Genetics Exam 2

0.0(0) Reviews
Report Flashcard set

Spaced Repetition

Scientifically backed study method

spaced repetition


Review terms and definitions



Study with MC, T/F, and other questions


Practice Test

Take a test on your terms and definitions



103 Terms
😃 Not studied yet (103)
Alternate forms of the same gene
Wild type
-The allele that occurs most commonly in a population -May be dominant or recessive
mutant allele
-allele caused by a mutation in the wild-type allele -May specify an alternate gene product or inactivate the gene
null allele
•A gene that does not produce a functional gene product due to a mutation in the wild-type gene •Usually recessive
when the mutant allele is dominant
when naming alleles for model organisms, when is upper case used?
complete dominance
The heterozygote is phenotypically indistinguishable from the homozygote
incomplete dominance
Phenotype is intermediate between the two homozygous phenotypes
heterozygote advantage
-gives carriers with one affected allele benefit in another area -Helps explain why some mutations are maintained in a population
A single gene can present multiple effects
Heterozygote shows the phenotypic effects of both alleles equally
name for locus with multiple functional alleles
lethal alleles
•Mutations in essential genes •May be dominant or recessive
recessive lethal alleles
give 2:1 phenotypic ratio in monohybrid crosses
gene interactions
The situation in which more than one gene is involved in determining a particular phenotype
the effect of one gene pair masks or modifies the effect of another gene pair
•name for the gene that masks or modifies •may be dominant or recessive
The gene whose effects are masked or modified
recessive epistasis
-Two recessive alleles at the epistatic locus prevent expression of the alleles at the hypostatic locus -results in modified phenotypic ratio
dominant epistasis
•A dominant allele at the epistatic locus prevents expression of the alleles at the hypostatic locus
The presence of at least one dominant allele at each locus is necessary for wild-type phenotype
Homogametic sex
Produces gametes containing only one kind of sex chromosome
Heterogametic sex
Produces gametes which carry one of two different kinds of sex chromosomes
chromosomes with different in size and/or centromere position
Thomas Hunt Morgan
•Demonstrated that gene was located on the X chromosome •First data in support of the chromosome theory of heredity
sex linkage
Genes located on the sex chromosomes show different patterns of inheritance than autosomal genes
in x-linked recessive disorders which sex shows the trait more
a recessive trait is not sex linked
what does a mating involving an affected female in which some or all sons are not affected indicates
x linked dominant disorders
-Very rare -Affected males pass on condition to all of their daughters, but none of their sons
a dominant trait is not x linked
what does a mating involving an affected male in which some or all daughters are not affected indicate?
sex-limited heredity
•Phenotype is autosomally transmitted •Expressed in only one sex
Sex-influenced heredity
•Autosomally transmitted •Displayed in both males and females •Expression is dependent upon hormone constitution, so expression patters differ between males and females
variable expressivity
Individuals with the same genotype differ with respect to the severity of the phenotype
The probability that an individual who has the genotype associated with the trait will display the phenotype, affected interactions with the internal cellular environment and the external environment
how can genes be turned off in genomic imprinting
discontinuous traits
•characteristics with a small number of discrete phenotypes •Usually determined by one or a few gene loci
Having both genetic and environmental components
Bateson and Yule
who proposed the multiple factor/multiple gene hypothesis
Hermann Nilsson-Ehle
-performed experiments on grain color in wheat that were the basis for multiple factor hypothesis -proposed additive and nonadditive alleles
additive allele
Contributes a certain amount to the phenotype
nonadditive alleles
Does not contribute to the phenotype
Multiple-factor hypothesis
-Traits are polygenic -Many genes, each behaving in a Mendelian fashion, contribute towards the phenotype -Each gene locus may be occupied by either an additive or nonadditive allele -Together, the additive alleles produce substantial phenotypic variation
In the multiple factor hypothesis, the contribution of each additive allele to the final phenotype is approximately _____
continuous traits
Phenotypic variation can lie at any point within a set range of measurements
meristic traits
Traits in which the phenotype can be expressed as a whole number
Threshold Traits
-Typically have a small number of distinct phenotypic classes -The combination of alleles at multiple loci gives an individual a greater or lesser likelihood of showing one of these phenotypes
complementation analysis
used to determine whether two independently isolated mutations are due to mutations in the same or different genes
the mutations are in different genes
In complementation analysis 2 isolated mutants are crossed, what does wild type progeny indicate?
Bateson and Punnett
Who published the first study of linked genes about sweet pea plants inn 1906?
coupling between dominant and recessive alleles
What did bateson and punnett propose?
Thomas Hunt Morgan
Who hypothesized that parental (non-recombinant) types are more common than non-parental?
They are physically linked
What did Hunt Morgan propose about genes inherited together?
FA Janssens
Who first described chiasmata as the sites of crossing over in 1909?
What is the theoretical limitation to recombination with crossing over?
does crossing over always occur between genes?
recombinant frequency
An estimate of the proportion of chromosomes in which a crossover occurred between genes that is proportional to the distance between two linked genes
interchromosomal recombination
-recombination due to independent assortment -R.F. = 50%
Intrachromosomal recombination
-recombination due to crossing over - R.F. < 50%
The situation where gene pairs reside on the same chromosome
Linkage group
A group of genes having their loci on the same chromosome
the number of chromosomes
Number of linkage groups should be the same as what?
linkage phase
Combination of alleles linked on the same chromosome
coupling conformation
AB or ab
repulsion conformation
Ab or aB
if only paternal chromosome types are produced linkage is _____
Alfred Sturtevant
Used test cross data to map the relative distance between linked genes
The frequency of crossing over ______ as the distance between two genes increases
three point testcross
Aids in detection of double crossovers (DCOs) and allows relative order of genes on a chromosomes to be established with one cross
AaBbCc x aabbcc
what is crossed in an autosomal 3 point test cross?
AaBbCc female and abc/Y male
what is crossed in a sex-linked 3 point test cross?
What progeny type are most common?
What progeny type are least common?
in the middle
Where is the gene that is out of phase in the DCOs and NCOs located?
Add the 2 shorter distances together or add 2x the dcos to the formula.
How do you find the RF for the two most distant genes?
Microsatellites (STRs)
• Short sequences (1 to ~6 bp long) • Tandemly repeated • Found throughout the genome • E.g., CACACACA
in length
how do heterozygote microsatellite alelles differ?
Expansion repeat disorder
Disease occuring when the number of copies of a normally occurring STR increases to a critical number
Similar to microsatellites • Tandemly repeated sequence • Number of repeats varies, constituting different alleles • Repeat sequence is longer (10 to 100 nucleotides)
Single Nucleotide Polymorphisms
Variations at a single base pair
SNPs comprise over ____% of the 0.1% variation in the human genome
What kind of sex determination do humans use?
protenator mode
XX/X0 mode of chromosomal sex determination
lygaeus mode
XX/XY mode of chromosomal sex determination
A large portion of the Y chromosome is _______
Pseudoautosomal regions
-On both ends of the Y chromosome -Share homology with regions on both ends of the X chromosome
PARs allow for this to occur during prophase I of meiosis
Contains a number of genes specific for male development
-Sex-determining region Y -Encodes “testis determining factor”
Up to the _____ week of gestation, male and female embryos are identical
6 to 8
At ____ weeks, SRY becomes active
testes, female
If SRY is not transcribed • ____ do not develop • Embryo develops as a _____
Androgen Insensitivity Syndrome
• Reduce response of cells to testosterone and dihydrotesterone • Male sexual development is suppressed; individuals show phenotypes ranging from normal female external genitalia (CAIS) to normal male external genitalia with infertility
Mammalian females have ______ as many X-linked genes as males in the X-specific region of the X chromosome
Barr Body
- dosage compensation in mammals - all but 1 x chromosome is inactivated
Lyon Hypothesis
-Inactivation of X chromosome occurs early in development - Once inactivation occurs, all progeny cells have the same X chromosome inactivated - Leads to patches of tissues with different phenotypes
Anhidrotic ectodermal dysplasia
• Absence or hypoblastic development of several ectodermal organs including teeth, hair, nails and a variety of exocrine glands including sweat, salivary, and mammary glands • Heterozygous females (XAXa) are mosaics for these traits
What mode of sex determination do drosophilia use?
Calvin Bridges
• Studied the progeny of triploid female Drosophila • Concluded that the ratio of the number of X chromosomes to the number of haploid sets of autosomes determines sex
1X : 1 set of Autosomes
chromosome ratio that produces female fruit flies
ratios higher than 1:1
how are metafemales produced?
1X : 2 sets of Autosomes
chromosome ratio that produces male fruit flies
ratios lower than 1:2
how are metamales produced
ratios in between male and female
how is intersex produced in fruit flies
enivronmental sex determination
In some reptiles, including crocodiles, most turtles, and some lizards, sex is determined by the incubation temperature of the eggs during a critical period of embryonic development