2B3 Advanced Concepts in Genetics

Question 1

What is dominance in genetics?

Answer 1

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.

Question 2

Define the ‘F1 generation’.

Answer 2

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.

Question 3

What is meant by the term ‘heterozygous’ in genetics?

Answer 3

They have two different alleles for a trait, one dominant and one recessive.

e.g. Pp

Question 4

What is meant by the term ‘homozygous’ in genetics?

Answer 4

They have two of the same alleles for a trait.

e.g. PP or pp

Question 5

What is incomplete dominance?

Answer 5

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.

Question 6

Distinguish between incomplete dominance and codominance.

Answer 6

• Incomplete dominance results in a blend of traits.
• Codominance results in both traits being expressed simultaneously.

Question 7

Which blood group in the diagram is ‘codominant’?

Answer 7

Blood group AB

Since the person with type AB blood produces both antigens, it is codominant, where both genes (A and B) are expressed.

Question 8

What are polygenic traits?

Answer 8

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.

Question 9

Which blood group type is often described as the ‘universal donor’?

Answer 9

Type O

Individuals with type O blood are universal donors because their blood lacks A and B antigens.

Question 10

Which blood group type is often described as the ‘universal recipient’?

Answer 10

Type AB

Individuals with type AB blood are universal recipients because they can accept A, B, AB, and O blood types.

Question 11

Fill in the blank.

When there are three or more types of alleles for a given trait, these are called ___________ __________?

Answer 11

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.

Question 12

Explain how the trait of human hair colour is an example of multiple alleles in action.

Answer 12

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.

Question 13

What are the 3 alleles for the gene that codes for blood type?

Answer 13

• A
• B
• O

Question 14

What are sex chromosomes?

Answer 14

The chromosomes that determine the sex of an organism.

Question 15

What are autosomes?

Answer 15

The chromosomes in the genome that are not sex chromosomes.

Question 16

What determines the sex of an individual in humans?

Answer 16

The combination of sex chromosomes inherited from both parents.

XY is male and XX is female.

Question 17

Which parent determines the sex of the offspring in humans?

Answer 17

The father’s contribution determines the sex of the offspring, as fathers can pass on either an X or a Y chromosome.

Question 18

What is a carrier in genetics?

Answer 18

An individual heterozygous for a recessive phenotype, meaning they have one dominant and one recessive allele for a trait.

Question 19

What is a recessive allele?

Answer 19

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).

Question 20

Is sickle cell anemia a dominant or recessive genetic disorder?

Answer 20

recessive disorder

This is caused by the presence of two recessive alleles, leading to sickle-shaped red blood cells.

Question 21

How could you represent the alleles for sickle cell?

Answer 21

• ‘sca’ for the recessive allele
• ‘SCA’ for the dominant, normal allele

Question 22

What does ‘SCA/sca’ genotype indicate in terms of sickle cell?

Answer 22

A carrier who does not exhibit the disease phenotype but can pass on the recessive allele.

Question 23

Why do males have a higher chance of displaying recessive X-linked traits?

Answer 23

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.

Question 24

What is a sex-linked trait?

Answer 24

A phenotype produced by a recessive gene located on the X chromosome.

Question 25

Give an example of a sex-linked trait.

Answer 25

Color blindness.

Question 26

What does a Punnett square show in the context of sex determination?

Answer 26

The possible genotypes and phenotypes of offspring based on the combination of parental sex chromosomes.

Question 27

What is a sex-limited trait and provide an example.

Answer 27

• A trait that is only expressed in one of the sexes, although the gene may be present in both.
• Example: premature baldness in males.

Question 28

How do autosomal traits differ from sex-linked traits in terms of inheritance?

Answer 28

• 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.

Question 29

Why can sex-linked recessive trait be masked in females but not in males?

Answer 29

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.

Question 30

What is the significance of the Y chromosome in sex determination?

Answer 30

It contains the SRY gene, which triggers male development.

Question 31

In the context of color-blindness, an X-linked recessive disorder, why are males more frequently affected?

Answer 31

Because they only have one X chromosome, so a single recessive allele will express the trait.

Question 32

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.

Answer 32

The Punnett square shows that there is a chance of:

• 25% (Female, normal vision)
• 25% (Male, normal vision)
• 25% (Female, carrier)
• 25% (Male, colorblind)

Question 33

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?

Answer 33

• Genotypes:
  • RW (roan)
  • WW (white)
• Phenotypes - Ratio: 1 roan : 1 white

Question 34

Explain why only female mammals produce milk, even though both sexes carry the genes for milk production.

Answer 34

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.