Chapter 17

Question 1

What is genotype and phenotype?

Answer 1

Genotype refers to the genetic makeup of an individual(alleles that makeup the individual, phenotype refers to the observable characteristics of an individual)

Question 2

What are genes and alleles?

Answer 2

A gene is a short section of DNA that codes for a polypeptide
An allele is a different version of the same gene

Question 3

What do dominant and recessive alleles mean?

Answer 3

Dominant allele means that only one allele is needed for a phenotype to be expressed
Recessive allele means that two alleles are needed for the phenotype to be expressed

Question 4

Monohybrid cross

Answer 4

Question 5

Why in genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios.

Answer 5

Random fusion of gametes
Small sample size
Epistasis
Lethal genotypes
Crossing over
Linked genes

Question 6

What is dihybrid inheritance?

Answer 6

The inheritance of two characteristics which are controlled by different genes located on different chromosomes

Question 7

Dihybrid inheritance cross

Answer 7

Question 8

What is the typical phenotypical cross for a dihybrid cross?

Answer 8

9:3:3:1 where the 1 is always the homozygous recessive

Question 9

What is codominance?

Answer 9

when both alleles contribute to and are expressed in the phenotype

Question 10

What are multiple alleles?

Answer 10

a gene with more than two alleles

Question 11

What is the nomenclature of codominant crosses?

Answer 11

Choose a letter (Upper case) describing
the characteristic encoded by the gene
(ie flower colour= C)
each allele will have a “individual” letter
(ie white=W red=R)
The allele will be shown as superscript
(= CW or CR)
If alleles have the same impact on
phenotype the alleles will ALL be in
upper case.

Question 12

What is sex linkage?

Answer 12

genes that are located on either the X or Y chromosome

Question 13

What is autosomal linkage?

Answer 13

when 2 or more genes are carried on the same chromosome

Question 14

What is epistasis?

Answer 14

When the allele of one gene masks the expression of another in the phenotype

Question 15

When will the ratio of a dihybrid cross of two heterozygous parents not be 9:3:3:1?

Answer 15

If there is autosomal linkage(when two genes are on the same chromosome and the ratio will be 3:1
If there is crossing over(in meiosis)

Question 16

If you have autosomal linkage, how are you able to obtain 4 phenotypes when you expected two?

Answer 16

Crossing over introduces new combinations of gametes
In application question:
Largest two phenotypes are due to no crossing over and are on the same chromosome so are more common
3rd largest is also not from crossing over but because they are from recessive alleles so less common
Smallest is due to crossing over which is rare so will result in few gametes being made and thus the least amount of phenotypes