Inheritance

Question 1

What is the means of inheritance?

Answer 1

Haploid gametes in parents fuse to form a diploid zygote

Question 2

What is the method for conducting genetic crosses in flowering plants?

Answer 2

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

Question 3

What is an allele?

Answer 3

Different versions of the same gene

Question 4

What is a genotype?

Answer 4

The combination of alleles inherited by an organism

Question 5

What does homozygous and heterozygous mean?

Answer 5

Homozygous: having two identical alleles of a gene
Heterozygous: having two different alleles of a gene

Question 6

What is a phenotype?

Answer 6

Observable traits of an organism resulting from genotype and environmental factors

Question 7

How are dominant, recessive and codominant alleles expressed in a phenotype

Answer 7

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

Question 8

What is phenotypic plasticity?

Answer 8

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.

Question 9

What is an example of a human disease due to a recessive allele?

Answer 9

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

Question 10

Describe the existence of multiple alleles

Answer 10

• 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.

Question 11

Give an example of
multiple alleles

Answer 11

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

Question 12

What is the difference between incomplete dominance and codominance. Give an example to help differentiate them.

Answer 12

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.

Question 13

What determines sex in humans?
And which chromosome contains more gene for inheritance?

Answer 13

Sperm determines whether a zygote develops certain male-typical or female-typical physical characteristics
X chromosome => contains many more genes than the Y chromosome.

Question 14

What is a sex-linked genetic disorder?

Answer 14

A genetic disorder caused by a gene controlling a characteristic located on a sex chromosome

Question 15

What is an example of a sex-linked genetic disorder

Answer 15

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

Question 16

What is a pedigree chart? And what is it used for?

Answer 16

A chart of the genetic history of a family over several generations
Deduce patterns of inheritance of genetic disorders

Question 17

What are monogenic traits?

Answer 17

Characteristics controlled by a single gene loci.
Tend to exhibit discrete variation: one of a number of distinct phenotypes are expressed

Question 18

What are polygenic traits?

Answer 18

Characteristics controlled by more than two gene loci.
Tend to exhibit continuous variation: phenotype exists along a continuous spectrum of potential phenotypes

Question 19

What is polygenic inheritance?

Answer 19

Inheritance of phenotypic characteristics that are determined by the collective effects of several different genes

Question 20

What is discrete variaiton?

Answer 20

You either have a characteristic or not

Question 21

What is continuous variation due to? Give an example

Answer 21

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

Question 22

What is an autosomal condition?

Answer 22

Any genetic disorder caused by mutations to genes on any of the first 22 chromosomes

Question 23

How you do determine if a value is an outlier (Box-and-whisker plot)

Answer 23

If it is more than 1.5 × IQR above the third quartile or below the first quartile.

Question 24

What are linked genes?

Answer 24

Genes loci that are on the same chromosome
Are inherited together, but may become seperated due to recombination

Question 25

What are unlinked genes?

Answer 25

Genes that are on seperate chromosomes

Question 26

What is independent assorment? Why does it occur?

Answer 26

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

Question 27

What is Mendel’s second law?

Answer 27

• Law of independent assortment: unlinked genes segregate independently as a result of meiosis

Question 28

When is the 9:3:3:1 ratio used? What is an exception to it

Answer 28

• Parents that are both heterozygous for both genes
• Linked genes

Question 29

What can be deduced from a chi-squared test?

Answer 29

Whether genes are linked or unlinked.
x^2 > p = linked
x^2 < p= unlinked