2B3 Advanced Concepts in Genetics Flashcards
Learn about complex genetics: codominance, incomplete dominance, and sex-linked traits.
What is dominance in genetics?
Refers to an inheritance pattern where one allele masks or hides the expression of another allele.
e.g. Brown eyes is dominant over blue eyes.
Define the ‘F1 generation’.
It is the first generation of offspring from a pair of controlled initial parents.
F1 generation is also called the first filial generation.
The controlled initial parents are known as the P generation.
What is meant by the term ‘heterozygous’ in genetics?
They have two different alleles for a trait, one dominant and one recessive.
e.g. Pp
What is meant by the term ‘homozygous’ in genetics?
They have two of the same alleles for a trait.
e.g. PP or pp
What is incomplete dominance?
Occurs when the heterozygous phenotype is a blend of the two parent phenotypes.
e.g. When a red-flowered plant (RR genotype) is crossed with a white-flowered plant (WW genotype), the offspring (RW genotype) have pink flowers.
This occurs because neither the red nor white allele is completely dominant, resulting in a blend of red and white pigments in the petals of the flowers.
Distinguish between incomplete dominance and codominance.
- Incomplete dominance results in a blend of traits.
- Codominance results in both traits being expressed simultaneously.
Which blood group in the diagram is ‘codominant’?
Blood group AB
Since the person with type AB blood produces both antigens, it is codominant, where both genes (A and B) are expressed.
What are polygenic traits?
Controlled by multiple genes located at different positions on chromosomes.
An example of a polygenic trait is human height. Multiple genes contribute to determining an individual’s height, making it a polygenic trait influenced by a combination of genetic factors.
Which blood group type is often described as the ‘universal donor’?
Type O
Individuals with type O blood are universal donors because their blood lacks A and B antigens.
Which blood group type is often described as the ‘universal recipient’?
Type AB
Individuals with type AB blood are universal recipients because they can accept A, B, AB, and O blood types.
Fill in the blank.
When there are three or more types of alleles for a given trait, these are called ___________ __________?
multiple alleles
Multiple alleles can result in a wide variety of traits within a population, contributing to the genetic diversity of the species as a whole.
Explain how the trait of human hair colour is an example of multiple alleles in action.
Multiple genes impact the color of a person’s hair.
One particular gene is the most important in determining whether they will have brown, blonde, or red hair.
What are the 3 alleles for the gene that codes for blood type?
- A
- B
- O
What are sex chromosomes?
The chromosomes that determine the sex of an organism.
What are autosomes?
The chromosomes in the genome that are not sex chromosomes.
What determines the sex of an individual in humans?
The combination of sex chromosomes inherited from both parents.
XY is male and XX is female.
Which parent determines the sex of the offspring in humans?
The father’s contribution determines the sex of the offspring, as fathers can pass on either an X or a Y chromosome.
What is a carrier in genetics?
An individual heterozygous for a recessive phenotype, meaning they have one dominant and one recessive allele for a trait.
What is a recessive allele?
An allele that can be masked by a dominant allele and only expresses its phenotype when in a homozygous state.
e.g. Blue eyes is recessive to brown eyes (which are dominant).
Is sickle cell anemia a dominant or recessive genetic disorder?
recessive disorder
This is caused by the presence of two recessive alleles, leading to sickle-shaped red blood cells.
How could you represent the alleles for sickle cell?
- ‘sca’ for the recessive allele
- ‘SCA’ for the dominant, normal allele
What does ‘SCA/sca’ genotype indicate in terms of sickle cell?
A carrier who does not exhibit the disease phenotype but can pass on the recessive allele.
Why do males have a higher chance of displaying recessive X-linked traits?
Males have only one X chromosome, so any recessive allele on it will be expressed since there’s no second X chromosome to mask it.
What is a sex-linked trait?
A phenotype produced by a recessive gene located on the X chromosome.
Give an example of a sex-linked trait.
Color blindness.
What does a Punnett square show in the context of sex determination?
The possible genotypes and phenotypes of offspring based on the combination of parental sex chromosomes.
What is a sex-limited trait and provide an example.
- A trait that is only expressed in one of the sexes, although the gene may be present in both.
- Example: premature baldness in males.
How do autosomal traits differ from sex-linked traits in terms of inheritance?
- Autosomal traits are inherited through non-sex chromosomes and typically have two alleles per gene.
- Sex-linked traits are inherited via the X chromosome and can be masked in females.
Why can sex-linked recessive trait be masked in females but not in males?
Females have two X chromosomes, so a dominant allele on one can mask a recessive allele on the other, while males have only one X chromosome.
What is the significance of the Y chromosome in sex determination?
It contains the SRY gene, which triggers male development.
In the context of color-blindness, an X-linked recessive disorder, why are males more frequently affected?
Because they only have one X chromosome, so a single recessive allele will express the trait.
Draw a punett square to show the possible genotypes of the offspring of a mother who is a carrier of colourblindness and an unaffected father.
The Punnett square shows that there is a chance of:
- 25% (Female, normal vision)
- 25% (Male, normal vision)
- 25% (Female, carrier)
- 25% (Male, colorblind)
In a certain species of cattle, the coat color can be red (RR), white (WW), or roan (RW).
If a roan bull (RW) is crossed with a white cow (WW), what are the possible genotypes and phenotypes of their offspring?
- Genotypes:
- RW (roan)
- WW (white)
- Phenotypes - Ratio: 1 roan : 1 white
Explain why only female mammals produce milk, even though both sexes carry the genes for milk production.
Because milk production is a sex-limited trait that is expressed only in females due to the influence of female hormones, particularly prolactin and oxytocin, which regulate milk production.
