaBb x AaBb (9 possible genotypes)
What stage of division is dihybrid crosses occurring and why?
Meiosis I
- 4 different chromosomes from diploid cell
What are the three steps of PCR amplification?
Denaturation= two strands of DsDNA separed as weak forces between helix are disrupted
annealing: binding primers to upstream and downsteam region that will be amplified
extenstion: Taq DNA polymerase adds dnTPs from 5-3 direction
How are an individual’s STR alleles analysed?
1- DNA estracted from individual
2- STRs amplifed
3- STRS tagged with a fluroescent makrers
4- capilary electrophrises (laser excites fluroesecnt dyes)
Describe the features of Autosomal dominant pedigrees.
Multiple generations are affected
male and female equally likely
affected person has one affected parent
Describe the features of autosomal recessive inheritance.
All offspring are carriers if a parent is affected
often skips generations
Describe X-linked recessive inheritance
Knight’s move
affects mostly males
never transmitted from father to son
Describe the features of X-linked dominant inheritance.
2:1 female: male
father to daughter
Crossing over
occurs in Prophase 1 and sees parental chromosomes swap genetic material. The probability of crossing over is proportional to the distance of genes apart.
Describe mitochondrial inheritance
only females can pass on disease
but male and female can develop
