Lecture 14

Question 1

How is Gene linkage an exception to Mendelian Genetics?

Answer 1

Genes on the same chromosomes do not assort independently of each

Question 2

How are Sex linked genes an exception to Mendelian Genetics?

Answer 2

Sex linked genes do not exhibit the same ratios in both sexes

Question 3

How is incomplete dominance an Exception to Mendelian genetics?

Answer 3

In a dihybrid cross it will give a 1:2:1 ratio

Question 4

How is Incomplete penetrance an exception to Mendelian genetics?

Answer 4

Sometimes individuals with a certain genotype do not have the corresponding phenotype

Question 5

What is Variable expressivity?

Answer 5

Differences in the strength of a phenotype within individuals

Question 6

How is Variable Expressivity an exception to Mendelian Genetics?

Answer 6

This changes the expected phenotypes

Question 7

How is Functional Mosaicism an exception to Mendelian Genetics?

Answer 7

When there is random inactivation of an X chromosome the phenotypes may vary

Question 8

What is the shape of DNA in mitochondria?

Answer 8

Circular, with multiple copies throughout the cell

Question 9

What is union rental inheritance?

Answer 9

When organelles in a cell are either inherited from the mother or the father but not both

Question 10

What is Homoplasmy?

Answer 10

When all mtDNA copies are identical

Question 11

What is Heteroplasmy?

Answer 11

When there is a mixture of mutant and normal mtDNA copies in a cell

Question 12

What genes are encoded for in mitochondrial DNA in humans?

Answer 12

Genes for oxidative phosphorylation
Ribosome components
Translation machinery like tRNA

Question 13

What does a pedigree look like for a mitochondrial disease?

Answer 13

The mothers pass it on to all their children and affected fathers never transmit to offspring

Question 14

Why does LHON occur?

Answer 14

Because mitochondria are very important in retinal cells mutation in this will cause the disease

Question 15

What can cause Heteroplasmy?

Answer 15

When mitochondria replicate they divide by binary fission. Since there are multiple copies of mitochondrial DNA within the mitochondria they do not get distributed evenly so some may have multiple copies of the mutant DNA while some get normal copies. Also in gamete formation there isn’t even distribution of mitochondria so some may receive mitochondria with more of the mutated DNA

Question 16

How is embryonic lethality an exception to Mendelian Genetics?

Answer 16

Embryonic Lethality will affect the ratio of genotype. For example a homozygous dominant condition will cause the embryo to die before being born

Question 17

What would be the ratio if we observed Gene redundancy?

Answer 17

15:1 in the “other” phenotypic ratio

Question 18

What cause an organism to still appear wild type even though reverse genetics has removed a gene?

Answer 18

The researcher may not be looking in the correct place/testing the correct condition
The gene may have subtle effects on the fitness and species
It could also be due to gene redundancy where one gene compensates for the loss of function of another

Question 19

What are duplicate genes in gene redundancy known as?

Answer 19

Paralogs

Question 20

What is the ratio in Recessive Epistasis?

Answer 20

9:3:4

Question 21

What is Epistasis?

Answer 21

When an allele of one gene masks/influences the phenotypic effects of the alleles of the other gene

Question 22

What is Recessive Epistasis?

Answer 22

When the phenotype of homozygous recessive alleles conceals the phenotype of either allele from a different gene

Question 23

What is Dominant Epistasis?

Answer 23

When the phenotype of a dominant allele conceals the phenotype of wither allele from a different gene

Question 24

What is the Ratio in Dominant Epistasis

Answer 24

12:3:1

Question 25

What is the ratio in complementation?

Answer 25

9:7

Question 26

What are Conditional Mutations?

Answer 26

Mutations that have a Wilde type or less severe phenotype under certain (permissive) environmental conditions

Question 27

When is the mutant phenotype seen in conditional mutations?

Answer 27

At non-standard temperature is the mutant phenotype is expressed. This temperature is called the restrictive temperature

Question 28

What causes Conditional mutations?

Answer 28

Usual missense mutations