Chapter 3d - Genes of Variable Expressivity

Question 1

Genes of Variable Expressivity

Answer 1

1. Pleiotropy
2. Penetrance
3. Phenocopy

Question 2

single mutation simultaneously affects several traits

Answer 2

pleiotropy

Question 3

examples of pleiotropy

Answer 3

1. sickle cell anemia
2. phenylketonuria (PKU)
3. Marfan syndrome
4. porphyria variegata (vampire’s disease)

Question 4

what does the alleles of the b–globin gene influence

Answer 4

• type of hemoglobin produced
• red blood cell shape
• susceptibility to anemia
• malaria resistance
• organ function
• life-span

Question 5

• rare inherited disorder that causes an amino acid called phenylalanine to build up in the body
• caused by a change in the phenylalanine hydroxylase (PAH) gene. This gene helps create the enzyme needed to break down phenylalanine

Answer 5

phenylketonuria (PKU)

Question 6

caused by defects in gene called fibrillin-1, an important building block for connective tissues in the body

Answer 6

Marfan Syndrome

Question 7

manifestations of Marfan Syndrome

Answer 7

1. Pectus excavatum
2. arachnodactyly
3. dilation of aorta

Question 8

• group of rare, genetic blood disorders that impact the production of hemoglobin, the iron-rich protein that transports oxygen in the blood
• Cutaneous porphyrias (porphyrias affecting the skin) leads to sensitivity to sun and light

Answer 8

porphyria variegata (vampire’s disease)

Question 9

Ex. of people with Marfan Syndrome

Answer 9

1. Abraham Lincoln
2. Osama bin Laden

Question 10

Ex. of people with porphyria variegata

Answer 10

1. King George III
2. Vincent van Gogh
3. Nebuchadnezzar
4. Paula Frias Allende

Question 11

given genotype may or may not show phenotype

Answer 11

penetrance

Question 12

Two types of penetrance

Answer 12

1. complete penetrance
2. incomplete penetrance

Question 13

all individuals express a given genotype

Answer 13

complete penetrance

Question 14

not all would express a given genotype

Answer 14

incomplete penetrance

Question 15

ex. of incomplete penetrance

Answer 15

1. Harelip
2. Dominant retinoblastoma

Question 16

• malignant eye tumor in children
• 90% penetrance

Answer 16

dominant retinoblastoma

Question 17

when penetrant:
degree in which a particular phenotypic effect is exhibited in an individual

Answer 17

expressivity

Question 18

two types of expressivity

Answer 18

1. constant expressivity
2. variable expressivity

Question 19

trait in all individuals is identical

Answer 19

constant expressivity

Question 20

ex. of constant expressivity

Answer 20

1. kinky hair
2. vestigial wings in Drosophila

Question 21

not identical expression of trait

Answer 21

variable expressivity

Question 22

ex. of variable expressivity

Answer 22

1. polydactyly
2. mouse spotting

Question 23

penetrance and expressivity

Answer 23

1. penetrance, with complete expression
2. penetrance, with moderate expression
3. penetrance, with minimal expression
4. no penetrance, thus no expression

Question 24

what influence the degree of penetrance and expressivity

Answer 24

• modifier genes
• environment

Question 25

identical known genotypes yield 100% expected phenotype

Answer 25

complete penetrance

Question 26

identical known genotypes yield <100% expected phenotype

Answer 26

incomplete penetrance

Question 27

identical known genotypes with no expressivity effect yield 100% expected phenotype

Answer 27

constant expressivity

Question 28

identical known genotypes with an expressivity effect yield a range of phenotypes

Answer 28

variable expressivity

Question 29

identical known genotypes produce a broad range of phenotypes due to varying degrees of gene activation and expression

Answer 29

incomplete penetrance with variable expressivity

Question 30

- environmentally-induced phenotype which closely resembles the phenotype by a known recessive gene - or 'aritifical phenotype'

Answer 30

phenocopy

Question 31

ex. of phenocopy

Answer 31

1. insulin-dependent diabetics 2. thalidomide babies 3. phenylketonuria of normal babies with mothers with PKU

Question 32

- used as sleeping pill and tranquilizer in the early 1960s taratogenic when used during the first trimester of pregnancy - mimics a recessive disorder, phocomelia, characterized by abnormalities in the bones of arms and/or legs

Answer 32

thalidomide

Question 33

what does thalidomide babies mimic

Answer 33

phocomelia

Question 34

what helps determine expression of genotype

Answer 34

environmental conditions

Question 35

what changes the color of hydrangea flowers

Answer 35

pH of soil

Question 36

carries allele specifying heat-sensitive enzyme for melanin production

Answer 36

himalayan rabbit

Question 37

some effects of the environment

Answer 37

1. age of onset (male pattern baldness) 2. sex (male pattern baldness) 3. temperature

Question 38

what does temperature influene

Answer 38

- enzymes - coloration in Siamese cats - sex determination in reptiles

Question 39

occurs more often in females than males due to the presence of estrogen

Answer 39

rheumatoid arthritis

Question 40

baldness: BB

Answer 40

bald in either sex

Question 41

baldness: Bb

Answer 41

bald in males only

Question 42

baldness: bb

Answer 42

normal hair in both

Question 43

- traits where an allele is dominant in one sex but recessive in the opposite sex - does not mean sex-linked

Answer 43

sex-influenced traits

Question 44

sex influence is a phenomenon of __

Answer 44

heterozygotes

Question 45

sex-influenced traits are __, meaning it is not sex-linked

Answer 45

autosomal

Question 46

ex. of sex-influenced traits

Answer 46

scurs (hornlike growth) in cattle

Question 47

found in both sexes but manifested only in one sex due to physiological/anatomical reasons

Answer 47

sex-limited traits

Question 48

ex. of sex-limited traits

Answer 48

1. genes for milk production in both bulls and cows 2. genes for long pointed feathers in cocks and hens 3. genes for beard development in men and women