lethal genes

Question 1

lethality

Answer 1

-if an allele makes one of these genes non-functional, or causes it to take on an abnormal harmful activity, it may be impossible to get an organism with that geneotype (usually heterozygous)

Question 2

lethal genes

Answer 2

-genes which result in the reduction of viability of an individual or become a cause of death
-usually a result og mutations in genes that are essential for growth or development
-can cause death prenatally or any time after birth

Question 2

history behind lethal genes and when

Answer 2

-lucien cuenot in 1905 discovered lethal alleles

Question 3

how were lethal alleles discovered (outline the experiment)

Answer 3

-wild type alele (A) produced a blend of yellow and black pigmentation in each hair of the mouse (agouti colour). one mutant allele AYis a much lighter yellowish colour. when two yellow mice were crossed (AyAy=lethal) so 2/3 yellow and AA-1/3 agouti cuz only 3 survivors. so we get 2:1 instead of the expected 3:1 yellow to agouti
-first documented example of lethal genes

Question 4

recessive lethals

Answer 4

-most common type of lethal genes
-lethal only at homozygous conditions
eg) sickle cell, cystic fibrosis

Question 5

eg. manx cats

Answer 5

-breed w no tails
-caused by genetic mutation from likley high rate of inbreeding.
-mutated gene shortens their tails to varying degrees:
1. rumpy (no tail at all)
2. rumpy riser (small stub)
3. stumpy
4. longy
5. fully tailed
-taillessness is due to locus M and MM results in lethality early in development
-homozygous dom results in death

Question 6

eg. creeper chickens

Answer 6

-creeper chickens are characterised by v sort wings and legs
Cp=allele for creeper trait
cp=allele for normaltrait
therefore; Cpcp=creepers and cpcp=normal CpCp=death in early development

Question 7

eg. sickle cell anemia

Answer 7

-rbc are disk-shaped and easily flow thru blood vessels. sickle are crescent moon shaped and stick together, blocking vesels easily.
-alleles are HbA and HbS-> 2 diff forms of hemoglobin (differ by a single amino acid)
HbSHbS=shows symptoms of sickle cell (all bad rbc, fatal post birth)
HbAHbA=healthy (no sign of sickle cell at all, all normal rbc, but suceptible to malaria)
HbAHbS=healthy (but some cells have sickle cell formation)

Question 8

eg. cystic fibrosis

Answer 8

• progressive lethal recessive genetic disorder that causes persistent lung infections and limits ability to breathe over time
  -caused by a number of mutaions in a single cystic fibrosis transmembrane conductance regulator (CFTR) gene
  -C=allele for normal
  -c=allele for cystic fibrosis
  heterozygous is carrier and unaffected

Question 9

why are dominant lethals not commonly found

Answer 9

-cuz its fatal if dom homo and hetero. These alleles are not commonly found in populations because they usually
result in the death of an organism before it can transmit its lethal allele on
to its offspring
– This allele can only be transmitted if the lethality phenotype occurs after
reproductive age

Question 10

eg. huntington’s disease

Answer 10

-lethal dominant
-rare neurodegenerative disorder that ultimately results in death.
-in heterozygotesthe disease is delayed, usually well into adulthood. they will inevitably develop the fatal disease
- the onset of disease may not occur until like 40 at which point they may have passed allele to 50% of their offspring

Question 11

conditional lethals

Answer 11

-these alleles turn deadly only when there is an external enviornmental aspect involved

Question 12

eg. favism

Answer 12

-eg of conditional lethal