1-19 Mendelian Inheritance Pedigree Analysis

Question 1

Holandric genes

Answer 1

on Y chromosome

Question 2

Sex limited traits

Answer 2

only manifest in one sex, not necessarily on the x or y

Question 3

Penetrance

Answer 3

proportion of people with allele (genotype) who manifest the trait (phenotype)

Question 4

expressivity

Answer 4

severity of trait, many traits are not just present or absent but expressed at varying degrees

Question 5

Locus

Allele

Answer 5

site on chrom where a gene is located

alternative forms of a gene at a particular locus, most genes there are 2 one on each chrom

Question 6

Mendel’s first law

Second law

Answer 6

1. independent segregation

2. independent assortment

Question 7

Autosomal recessive traits / pedigrees

Answer 7

“Horizontal” transmission
males and females equally affected
risk of recurrence in a sibling is 25%
family history is usually negative

heterozygotes are not clinically effected
most result from enzyme deficiency
carriers can be IDed because the level of gene product is approx half normal (gene dosage, but this is fine)

Question 8

autosomal dominant traits / pedigrees

Answer 8

trait expressed when only one allele is present
“vertical transmission”
males and females equally affected
when parent is affect, risk of recurrence in siblings is 50%
if neither parent affected, appearance of trait may result from new mutation

Question 9

co-dominant traits

Answer 9

traits determined by both alleles are expressed, ex. ABO blood groups

at biochemical and molecular level, most alleles are co-dominant

Question 10

X-linked recessive traits

Answer 10

usually expressed only in males
both parents normal
mother carrier: 50% of daughters and sons affected
father carrier: all daughters carriers, no sons affected

Question 11

X-linked dominant traits

Answer 11

expressed in males and females
trasmitted mothers to sons and daughters
from fathers only to daughters

Question 12

gene dosage

Answer 12

if one allele is defective approx half the normal amount of gene product is made
for most enzymes this is enough
most “metabolic” disorders are recessively inherited (autosomaryl recessive homozygous)

hemizigousity (defect in one allele) of X in males may produce disease but mosaisism could change this in efmales

Question 13

lethal x-linked disorders

Answer 13

new mutations account for 33% of all cases
makes gene freq stable since males can reproduce their unfit X, cannot ID if mother is a carrier in a family or if a de novo mut child

Question 14

Neurofibromatosis, familial cafe-au-lait spots

Answer 14

common genetic disorder from dominant mutations in NF1
NF: develop multiple benign tumors/hyperpigmented spots
Familial cafe: only develop spots no tumors,

Question 15

Congenital adrenal hyperplasia

Answer 15

gene linked to human histocompatibility locus (HLA), needed to make cortisol