Chapter 2 Flashcards
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
Define product rule
- the probability of 2 independent events both occurring is the product of their individual probabilities
Are gene transmissions in different generations independent or dependent events?
- independent
What principles do the 1:1, 3:1 and 1:2:1 ratios stem from?
-the principle of equal segregation
What types of genes are recessive mutations usually in?
- haplosufficient
Define gene discovery
- the process whereby geneticists find a set of genes affecting some biological process of interest by the single gene inheritance patterns of their mutant alleles or by genomic analysis
Define polymorphism
- the occurrence in a population of multiple forms of a trait or multiple alleles at a genetic locus
Define genetic dissection
- the use of recombination and mutation to piece together the various components of a given biological function
Define forward genetics
- the classical approach to genetic analysis, in which genes are first identified by mutant alleles and mutant phenotypes and later cloned and subjected to molecular analysis
Define reverse genetics
- an experimental procedure that begins with a cloned segment of DNA or a protein sequence and uses it (through directed mutagenesis) to introduce programmed mutations back into the genome to investigate function
Define character/trait
- an attribute of individual members of a species for which various heritable differences can be defined
Define pure lines
- a population of individuals all bearing the identical fully homozygous genotype
Define self
- to fetilize eggs with sperms from the same individual
Define parental generation (P)
- the two strains or individual organisms that constitute the start of a genetic breeding experiment; their progeny constitute the F1 generation
Define first filal (F1)
- produced by crossing 2 parental lines
- progeny of individuals arising from a cross of two homozygous diploid lines
Define second filal (F2)
- progeny produced by selfing or intercrossing the F1 generation
Define Medel’s first law
- law of equal segregation
- the production of equal numbers (50%) of each allele in the meiotic products (gametes) of a heterozygous meiocyte
Define monohybrid
- a single-locus heterozygote of the type A/a
Define monohybrid cross
- a cross between 2 individuals identically heterozygous at one gene pair
- ex A/a x A/a
Define meiocytes
- a cell in which meiosis takes place
- makes 4 gametes
Define tetrad
1) fours homologous chromatids in a bundle in the first meiotic prophase and metaphase
2) the four haploid product cells from a single meiosis
Define ascus
- in fungus, a sac that encloses a tetrad or an octad of ascospores
Define haploinsufficient
- describes a gene that, in a diploid cell, is insufficient to promote wild-type function in only one copy (dose)
Define haplosufficient
- describes a gene that, in a diploid cell, can promote wild-type function in only one copy (dose
Define homogametic sex
- the sex with homologous sex chromosomes
- typical females (XX)
Define heterogametic sex
- the sex that has heterogametic sex chromosomes (ex XY) and hence produces 2 different different kinds of gametes with respect to the sex chromosomes
Define dioecious species
- a plant species in which male and female organs are on separate plants
Define hemizygous gene
- a gene present in only one copy in a diploid organism
- ex and X-linked in gene in a male mammal
Define pseudoautosomal regions 1 and 2
- small regions at the ends of the X and Y sex chromosomes
- they are homologous and undergo pairing and crossing over at meiosis
Define pedigree analysis
- deducing single-gene inheritance of human phenotypes by a study of the progeny of matings within a family, often stretching back several generations
Define propositus
- in a human pedigree, the person who first came to the attention of the geneticists
Define morphs
- one form of a genetic polymorphism
- the morph can be either a phenotype or a molecular sequence
Define dimorphism
- a polymorphism with only 2 forms
Define dyad
- a pair of sister chromatids joined at the centromere, as in the first division of meiosis
Define bivalent
- 2 homologous chromosomes paired at meiosis
Define chromatids
- one of the two side-by-side replicas produced by chromosome division
Define SRY gene
- the maleness gene, residing on the Y chromosome
