Chapter 3c - Lethal Genes

Question 1

• needed for survival
• makes up approx. 1/3 of all genes
• exists in the dominant and recessive condition

Answer 1

essential gene

Question 2

essential gene makes up __ of all genes

Answer 2

1/3

Question 3

• mutation in an essential allele that results in death
• lethality due to absent or malfunctioning protein
• mostly recessive but can be dominant

Answer 3

lethal allel

Question 4

• cause lethality when homozygous recessive
• produce recognizable phenotype in heterozygote

Answer 4

recessive lethal gene

Question 5

when was lethality first reported

Answer 5

1905 by Cuenot while working on mice (body color)

Question 6

M^L interferes with normal spine development

Answer 6

Manx cat

Question 7

• happens because of a mutation (change) in a gene called COMP
• change causes a problem with how bone and cartilage grow
• bones end up shorter than they typically would be.

Answer 7

Pseudoachondroplasia

Question 8

• heterozygotes show heavy freckling
• homozygous recessive - with fatal skin cancer due to extreme sensitivity to UV, stunted growth, epilepsy

Answer 8

Xeroderma pigmentosum

Question 9

situation where recessive lethal alleles are present on two homologous chromosomes

Answer 9

balanced lethal system

Question 10

only expressed alleles are subject to __ __

Answer 10

natural selection

Question 11

in diploid organisms, recessive alleles can be protected from being __ in __

Answer 11

eliminated in heterozygotes

Question 12

sickle-cell disease is an example of what

Answer 12

balanced polymorphism

Question 13

if dominant and immediate in expression, all individuals with genes will die and gene will be lost

Answer 13

dominant lethal genes

Question 14

heterozygote has tumor-like formation in various organs and skin, severe mental defects leading to early death

Answer 14

epiloia

Question 15

• disease attacks areas of the brain that help to control voluntary (intentional) movement, as well as other areas
• People living with this develop uncontrollable dance-like movements (chorea) and abnormal body postures, as well as problems with behavior, emotion, thinking, and personality

Answer 15

Huntington’s chorea

Question 16

what are enlarged in people with Huntington’s disease

Answer 16

frontal horns of the lateral ventricles

Question 17

allele in chickens which causes its legs to be short and stunted

Answer 17

creeper allele

Question 18

what is the creeper allele

Answer 18

dominant