Inheritance Flashcards
What is the means of inheritance?
Haploid gametes in parents fuse to form a diploid zygote
What is the method for conducting genetic crosses in flowering plants?
A pure-breeding, homozygous stock of parental plants is created via self-pollination (P-generation).
Parental plants with different characteristics are crossed to produce hybrid offspring (F1 generation).
F1 generation will produce an F2 generation with a variety of characteristics
What is an allele?
Different versions of the same gene
What is a genotype?
The combination of alleles inherited by an organism
What does homozygous and heterozygous mean?
Homozygous: having two identical alleles of a gene
Heterozygous: having two different alleles of a gene
What is a phenotype?
Observable traits of an organism resulting from genotype and environmental factors
How are dominant, recessive and codominant alleles expressed in a phenotype
Dominant:
Always expressed in the phenotype
Recessive:
Affects the phenotype if there is no dominant allele to mask it
Codominant:
Both alleles affect the phenotype when present
What is phenotypic plasticity?
An organism’s ability to express its phenotype differently depending on the environment, by varying patterns of gene expression
Not due to changes in genotype.
Changes in traits may be reversible.
What is an example of a human disease due to a recessive allele?
Phenylketonuria (PKU).
- Recessive genetic condition caused by mutation in an autosomal gene that codes for the enzyme needed to convert phenylalanine to tyrosine.
- Untreated => brain damage, mental retardation, serious medical problems
- Treated with a strict diet to restrict the intake of phenylalanine
Describe the existence of multiple alleles
- A person only inherits two alleles per gene, but there are typically multiple alleles for any gene within a gene pool.
- Single-nucleotide polymorphisms, a mutation to a single nucleotide base, can result in multiple phenotypic variants.
Give an example of
multiple alleles
ABO blood groups.
- Controlled by a single gene with multiple alleles
- A (I^A) and B (I^B) alleles are codominant; O (i) allele is recessive
What is the difference between incomplete dominance and codominance. Give an example to help differentiate them.
Codominance occurs when two characteristics are both expressed in the phenotype. E.g in ABO blood type in humans, blood type AB expresses both phenotypes.
Incomplete dominance occurs when the characteristics blend together. E.g crossing purebred four o’clock flowers of red and white => pink, an intermediate phenotype.
What determines sex in humans?
And which chromosome contains more gene for inheritance?
Sperm determines whether a zygote develops certain male-typical or female-typical physical characteristics
X chromosome => contains many more genes than the Y chromosome.
What is a sex-linked genetic disorder?
A genetic disorder caused by a gene controlling a characteristic located on a sex chromosome
What is an example of a sex-linked genetic disorder
Haemophilia, a genetic disorder wherby the body’s ability to control blood clotting is impaired
Is an X-linked recessive condition => occurs more frequentl in males as they are hemizygous
What is a pedigree chart? And what is it used for?
A chart of the genetic history of a family over several generations
Deduce patterns of inheritance of genetic disorders
What are monogenic traits?
Characteristics controlled by a single gene loci.
Tend to exhibit discrete variation: one of a number of distinct phenotypes are expressed
What are polygenic traits?
Characteristics controlled by more than two gene loci.
Tend to exhibit continuous variation: phenotype exists along a continuous spectrum of potential phenotypes
What is polygenic inheritance?
Inheritance of phenotypic characteristics that are determined by the collective effects of several different genes
What is discrete variaiton?
You either have a characteristic or not
What is continuous variation due to? Give an example
Polygenic inheritance and/or environmental factors.
Human skin colour:
- Polygenic trait => skin colour is controlled by multiple melanin producing genes
- Influenced by environment => affected by factors such as sun exposure
What is an autosomal condition?
Any genetic disorder caused by mutations to genes on any of the first 22 chromosomes
How you do determine if a value is an outlier (Box-and-whisker plot)
If it is more than 1.5 × IQR above the third quartile or below the first quartile.
What are linked genes?
Genes loci that are on the same chromosome
Are inherited together, but may become seperated due to recombination
What are unlinked genes?
Genes that are on seperate chromosomes
What is independent assorment? Why does it occur?
The allele inherited from one genes does not influence the allele inherited from a different gene
Bivalents line up with random orientations in metaphase I
What is Mendel’s second law?
- Law of independent assortment: unlinked genes segregate independently as a result of meiosis
When is the 9:3:3:1 ratio used? What is an exception to it
- Parents that are both heterozygous for both genes
- Linked genes
What can be deduced from a chi-squared test?
Whether genes are linked or unlinked.
x^2 > p = linked
x^2 < p= unlinked
