Inheritance and Pedigree Analysis

Question 1

Mendel’s Law of Segregation

Answer 1

alleles segregate from ea other during formation of gametes; half of the gametes carry one allele and other half of the gametes carry the other allele; then at fertilization gametes from ea parent are randomly combined

Question 2

Monohybrid Cross

Answer 2

YY x yy

Genotype ratio is 1:2:1
Phenotype ratio is 3:1

Question 3

Mendel’s Law of Independent Assortment

Answer 3

genes for diff traits assort indep of one another in formation of gametes; these rules apply only if ea trait located on DIFFERENT chromosome and if the traits are independent (if the two traits are are on same chromosome they will be inherited together)

Question 4

Dihybrid Cross

Answer 4

YYRR x yyrr

• Gametes would be YR or yr —> YyRr (F1 generation)
• Then cross F1 generation… YyRr x YyRr (Phenotype ratio: 9 dom dom: 3 dom rec: 3 rec dom: 1 rec rec)

Question 5

Proband

Answer 5

Person that first brings attention to Dr or geneticist (rep by arrow on pedigree)

Question 6

Pedigree terms/rules/symbols

Answer 6

Male- square 
Female- circle 
Arrow pointing to proband
Vert lines b/n generation and horizontal lines b/n sibs 
Affected ppl are filled
Deceased crossed out

Question 7

Recurrence Risk

Answer 7

Likelihood that a trait or disorder present in one family member will occur again in other family members in the same or subsequent generation

Question 8

Autosomal Dominant Inheritance

Answer 8

• Vertical pattern of inheritance (affected people in ea generation)
• Affected individuals always have affected parent
• Recurrence risk is 50% so half kids born to one affected parent will be affected
• Unaffected people have normal children (b/c both yy)
• Both males and females can be affected and spread to kids

Question 9

How does the dominant gene affect proteins in autosomal dominant disorders? (3)

Answer 9

1- haploinsufficiency (not enough of the wild type allele produced for normal protein function)
2- gain-of-function (gene product of mutated allele causes new abnormal function)
3- dominant-negative effect (mutated allele works to inhibit the wild type allele)

Question 10

Autosome Recessive Disorders

Answer 10

Both alleles must be altered

• Trait may be found in siblings
• Parents usually healthy but carry one altered allele
• Horizontal pattern of inheritance
• Recurrence risk is 1/4 (parents have 25% chance of having 2nd affected child if both parents are heterozygous)
• Trait may appear as isolated sporadic event
• Parents of affected children may be related (consanguineous marriages) inbred
• Males and females equally affected

Question 11

Consanguinity
Inbreeding
Incest

Answer 11

• Consanguinity= 1+ ancestors in common up to great grandparent/ second cousin
• Inbred= offspring of marriage b/n consanguineous individuals
• Incest= Consanguineous marriage forbidden by law

Question 12

X-Linked Recessive Inheritance

Answer 12

Disease gene lies on X chromosome (need 2 affected alleles for disase)

• No male-to-male transmission; men only give Y to son and so all daughters of affected males will be carriers
• Disease can skip generation
• Affected males have phenotypically normal offspring but daughters are always carriers (b/c give sons Y and daughters just carry affected X)
• Affected males are related through mothers (carriers)
• Female carriers will pass abnormal gene to 1/2 offspring (those male offspring will then automatically have it and those daughters will be carriers)
• Female carriers may have mild symptoms due to unequal activation of X chromosomes
• Unaffected males do not transmit disorder (not carriers)

Question 13

X-Linked Dominant Inheritance

Answer 13

Disease lies on X-chromosome (only need one affected allele to have disease)

• Both males and females affected
• Fathers pass gene to ALL daughters but NO sons
• Pattern of inheritance from mother is same as autosomal dominant
• Frequently lethal in males

Question 14

Mitochondrial Inheritance

Answer 14

mtDNA- mito genome - only 37 genes

• Most involved in oxidative phosphorylation
• Maternal inheritance
  
  • B/c only ova cells contribute mito to embryo
  • Pedigree shows only moms pass it on
• Rules of transmission-
  
  • 1- affected mothers pass disease to ALL children
  • 2- affected males do NOT pass to any children
  • 3- both sexes equally affected

Question 15

Semi-Dominance v. Co-dominance

Answer 15

Semi= intermediate phenotype (pink roses)
Co-Dom= ea allele produces phenotype indep of ea other (ABO blood type)

Question 16

Linkage

Answer 16

-if 2 genes are close together on single chromosome, they are likely to be inherited together (closer they are the greater the chance of being inherited together)

Question 17

Variable Expressivity v. Variable Penetrance

Answer 17

Expressivity= 2 people w/ same disease genotype may have varying severity in phenotype

Penetrance= not all people w/ disease genotype have the disease (other factors may be involved) penetrance is given as a percentage for a specific disease

Question 18

Anticipation

Answer 18

Earlier age of onset and inc severity w/ ea new generation

Question 19

Mosaicism

Answer 19

When embryo undergoes mutation during development (so mutation is not inherited) —> mosaic phenotype (some cells have bad gene and others have good gene)
**Dep on what stage of development (early in development —> more cells affected)

Germline (alters sperm or egg) v. somatic (alters non-germ cells)

Question 20

Epistasis

Answer 20

Interaction of 2+ genes to produce a phenotype