Define properties
- a characteristic feature of an organism
- ex: size, shape, colour, enzymatic activity
What are the general steps of functional analysis by gene discovery?
1) amass mutants affecting the biological property of interest
2) cross the mutants to wild type to see if their descendants show ratios of wild to mutant that are characteristic of single-gene inheritance
3) deduce the functions of the genes at the molecular level
4) deduce how the gene interacts with other genes to produce the property in question
How could you increase the mutation rate?
- exposing the organisms to radiation or chemicals
How could you test for single gene inheritance?
- cross a mutant and a wild-type and look at the ratios of F1 and F2
- aka do a test cross
What are the seven things Mendel learned from crossing pea plants?
1) a hereditary fact called a gene is necessary for producing pea colour
2) each plant has a pair of this type of gene
3) the gene comes in 2 forms called alleles (Y or y)
4) a plant can be either Y/Y, Y/y or y/y
5) in Y/y the Y allele is dominant and the y allele is recessive
6) in meiosis the members of a gene pair seperate equally into the gametes (Mendel’s first law), a single gamete contains one member of the gene pair
7) at fertilization, gametes fuse randomly regardless of which of the alleles they bear
What’s the number of genetic information at each major stage of meiosis?
Start- 2 homologs
Replication- 2 dyads
Pairing- tetrad
1st division- one dyad to each daughter cell
2nd division- one chromatid to each daughter cell
What are 2 reasons for using haploids as model organisms?
1) simple crosses, only single-gene inheritance patterns
2) all alleles are expressed in the phenotype because there’s no masking of recessives by dominant on the other homolog
What are alleles at the molecular level?
- identical for most of the sequence, but differ by 1 or several alleles
What are the protein-encoding regions?
- the exons
What area on the gene is very sensitive to mutation?
- the area encoding the genes active site
How can alleles be recessive?
- recessiveness is observed in null mutations in genes that are haplosuffient
How can the single-gene inheritance of sterile mutants be demonstrated?
- in a diploid organism a sterile recessive mutant can be propagate as a heterozygote and then the heterozygote can be selfed to produce the expected 25% homozygous recessive for study
- a sterile dominant mutant is a genetic dead end, cannot be propagated sexually but if its a plant of fungi can be propagated asexually
How could you find out if an unknown genotype showing the dominant phenotype is heterozygous or homozygous?
- do a testcross
- cross the organism with a known homozygous recessive individual (aka tester)
- if a plant or fungi can self it (if hetero will be 3:1)
What is a pattern in a pedigree that would reveal autosomal recessive inheritance?
1) the disorder appears in the progeny of unaffected parents
2) the affected progeny includes females and males
Why aren’t Mendelian ratios not typically seen in single family?
- because the sample size is too small
- therefore, any ratio is possible
Why do people in earlier and later generations tend not to have autosomal recessive disorders?
- it’s rare, so most people don’t have the allele
- people who do have the allele are typically carriers (heterozygous) because it’s much more likely to have 1 copy of a rare allele than 2
What does inbreeding increase the probability of occurring?
- 2 heterozygotes mating, making homozygous recessive progeny
What are the main clues used to identify an autosomal dominant disorder with Mendelian inheritance?
1) phenotypes tend to appear in every generation
2) affected mothers and fathers transmit the phenotype to both sons and daughters
T/F: polymorphism is popular in a natural population of plants and animals
- true
- lots of characteristics are polymorphic, even at a DNA level
What are 3 things that commonly occur with rare X-linked recessive disorders?
1) there’s more males than females with the rare phenotype (more males=more rare)
2) none of an affected male’s progeny show the phenotype, but all daughters are carriers (F2= half sons will show the phenotype)
3) none of the sons of an affected male show the phenotype, nor will they pass it on
What are 2 characteristics of X-linked dominant disorders?
1) affected males pass the condition to all their daughters but none of their sons
2) affected heterozygous females married to unaffected males pass the condition to half their daughters and sons
T/F: X-linked dominant disorders are common
- false, they aren’t
What’s a pattern seen with Y-linked inheritance?
- exclusive male to male transmission
- extremely rare
What can knowledge of transmission patterns in families help with?
- calculating the probability of prospective parent’s children having the disorder
