1.4. Extension of Mendelian Genetics

Question 1

If a heterozygote produces an intermediate phenotype, and neither the parental allele is dominant nor recessive to the other other, this is known as ____; what is its ratio?

Answer 1

incomplete/partial dominance; 1:2:1

Question 2

if the heterozygote expresses the phenotypes of both homozygotes and neither allele is dominant or recessive, this is known as ___; what is its ratio? ex: MN blood group in chromosome 4

Answer 2

codominance; 1:2:1

Question 3

when there are three or more alleles of the same gene found and can only be studied in a population, this is known as ____; ex: ABO blood groups in chromosome 9

Answer 3

multiples alleles

Question 4

rare recessive mutation of FUT1 coding for fucosyl transferase which results in the incomplete formation of the H substance; hence, blood type O is expressed

Answer 4

bombay phenotype

Question 5

this type of allele affects the organism’s viability and survival; mutations resulting in a non-functional gene product; early expression: embryo death; late expression: die later

Answer 5

lethal allele

Question 6

type of lethal allele wherein just one copy of the allele results in the individual’s death; lethal effects occur in heterozygotes but may be delayed. what is its ratio? ex: huntington’s disease

Answer 6

dominant lethal allele; 2:1

Question 7

type of lethal allele wherein a homozygous recessive is required to be lethal; heterozygotes tolerate the lethal allele but may also result in a distinctive mutant phenotype; what is its ratio? ex: yellow coat in mice

Answer 7

recessive lethal allele; 1:2

Question 8

two cases where dihybrid ratio is modified

Answer 8

(1) combination of two gene pairs with two modes of inheritance
(2) a single phenotype is affected by more than one set of genes

Question 9

expression of one gene pair masks or modifies the effect of another gene pair; the allele that masks is called ___ while the allele being masked is called ___.

Answer 9

epistasis; epistatic allele; hypostatic allele

Question 10

type of epistasis wherein there is complete dominance at both gene pairs, and when one gene is dominant, it masks the effect of the other; what is its ratio?

Answer 10

dominant epistasis; 12:3:1

Question 11

type of epistasis wherein there is complete dominance at both gene pairs, and when one gene is homozygous recessive, it hides or masks the effect of the other.

Answer 11

recessive epistasis; 9:3:4

Question 12

occurs when there is a complete dominance at both gene pairs, and when either gene is dominant, it is epistatic to the other; what is its ratio?

Answer 12

duplicate geness; 15:1

Question 13

gene interaction wherein the presence of at least one dominant allele of each of the two gene pairs is essential to display the genotype; what is its ratio?

Answer 13

complementary gene interaction; 9:7

Question 14

gene interaction wherein there is complete dominance at both gene pairs, and new phenotypes result from either (1) interaction between dominants or (2) interaction between homozygous recessives; what is its ratio?

Answer 14

novel phenotypes; 9:6:1

Question 15

what is pleiotropy?

Answer 15

source of modification wherein there are multiple phenotypic effects of a single gene; ex: phenylketonuria gene causing mental impairment, light hair color, and metabolites in blood and urine

Question 16

what are x-linked genes?

Answer 16

other source of modification; unique pattern of inheritance in comparison with autosomal genes

Question 17

what kind of genes are responsible for the existence of contrasting phenotypes?

Answer 17

autosomal genes

Question 18

the expression of a specific phenotype is absolutely limited to one sex; ex: hen feathering in females and cock feathering in males

Answer 18

sex-limited inheritance

Question 19

the sex of an individual influences the expression of phenotype; the phenotype is not limited to one sex or the other; ex: pattern baldness

Answer 19

sex-influenced inheritance

Question 20

the phenotype is affected by mitochondria or chloroplast ; ex: poky (slow-growing mutant strain; related to mitochondria) in neurospora - female poky x wild male = all poky vs. wid female x poky male = all wild type

Answer 20

organelle heredity

Question 21

variegation in 4’oclock plants are caused by (a) mitochondria or (b) chloroplast?

Answer 21

b. chloroplast

Question 22

an organism’s phenotype is determined by their mother’s nuclear gene products stored in the oocyte; ex: embryonic development in drosophila

Answer 22

maternal effect

Question 23

physical location of a gene in relation to other genetic material may influence phenotypic expression. what is it called? ex: when w+ is moved near a heterochromatin (chromosome that is condensed and genetically inert), it becomes variegated instead of normal

Answer 23

position effect

Question 24

as traits are passed down from one generation to another, they seem to grow and appear stronger, influencing phenotypic expression. what is this called? ex: myotonic dystrophy wherein the size of the repeated dna segment increases, resulting in a much more pronounced trait

Answer 24

genetic anticipation

Question 25

percentage of individuals showing at least some degree of expression of a mutant genotype

Answer 25

penetrance

Question 26

the phenomenon wherein the genotype is present but not observable physically is called ___.

Answer 26

incomplete penetrance

Question 27

range of phenotypic expression of a given genotype

Answer 27

expressivity

Question 28

when a trait is not manifested uniformly among individuals that show it, this is referred to as ____.

Answer 28

variable expressivity