Def Flashcards
What does trisomic refer to?
Having an extra chromosome in a specific pair (totaling three instead of the usual two)
For example, in humans, trisomy 21 causes Down syndrome.
Define polyploid.
Having more than two complete sets of chromosomes
Common in plants, like wheat, but rare in animals. Triploid organisms have three sets, while tetraploids have four.
What is aneuploid?
When the number of chromosomes is not an exact multiple of the haploid set
This includes conditions like trisomy and monosomy.
What does monosomic mean?
Having only one chromosome in a particular pair instead of the usual two
For example, Turner syndrome occurs in humans when there is only one X chromosome (45,X).
True or False: Polyploidy is common in animals but rare in plants.
False
Polyploidy is common in plants and rare in animals.
Fill in the blank: _______ refers to having an extra chromosome in a specific pair.
Trisomic
List the types of chromosomal variations.
- Trisomic
- Polyploid
- Aneuploid
- Monosomic
Fill in the blank: A polyploid organism has _______ or more complete sets of chromosomes.
more than two
What condition occurs in humans with only one X chromosome?
Turner syndrome
Fill in the blank: Aneuploid includes conditions like _______ and monosomy.
trisomy
True or False: Trisomy 21 is an example of monosomy.
False
Trisomy 21 is an example of trisomy, not monosomy.
What does p represent in the context of allele frequency?
Frequency of the dominant allele
Dominant alleles mask the effect of recessive alleles in heterozygous individuals.
What does q represent in the context of allele frequency?
Frequency of the recessive allele
Recessive alleles only manifest in homozygous recessive individuals.
What is the total of all allele frequencies in a population?
1 (100%)
This relationship is fundamental in population genetics.
What is the equation for genotype frequency?
p² + 2pq + q² = 1
This equation represents the proportions of different genotypes in a population.
What does p² represent in genotype frequency?
Frequency of the homozygous dominant genotype (e.g., AA)
Homozygous dominant individuals carry two dominant alleles.
What does 2pq represent in genotype frequency?
Frequency of the heterozygous genotype (e.g., Aa)
Heterozygous individuals have one dominant and one recessive allele.
What does q² represent in genotype frequency?
Frequency of the homozygous recessive genotype (e.g., aa)
Homozygous recessive individuals carry two recessive alleles.
How can the Hardy-Weinberg Equation be used to solve for allele frequencies?
By knowing the genotype frequencies or proportions of phenotypes
This allows for the calculation of p and q.
How can genotype frequencies be predicted using p and q?
By applying the Hardy-Weinberg Equation
Once p and q are known, expected genotype frequencies can be calculated.
What can phenotype frequencies be estimated from?
From genotype frequencies
This allows for the determination of the proportion of individuals expressing specific phenotypes.
What does a deviation from Hardy-Weinberg equilibrium indicate?
It may indicate evolutionary forces
Such forces include mutation, selection, and gene flow.
What does the 3:1 ratio represent in a monohybrid cross?
It describes the phenotypic outcome in the offspring of a monohybrid cross
Occurs when crossing two heterozygous individuals (Aa x Aa)
What are the genotypes produced in a monohybrid cross (Aa x Aa)?
1 homozygous dominant (AA), 2 heterozygous (Aa), 1 homozygous recessive (aa)
This results in a 1:2:1 genotype ratio
What phenotypic ratio is produced from a monohybrid cross?
3 dominant and 1 recessive
This results in a 3:1 phenotypic ratio
What does the 9:3:3:1 ratio represent in a dihybrid cross?
It describes the phenotypic outcome in the offspring of a dihybrid cross
Occurs when crossing two heterozygous individuals for both traits (AaBb x AaBb)
What phenotypes are produced in a dihybrid cross (AaBb x AaBb)?
9 with both dominant traits, 3 with the first trait dominant and the second recessive, 3 with the first trait recessive and the second dominant, 1 with both recessive traits
The specific ratios are 9:3:3:1
What does the 1:1 ratio represent?
It signifies an equal distribution of two phenotypes
Occurs when crossing a heterozygote with a homozygous recessive individual (Aa x aa)
What phenotypes are produced in a 1:1 ratio cross (Aa x aa)?
1 dominant and 1 recessive
The dominant phenotype comes from the heterozygote (Aa) and the recessive from the homozygous recessive (aa)
When does the 1:2:1 ratio occur?
In situations of codominance or incomplete dominance
Arises from a monohybrid cross of heterozygotes (Aa x Aa)
What are the phenotypes produced in a 1:2:1 ratio?
1 homozygous dominant, 2 heterozygotes with an intermediate phenotype, 1 homozygous recessive
Examples include red flowers (homozygous dominant), pink flowers (heterozygotes), and white flowers (homozygous recessive)
What does the 1:2:1 ratio reflect in genetic crosses?
It reflects the underlying mechanisms of segregation, independent assortment, and dominance
Particularly relevant in cases of codominance and incomplete dominance
What is the definition of autosomal dominant inheritance?
A trait or disorder is inherited in an autosomal dominant manner when one copy of the dominant allele is sufficient for the trait or disorder to be expressed.
What are the genotype possibilities for autosomal dominant traits?
- AA (homozygous dominant)
- Aa (heterozygous)
- aa (homozygous recessive) does not express the trait.
What is a key feature of autosomal dominant traits regarding affected individuals?
Affected individuals usually have at least one affected parent.
True or False: Autosomal dominant traits can skip generations.
False
In autosomal dominant inheritance, who is equally affected?
Both males and females.
Name two examples of autosomal dominant disorders.
- Huntington’s disease
- Marfan syndrome
How can you determine if an offspring will inherit an autosomal dominant trait?
If an offspring inherits at least one dominant allele from an affected parent.
What is the definition of autosomal recessive inheritance?
A trait or disorder is inherited in an autosomal recessive manner when two copies of the recessive allele are required for the trait or disorder to be expressed.
What are the genotype possibilities for autosomal recessive traits?
- aa (homozygous recessive) expresses the trait
- Aa (heterozygous carriers) do not express the trait
- AA (homozygous dominant) are unaffected.
What is a key feature of autosomal recessive traits regarding affected individuals?
Affected individuals often have unaffected carrier parents.
True or False: Autosomal recessive traits cannot skip generations.
False
In autosomal recessive inheritance, who is equally affected?
Both males and females.
Name two examples of autosomal recessive disorders.
- Cystic fibrosis
- Sickle cell anemia
How can you determine if an offspring will inherit an autosomal recessive trait?
Offspring must inherit one recessive allele from each parent to express the trait.
What is Y-Linked Inheritance?
Traits or disorders associated with genes on the Y chromosome, passed only from father to son.
Exclusively affects males.
What is a key feature of Y-Linked Inheritance?
All sons of an affected father will inherit the trait.
Examples include rare conditions like Y-linked infertility.
What is Mitochondrial Inheritance?
Traits or disorders caused by mutations in mitochondrial DNA, which is inherited exclusively from the mother.
Affects both males and females.
Who can pass on traits in Mitochondrial Inheritance?
Only mothers pass the trait to their offspring.
Examples include Leber’s hereditary optic neuropathy (LHON) and mitochondrial myopathy.
Fill in the blank: Y-Linked Inheritance affects only ______.
males
Fill in the blank: Mitochondrial Inheritance is inherited exclusively from the ______.
mother
What is the definition of Complete Dominance?
In this inheritance pattern, the dominant allele completely masks the effect of the recessive allele in heterozygous individuals.
This results in only two observable phenotypes: one for the dominant trait and one for the recessive trait.
What is the phenotypic ratio in a monohybrid cross for Complete Dominance?
3:1
This ratio occurs when two heterozygous individuals (Pp) are crossed.
Give an example of Complete Dominance.
Mendel’s pea plants, where purple flower color (P) is completely dominant over white (p).
This illustrates the masking effect of the dominant allele.
What is the definition of Incomplete Dominance?
In this pattern, the heterozygous genotype results in a phenotype that is a blend of the two alleles. Neither allele is completely dominant.
This leads to an intermediate phenotype.
What phenotypes are observable in Incomplete Dominance?
Three phenotypes: dominant, recessive, and intermediate (blended).
This occurs when alleles blend in the phenotype.
Provide an example of Incomplete Dominance.
Snapdragons, where red (RR) and white (rr) flowers cross to produce pink (Rr).
The pink flowers represent the intermediate phenotype.
What is the phenotypic ratio in a monohybrid cross for Incomplete Dominance?
1:2:1
This ratio occurs when two heterozygous individuals (Rr) are crossed.
What is the definition of Co-Dominance?
In this pattern, both alleles are expressed equally in the heterozygous genotype, resulting in a phenotype that shows features of both alleles simultaneously.
This leads to a distinct combined expression of both traits.
What phenotypes are observable in Co-Dominance?
Three phenotypes: dominant, recessive, and a combined expression of both traits.
This reflects the equal expression of both alleles.
Give an example of Co-Dominance.
Blood type AB, where alleles for A (I) and B (3) are co-dominant, resulting in both antigens being expressed.
This demonstrates the simultaneous expression of both alleles.
What is the phenotypic ratio in a monohybrid cross for Co-Dominance?
1:2:1
Similar to Incomplete Dominance, this ratio occurs in a co-dominance scenario.
What is the definition of Positive Assortative Mating?
Individuals are more likely to mate with those who share similar traits.
This includes traits such as height and education level.
Give an example of Positive Assortative Mating.
- Height: Taller individuals often pair with taller partners.
- Education: People with similar educational levels tend to form relationships.
These examples illustrate how similar traits influence mate selection.
What is a genetic impact of Positive Assortative Mating?
- Increases homozygosity.
- Reduces genetic variation for the selected traits.
Homozygosity refers to having similar alleles in the population.
What is the ecological or evolutionary relevance of Positive Assortative Mating?
It can contribute to reproductive isolation and speciation by favoring like-with-like pairings within subgroups.
This process can lead to the formation of new species over time.
What is the definition of Negative Assortative Mating?
Individuals are more likely to mate with those who have different or opposite traits.
This mating strategy contrasts with positive assortative mating.
Give an example of Negative Assortative Mating.
In humans, mate choices based on major histocompatibility complex (MHC) genes may favor partners with dissimilar immune system genes.
This promotes genetic diversity in immune responses.
What is a genetic impact of Negative Assortative Mating?
- Increases heterozygosity.
- May enhance survival and fitness by introducing diverse traits into the population.
Heterozygosity refers to having different alleles, which can improve adaptability.
What is pleiotropy?
A single gene influences multiple traits or phenotypes, often unrelated.
Examples include Marfan syndrome and sickle cell anemia.
Give an example of pleiotropy.
The Marfan syndrome gene affects connective tissue and results in features like tall stature, heart issues, and lens dislocation.
Another example is the gene for sickle cell anemia impacting hemoglobin and affecting blood circulation, resistance to malaria, and organ function.
Define epistasis.
The interaction between two or more genes, where one gene masks or modifies the effect of another.
Epistasis can be dominant or recessive.
What is dominant epistasis?
One dominant allele masks the expression of another gene.
An example is squash color.
What is recessive epistasis?
Two recessive alleles block the expression of another gene.
An example is Labrador coat color: black, brown, or yellow.
Provide an example of epistasis in mice.
In mice, coat color is controlled by two genes, and the pigment distribution gene may ‘override’ the pigment production gene.
What is X-inactivation (Lyonization)?
A process in female mammals where one of the two X chromosomes in each cell is randomly silenced to prevent overexpression of X-linked genes.
What is a consequence of X-inactivation?
Creates a ‘mosaic’ effect because different cells in the body may inactivate different X chromosomes.
Give an example of X-inactivation affecting phenotype.
Female calico cats have patches of orange and black fur due to X-inactivation affecting fur color genes.
Define co-dominance.
Both alleles in a heterozygous individual are fully and equally expressed, producing a phenotype that shows both traits simultaneously.
Provide an example of co-dominance.
Blood type AB, where both A and B antigens are equally expressed.
What is a mosaic in genetics?
An individual composed of cells with different genetic makeups, often due to mutations or chromosomal changes during early development.
Give examples of mosaicism.
- Skin conditions like mosaicism for pigmentation.
- Genetic disorders with variable expression, like Turner syndrome mosaics.
What is the Hardy-Weinberg equilibrium condition for a diploid locus with two alleles?
p + q = 1
In Hardy-Weinberg equilibrium, what does ‘p’ represent?
Frequency of the dominant allele
In Hardy-Weinberg equilibrium, what does ‘q’ represent?
Frequency of the recessive allele
What is the equation for the total number of genotypes at Hardy-Weinberg equilibrium?
D + H + R = N
How is the frequency of dominant homozygous genotypes denoted?
d
How is the frequency of heterozygous genotypes denoted?
h
How is the frequency of recessive genotypes denoted?
r
What is the equation for the total frequency of genotypes at Hardy-Weinberg equilibrium?
d + h + r = 1
How do you calculate the frequency of the dominant allele (p) using genotype numbers?
p = (2D + H) / 2N
How do you calculate the frequency of the recessive allele (q) using genotype numbers?
q = (2R + H) / 2N
How do you calculate the frequency of the dominant allele (p) using genotype frequencies?
p = (d + h) / 2
How do you calculate the frequency of the recessive allele (q) using genotype frequencies?
q = (r + h) / 2
What is the Hardy-Weinberg equation in terms of allele frequencies?
p² + 2pq + q² = 1
