Chapter 2 Flashcards
What are wild types and mutants?
Wild type- most common form of any property of an organism
Found “in the wild”
Wild type and it’s symbols aren’t used in human genetics because it’s impossible to define
Mutants- individual organisms having some abnormal form of property
Arise from heritable change in DNA of a gene called mutation
What are polymorphisms?
The coexistence of 2 or more reasonably common phenotypes of a biological property
Ex: occurrence of both red and orange fruits plants in a population of wild raspberries
What are the 4 steps of functional analysis by gene discovery?
- Amass mutants affecting the biological property of interest
- Cross (mate) the mutants to wild type to see if their descendants show ratios of wild to mutant that are characteristic of single gene inheritance
- Deduce the functions of the gene at the molecular level
- Deduce how the genes interacts with other genes to produce the property in question
What is parental generation, first filial generation, and second filial generation?
Parental generation (P)- parents
First filial generation (F1)- progeny from the cross between parents
Second filial generation (F2)- grown F1 selfed and made into F2
Page 35
Pages 38-39
What are the 7 explanations for pea colour Mendel used to birth the science of genetics into modern terms?
- A hereditary factor called a gene is needed for pea colour
- Each plant has a pair of this type of gene
- Gene comes in two forms called alleles (upper case Y and lower case y)
- Plant can either be Y/Y, Y/y, or y/y
- In Y/y plant, the Y allele dominates so phenotype will be that colour (yellow)
- In meiosis, members of gene lair separate equally into the cells that become eggs and sperm (gametes). Equal separation is known as Mendel’s first law (law of equal segregation)
- At fertilization, gametes fuse randomly, regardless of which of the alleles they bear
Define: Zygote Homozygote Heterozygote Monohybrid Homozygous dominant/recessive Heterozygous
Zygote- a fertilized egg, the first cell that develops into a progeny
Homozygote- pair of identical alleles (Y/Y)
Heterozygote- plant with two different alleles (Y/y)
Monohybrid- heterozygote for one gene
Homozygous dominant- YY
Homozygous recessive- yy
Heterozygous- Yy
Pages 38-39
What is mitosis vs meiosis?
Mitosis- somatic (body) cells divide to increase their number
Can happen in haploid or diploid cells but either way results in 2 parent cells
2n -> 2n + 2n or n -> n + n
Chromosomes all replicate to make 2 identical copies of itself (sister chromatids)
Meiosis- producing sex cells (gametes) through 2 cell divisions, 4 cells produced from one progenitor cell, meiosis only takes place in diploid cells, results in haploid cells
2n -> n + n + n + n
Overall halving of chromosomes
Page 40
Pages 42-43
Page 47
Slide 3, 5-27
What is a dyad?
What is a bivalent?
What is a tetrad?
Dyad- replicate sister chromatids
Bivalent- unit comprising pair of synapsed dyads
Tetrad- 4 chromatids that make up a bivalent
The four haploid cells that result from meiosis contain one member of a tetrad
Page 42
Slide 4, 8
What do mutations alter?
Most mutations that alter phenotype alter the amino acid sequence of the gene’s protein product, resulting in reduced or absent function
Genotype- organisms hereditary info
Phenotype- organisms observed properties
What is the molecular explanation for recessiveness?
(What is haplosufficient)
What is molecular explanation for dominance?
(What is haploinsufficient)
Recessiveness is observed in null mutations in genes that are functionally haplosufficient (one gene copy has enough function to produce a wild type phenotype)
A null mutant allele will be dominant in haploinsufficient genes because in a heterozygote (+/P), the single wild type allele cannot produce enough product for normal function
Page 50
What are the 3 simple cases that cover how we know if a mutant allele is dominant or recessive?
Standard procedure is to cross mutant with wild type (if mutant is sterile then another approach is needed)
- A fertile flower mutant with no pigment in the petals (ex: white petaled in contrast with normal red)- page 51
- A fertile fruit fly mutant with short wings- page 52
- A fertile mold mutant that produces excess hyphal branches (hyperbranching)- page 53
What is a testcross or tester?
The cross of an individual of unknown heterozygosity (for one gene or more) with a fully recessive parent
Ex: crossing A/? with a/a, if 1/2 A/a and 1/2 a/a results then the allele in question is a making it heterozygous, if all A/a results then the allele in question is A making it homozygous
What are sex chromosomes?
Humans have 46 chromosomes
22 pairs of autosomes and 2 sex chromosomes
Females= 44autosomes + XX
Makes= 44autosomes + XY
Females are homogametic sex because their gametes are only if one type since the 2 X chromosomes segregate in meiosis and each egg receives an X
Makes are heterogeneity sex since half the gametes get X and half get Y
Sex chromosomes carry genes in differential regions that show inheritance patterns called sex linked genes (makes have SRY that determines maleness)
Page 55
Slides 81-85
What are dioecious species?
Species showing animal-like sexual dimorphism, with female plants bearing flowers containing only ovaries and male plants bearing flowers containing only anthers
Some (not all) dioecious plants have a nonidentical pair of chromosomes associated with (most certainly determining) the sex of the plant
What is X linked inheritance?
Mutant alleles in the differential region of the X chromosome show a single gene inheritance pattern
Pages 56-57!!
What is Y linked inheritance?
Mutant alleles of the few genes in the differential region of the Y chromosome
Study the symbols and meanings of pedigree charts on page 59 textbook
Okay
How do inbreds run a higher risk of passing on recessive homozygous diseases than normal couples?
Because to get a recessive disease, the parents must both carry the gene from their ancestors and if both parents are same family then they most likely both have the same gene which will ultimately lead to homozygous recessive children or grandchildren
Autosomal recessive disorders are revealed by the appearance of the disorder in the male and female progeny of the unaffected parents
What is the difference between autosomal recessive diseases and autosomal dominant diseases?
Autosomal recessive disorders are revealed by the appearance of the disorder in the male and female progeny of the unaffected parents
Autosomal dominant disorders show affected males and females in each generation; they also show affected men and women transmitting the condition to equal proportions of their sons and daughters
What are morphs and dimorphism?
Morphs- alternate phenotypes of a polymorphism, they are often inherited as alleles of a single autosomal gene in the standard Mendelian matter
Dimorphism- 2 morphs, simplest polymorphisms (blue vs brown eyes, pigmented vs blond hair, widows peak vs none)
What are X-linked recessive disorders?
Many more males than females show the rare phenotype (female can only inherit the genotype if her mother and father have allele, male only needs 1)
None of the offspring of an affected male shows the phenotype, but all his daughters are carriers (heterozygous)
None of the sons of an affected male show the phenotype nor will they pass the condition on to their descendants (since sons inherit Y chromosome not X)
Pages 65-67
Slides 52-61
What are X-linked dominant disorders?
Affected males pass the condition to all their daughters but to none of their sons
Affected heterozygous females married to unaffected males pass the condition to half their sons and daughters
Slides 62-70
Study the breakdown of a pedigree case on page 69 textbook
Okay
What is the product rule in genetics?
The probability of 2 independent events both occurring is the product of their individual probabilities
EX: we can calculate that the probability of the husbands being a heterozygote is the probability of his fathers being a heterozygote (2/3) times the probability of his father having a heterozygote son (1/2), which is 2/3 x 1/2 = 1/3
