Genes, Chromosomes and Heredity Flashcards
Define clone
an organism or cell, or group of organisms or cells, produced asexually from one ancestor or stock, to which they are genetically identical
Define homologous chromosomes
chromosomes that synapse or pair during meiosis and that are identical with respect to their genetic loci and centromere placement
Define dihybrid cross
a genetic cross involving two characters in which the parents possess different forms of each character (e.g. yellow, round X green, wrinkled peas)
Define missense mutation
a point mutation in which a single nucleotide change results in a codon that codes for a different amino acid
Define complementary gene action
one of two or more genes that when present together produce effects qualitatively distinct from the separate effect of any one of them.
Define null mutation
A mutation (a change) in a gene that leads to its not being transcribed into RNA and/or translated into a functional protein product
___________ are the source of genetic variation, the raw material of evolution. They are needed for species to adapt
Mutations
Define molecular genetics
the field of biology that studies the structure and function of genes at a molecular level and thus employs methods of both molecular biology and genetics
What is the term used to describe when there is multiple allels equavalent to wild type?
Polymorphic
What is typical of a pedigree displaying an autosomal recessive trait?
- Males and females equally affected
- Skips generations
What does a mutation in the splice site do?
pre-mRNA may not be spliced correctly- could have a similar result to a frameshift mutation
True or False:
Complementary gene action is a type of epistasis
True
Define suppressor gene
a gene that suppresses the phenotypic expression of another gene
Define homozygote
an individual with identical alleles for a gene or genes of interest. These individuals will produce identical gametes (with respect to the gene or genes in questions) and will therefore breed true
Define penetrance
the frequency, expressed as a percentage, with which individuals of a given genotype manifest at least some degree of a specific mutant phenotype associated with a trait
What is the term used to describe when there is one wild type allele and the rest is mutant?
Monomorphic
Define codominance
condition in which the phenotypic effect of a gene’s alleles are fully and simultaneously expressed in the heterozygote
Define reciprocal cross
a pair of crosses in which the genotypes of the female is present as the genotype of the male in the other, and vice versa
Define dominant epistasis
when the dominant allele of one gene masks the effects of either allele of the second gene
Duchenne muscular dystrophy is an X-linked recessive disorder.
- If a woman who is a carrier of the disease gene has a normal partner what is the probability of having an affected child?
Define autosomal
a gene located on a numbered chromosome and usually. affects males and females in the same way
Define mutagen
an agent, such as radiation or a chemical substance, which causes genetic mutation
True or False:
Suppressor alleles are always dominant
False
They can be dominant or recessive
A ratio of 13:3 is typical of which type of gene interaction?
Recessive suppression
Define pedigree
in human genetics, a diagram showing the ancestral relationships and transmission of genetic traits over several generations in a family
What is typical of a pedigree displaying an autosomal dominant trait?
- Males and females equally affected
- Affected individuals in multiple generations
- Transmission by both sexes to both sexes
Define testcross
a cross between an individual whose genotype at one or more loci may be unknown and an individual who is homozygous recessive for the gene or genes in question
What type of inheritance does this pedigree show?
Sex influenced
Define incomplete penetrance
A form of penetrance in which not all individuals carrying a deleterious gene express the associated trait or condition
What is it called when an individual only has one copy of a gene?
Hemizygous
Define transmission genetics
the field of genetics concerned with heredity and the mechanics by which genes are transferred from parent to offspring
Define population genetics
the branch of genetics concerned with the hereditary makeup of populations
Define Mendel’s Law of Independent Assortment
Mendel’s second law that states that alleles for separate traits are passed independently of one another i.e from parents to offspring
Define allele
one of the possible alternative forms of a gene, often distinguished from other alleles by phenotypic effects
Define recessive
an allele whose potential phenotypic expression is overridden in the heterozygous condition by a dominant allele
Duchenne muscular dystrophy is an X-linked recessive disorder.
- What is the probabilty that a woman whose mother’s brother had the disease will have received the disease allele?
What type of inheritance does this pedigree show?
Autosomal recessive
What type of inheritance does this pedigree display?
X-linked recessive
Define monohybrid cross
a genetic cross involving only one character (e.g. AA X aa)
Define phenotype
the overt appearance of a genetically controlled trait
A certain type of flower can be purple (dominant) or white (recessive). You find a purple flower and want to determine what it’s genotype is.
a) What test do you perform?
b) What flower would you cross it with?
c) What do you expect if the genotype is PP?
d) What do you expect if the genotype is Pp?
a) Test cross
b) White flower
c) All purple flowers
d) 1:1 ratio (purple:white)
When organisms homozygous for mutations that show the same phenotype but are in different genes are crossed together, then the progeny are wild type. The mutations __________ one another
Complement
Cystic fibrosis is an autosomal recessive disorder. Two heterozygous parents are expecting a baby.
- What is the probability that the baby is a homozygote?
CC or cc
1/4 + 1/4 = 1/2
What sort of gene interaction does a ratio of 9:3:4 indicate?
Recessive epistasis
Define carrier
an individual heterozygous for a recessive trait
Is loss-of-function mutations usually dominant or recessive?
Recessive
Define loss-of-function
A mutation that results in reduced or abolished protein function
What is typical of a pedigree displaying an X-linked recessive trait?
- Males usually mostly affected
- Transmitted through unaffected females (carriers)
- No male to male transmission
Cystic fibrosis is an autosomal recessive disorder. Two heterozygous parents are expecting a baby.
- What is the probability that the baby is affected?
Cystic fibrosis is an autosomal recessive disorder. Two heterozygous parents are expecting a baby.
- What is the probability that they have a baby that is affected and then have a second baby who is unaffected?
Which trait in this monohybrid cross is dominant and which is recessive?
Round = dominant
Wrinkled = recessive
If we have two mutations with the same phenotype, we can test if they are affecting the same gene, or different genes using a _____________
Complementation test
Define splice site
the specific site at which splicing takes place during the processing of precursor messenger RNA into mature messenger RNA
Define conditional mutation
a mutation that has wild-type (or less severe) phenotype under certain “permissive” environmental conditions and a mutant phenotype under certain “restrictive” conditions
What type of inheritance is suspected when an allele appears to be dominant in one sex and recessive in another?
Sex-influenced
An allele of one gene that reverses the effect of a mutation of another gene, resulting in a wild-type phenotype is called what?
Suppressor allele
Define duplicate recessive epistasis
When recessive alleles at either of the two loci can mask the expression of dominant alleles at the two loci
What ratio is expected when two genes affect different traits?
9:3:3:1
Define overdominance
the phenomenon in which heterozygotes have a phenotype that is more extreme than either homozygous genotype
Define reverse mutation
a mutation that restores the ability of the gene to produce a functional protein
Define gynandromorph
an abnormal individual, especially an insect, having some male and some female characteristics
Define forward mutation
A mutation that changes a functional or wild type gene or allele to a nonfunctional or mutant gene or allele
Define monomorphic
having only one form
Define hemizygous
having a gene present in a single dose in an otherwise diploid cell. Usually applied to genes on the X chromosome in heterogametic males
Define haploinsufficiency
a condition that arises when the normal phenotype requires the protein product of both alleles, and reduction of 50% of gene function results in an abnormal phenotype
What are two environmental factors that can affect the phnotypic expression of a genotype?
Tempreature
Chemicals
Is spontaneous mutation random or adaptive?
Random
What type of gene interaction does this diagram show?
Complementary gene action
What type of gene interaction occurs in the Bombay blood group phenotype?
Recessive epistasis
Why do X-linked dominant conditions affect females less than males?
X-inactivation
When there is a ration that seemingly deviates from Mendalian ratios what is suspected?
Lethal alleles
Why does this diagram demonstrate suppression and not epistasis?
A suppressor cancels the expression of a mutant allele and restores the corresponding wild-type phenotype
Define pleiotropic
condition in which a single mutation causes multiple phenotypic effects
What is complementary gene action also called?
Duplicate recessive epistasis
Define incomplete dominance
expressing a heterozygous phenotype that is distinct from the phenotype of either homozygous parent
What are the three broad fields of genetics?
Transmission genetics Molecular genetics Population genetics
Define sex-influenced traits
phenotypic expression conditioned by the sex of the individual. A heterozygote may express one phenotype in one sex and an alternative phenotype in the other sex (e.g. pattern baldness in humans)
Define sex-limited traits
a trait that is expressed in only one sex een though the trait may not be X-linked or Y-linked
Are gain-of-function mutations usually dominant or recessive?
Dominant
Define spontaneous mutation
A mutation that arises naturally and not as a result of exposure to mutagens
Define heterozygote
an individual with different alleles at one or more loci. Such individuals will produce unlike gamtes and therefore will not breed true
Define heterogametic sex
the sex that produces gamete containing unlike sex chromosomes. In mammals, the male is the heterogametic sex
Define wild type
the most commonly observed phenotype or genotype, designated as the norm or standard
Define complementation test
a genetic test to determine whether two mutations occur within the same gene (cistron). If two mutations are introduced into a cell simultaneously and produce a wild-type phenotype (i.e. they complement each other), they are often nonallelic. If a mutant phenotype is produced, the mutations are non-complementing and are often allelic
When does a double homozygous mutant produce a novel phenotype?
When genes act in parallel pathways that contribute to a phenotype
Define nonsense mutation
a mutation in which a sense codon that corresponds to one of the twenty amino acids specified by the genetic code is changed to a chain-terminating codon
Define lethal gene
a gene whose expression results in premature death of the organism at some stage of its life cycle
Define genetically heterogenous
mutations at two or more genetic loci that produce the same or similar phenotypes
Define X-inactivation
a process by which one of the copies of the X chromosome present in female mammals is inactivated. The inactive X chromosome is silenced by it being packaged in such a way that it has a transcriptionally inactive structure called heterochromatin
Define trinucleotide repeat expansion
the DNA mutation responsible for causing any type of disorder categorized as a trinucleotide repeat disorder
What type of inheritance is this pedigree showing?
Autosomal recessive
This pedigree demonstrates what?
Gene complementation
Define hypomorphic mutation
A type of mutation in which the altered gene product possesses a reduced level of activity, or in which the wild-type gene product is expressed at a reduced level
A ratio of 9:7 is typical of what type of gene interaction?
Complementary gene action
What type of gene interaction occurs in labrador coat colours?
Recessive epistasis
Define homogametic sex
the sex that produces gametes with identical sex chromosome content; in mammals, the female is homogametic
What were the three early theories of inheritance?
Pangenesis Homunculus Blending theory
What does the type of dominance depend on?
- The proteins encoded by the genes and their function within the cell
- The effect of the mutant allele on protein function
- Which trait is being studied
Define chromosome theory of inheritance
the idea put forward independently by Walter Sutton and Theodor Boveri that chromosomes are the carriers of genes and the basis for the Mendelian mechanism of segregation and independent assortment
Define progenitor
a person or thing from which a person, animal, or plant is descended or originates; an ancestor or parent
Define non-coding region
components of an organism’s DNA that do not encode protein sequences. Some noncoding DNA is transcribed into functional non-coding RNA molecules (e.g. transfer RNA, ribosomal RNA, and regulatory RNAs)
A ratio of 15:1 indicates which type of gene interaction?
Duplicate genes
Define promoter
a region of DNA that initiates transcription of a particular gene. Promotersare located near the transcription start sites of genes, on the same strand and upstream on the DNA (towards the 5’ region of the sense strand)
Where in the body must a mutation occur for in to be inherited by the next generation?
Germ cell
Define duplicate genes
Two identical genes showing the same phenotypic action but localized in different regions of a chromosome or on different chromosomes
Define epistasis
the interaction of genes that are not alleles, in particular the suppression of the effect of one such gene by another
What type of cross is used to determine whether a trait is sex-linked?
Reciprocal cross
A ratio of 12:3:1 indicates which type of gene interaction?
Dominant epistasis
What is typical of a pedigree displaying an X-linked dominant trait?
- Both sexes affected but often excess of females
- Females less severly affected than males
- Affected males can transmit to daughters but not sons
What did Beadle and Tatum determine with the experiments with auxotrophs?
That genes encode proteins
What type of inheritance is this pedigree showing?
Autosomal dominant
Define true-breeds
a kind of breeding wherein the parents would produce offspring that would carry the same phenotype
True or False:
A recessive epistatic allele blocks or masks phenotypic effects of alleles of other genes only when it is heterozygous
False
Only when it is homozygous
Define genotype
the allelic or genetic constitution of an organism; often, the allelic composition of one or a limited number of genes under investigation
Based on this table, which enzyme does arg-1, arg-2 and arg-3 encode for?
Arg-1: Enzyme X
Arg-2: Enzyme Y
Arg-3: Enzyme Z
Define complete dominance
a form of dominance in heterozygous condition wherein the allele that is regarded as dominant completely masks the effect of the allele that is recessive
What are the types of dominant loss-of-function mutations?
Haploinsufficiency
Dominant-negative
Why do we use model organisms to study genetics?
Reproduce quickly Cheap Next to no ethics Lots of progeny Breed in the lab
Define gain-of-function mutation
A type of mutation in which the altered gene product possesses a new molecular function or a new pattern of gene expression. Gain-of-function mutations are almost always Dominant
Define Mendel’s Law of Segregation
Mendel’s first law that states that every individual organism contains two alleles for each trait, and that these alleles segregate (separate) during meiosis such that each gamete contains only one of the alleles
Define expressivity
the degree to which a phenotype for a given trait is expressed
Who discovered sex-linked inheritance?
Thomas Hunt Morgan
Define Blending theory
an obsolete theory in biology from the 19th century. The theory is that the progeny inherits any characteristic as the average of the parents’ values of that characteristic
Define dominant
the expression of a trait in the heterozygous condition
True or False:
Suppressor alleles may or may not have their own phenotype
True
Why did Mendel succeed in discovering autosomal inheritance?
- Good model organism
- Simple trait
- Repetition
- Developed and tested hypotheses
What does a mutation in the promoter or regulatory elements do?
Increase or decrease transcription of that gene
Define polymorphic
the existence of two or more discontinuous, segregating phenotypes in a population
Define pangenesis
a disproven hypothetical mechanism of heredity in which the cells throw off particles that collect in the reproductive products or in buds so that the egg or bud contains particles from all parts of the parent
What type of gene interaction does this diagram demonstrate?
Recessive epistasis
What does a mutation in the 5’ or 3’ UTR do?
Alters the ability of mRNA to be translated or mRNA stability
What is the common features of the F1 and F2 generations in a monohybrid cross?
F1: All dominant phenotype
F2: 3:1 ration of dominant to recessive phenotype
Define selective advantage
The characteristic of an organism that enables it to survive and reproduce better than other organisms in a population in a given environment
Define recessive epistasis
when the recessive allele of one gene masks the effects of either allele of the second gene
Duchenne muscular dystrophy is an X-linked recessive disorder.
- If a woman who is a carrier of the disease gene has a normal partner what is the probability of two of their children being affected?
Probability of one affected child is 1/4
Probability of 2: 1/4 x 1/4 = 1/16
When organisms homozygous for mutations that show the same phenotype but are in the same gene are crossed together, then the progeny are mutant. The mutations __________ one another
Fail to complement
What type of inheritance is this pedigree showing?
Autosomal dominant
Define sex-linked
A gene located in the sex chromosome
Define dominant negative
a type of dominant loss-of-function where the mutant protein is non-functional and interferes with the function of normal protein in heterozygotes
Define lethal mutation
A type of mutation in which the effect(s) can result in the death or reduce significantly the expected longevity of an organism carrying the mutation
Define heterozygote advantage
the case in which the heterozygous genotype has a higher relative fitness than either the homozygous dominant or homozygous recessive genotype
Define model organisms
an experimental organism conductive to research whose genetics is intensively studied on the premise that the findings can be applied to other organisms; for example, the fruit fly (Drosophila melanogaster) and the mouse (Mus musculus) are model organisms used to study the causes and development of human genetic diseases
Define coding region
portion of a gene’s DNA or RNA that codes for protein. The region usually begins at the 5’ end by a start codon and ends at the 3’ end with a stop codon. The sum total of the coding regions of an organism’s genome is called an its exome
Define mutation
the process that produces an alteration in DNA or chromosome structure; in genes, the source of new alleles
Define genetics
the branch of biology concerned with study of inherited variation. More specifically, the study of the origin, transmission, and expression of genetic information
