lecture 19 - extension of mendelian genetics

Question 1

What is Mendel’s First Law?

Answer 1

Law of segregation - Genes segregate at meiosis so that each gamete contains only one of the two posed by the parent.

Question 2

What is Mendel’s second law?

Answer 2

Law of independent assortment - Alleles of different genes assort independently during gamete formation.

Question 3

What is a dihybrid cross?

Answer 3

A cross between two individuals with two observed traits controlled by two seperate genes (e.g. colour AND wrinkling of Mendel’s peas)

Question 4

What does the product rule determine in Mendelian genetics?

Answer 4

The probability of independent events occurring (i.e. the supply of an allele from two parents).

Question 5

For two traits in a dihybrid cross, how can the probability of having two specific different traits be calculated?

Answer 5

Multiply the probability of each different trait.

Question 6

How can the probability of having a specific genotype be calculated?

Answer 6

Chance of getting from mother multiplied by chance of getting from father.

Question 7

What does the sum rule determine in Mendelian genetics?

Answer 7

The probability of 2 mutually exclusive events occurring. (e.g. getting one phenotype OR the other)

Question 8

How is the probability of getting one genotype OR the other calculated?

Answer 8

Sum rule - sum the probability of both occurring.

Question 9

What is polymorphism?

Answer 9

When a single gene has more than 2 possible alleles (rather than just dominant or recessive), but the individual will only inherit two alleles, 1 on each homologous chromosome.

Question 10

What is incomplete dominance?

Answer 10

A form of intermediate inheritance, where one allele for a specific trait is not completely expressed over its paired allele, resulting in a third phenotype that is a combination/blend of the two alleles.

Question 11

In incomplete dominance, can heterozygous individuals with ‘blended’ phenotypes produce offspring with ‘unblended’ phenotypes?

Answer 11

Yes - particulate inheritance means they will pass on either the dominant or recessive allele, rather than an entirely new allele.

Question 12

What is codominance?

Answer 12

When 2 alleles for a specific gene are both expressed, rather than having one dominant and one recessive.

Question 13

What is a common example of codominance in humans?

Answer 13

Blood type - both parental genotypes are expressed in the phenotype.

Question 14

What are polygenic traits?

Answer 14

Phenotype is controlled by many genes that have an additive effect, so characteristics appear continuous or quantitive. e.g. skins colour.

Question 15

What is the distribution of phenotype for polygenic traits?

Answer 15

Normal distribution curve.

Question 16

How does the environment affect phenotype distribution?

Answer 16

Can smooth differences among phenotypes, resulting in a more continuous range of possible outcomes in the population.