Chapter 2 - Single Gene Inheritance

Question 1

gene discovery

Answer 1

the process whereby a biological property (trait) is investigated by finding the subset of genes in the genome that influence this property

Question 2

wild type

Answer 2

the most common form of any property of an organism

Question 3

mutants

Answer 3

the heritable variants observed in an organism that differs from the wild type

Question 4

phenotypes

Answer 4

the alternative forms of the property

Question 5

polymorphisms

Answer 5

the coexistence of two or more reasonably common phenotypes of a biological property

Question 6

What are the general steps of functional analysis by gene discovery?

Answer 6

1) amass mutants affecting biological property of interest
2) cross mutants to wild type, observe ratios, is there single-gene inheritance?
3) deduce function of gene at molecular level
4) how do genes interact with other genes to produce the property in question?

Question 7

genetic dissection

Answer 7

the use of mutants to identify/separate a gene affecting a specific property

Question 8

forward genetics

Answer 8

a type of approach to gene discovery that starts with random single-gene mutants and ends with their DNA sequence and biochemical function

Question 9

mitosis

Answer 9

forms two identical copes of itself (sister chromatids)

Question 10

meiocytes

Answer 10

specialized diploid cells that divide to produce sex cells/gametes

Question 11

meiosis

Answer 11

consists of two nuclear divisions, producing four cells from the progenitor cell

Question 12

dyad

Answer 12

replicate sister chromosomes that are together

Question 13

bivalent

Answer 13

the unit comprising the pair of synapsed dyads

Question 14

tetrad

Answer 14

the four chromatids that make up a bivalent (four homologs)

Question 15

ascus

Answer 15

a membranous sac containing products of a tetrad (four spores) - associate with fungi, algae, haploid meiosis

Question 16

null alleles

Answer 16

proteins encoded by these alleles completely lose their function

Question 17

null mutation

Answer 17

a mutation that results in a complete lack of function

Question 18

leaky mutations

Answer 18

result of mutant alleles that reduce the level of protein function although some “wild type” functions may still exist

Question 19

silent mutations

Answer 19

mutations that have no effect, appear to be functionally wild type

Question 20

most mutations that alter phenotype also alters:

Answer 20

the amino acid sequence of the gene’s protein product, which can lead to reduced or absent functions

Question 21

haplosufficient

Answer 21

one gene copy has enough function to produce a wild-type phenotype (ex dominant genes)

Question 22

null mutations in haplosufficient genes result in:

Answer 22

recessiveness, no change in phenotype

Question 23

haploinsufficient

Answer 23

the single wild-type allele cannot provide enough product for normal function

Question 24

null mutations in haploinsufficient genes would result in:

Answer 24

a change in phenotype because the null mutant allele would be “dominant”

Question 25

test cross

Answer 25

the cross of an unknown genotype with a fully recessive individual

Question 26

tester

Answer 26

fully recessive individual

Question 27

sex chromosomes determines:

Answer 27

sex of the individual

Question 28

homogametic sex

Answer 28

females, gametes are of only one type

Question 29

heterogametic sex

Answer 29

males

Question 30

dioecious species (plants)

Answer 30

show animal-like sexual dimorphisms

Question 31

X and Y chromosomes can be divided into:

Answer 31

homologous (counterpart present on other chromosome) and differential (no counterpart on other chromosome) regions

Question 32

in males, genes in the differential regions are HEMIZYGOUS

Answer 32

do not have counterparts on X chromosome

Question 33

sex linkage

Answer 33

genes in the differential region on sex chromosomes that demonstrate inheritance patterns

Question 34

X-linkage

Answer 34

mutant alleles in the differential region of X chromosomes

Question 35

Y-linkage

Answer 35

mutant alleles in the differential region of Y chromosomes

Question 36

pseudoautosomal regions 1 and 2

Answer 36

a homologous region at each end of the X and Y chromosomes that allow these regions to pair up and cross over in meiosis

Question 37

sex-linked inheritance shows different phenotypic ratios in:

Answer 37

the two sexes of the progeny as well as in reciprocal crosses

Question 38

propositus

Answer 38

the member of the family that first comes to a geneticist’s attention

Question 39

autosomal recessive disorders

Answer 39

disorder appears in progeny (sons and daughters) of unaffected parents, it is the result of a single recessive mutant gene

Question 40

autosomal dominant disorders

Answer 40

defective allele is dominant, disease appears in every generation

Question 41

autosomal polymorphisms

Answer 41

contrasting morphs are often inherited as alleles of a single gene

Question 42

X-linked recessive disorders

Answer 42

more males display the mutant phenotype

Question 43

X-linked dominant disorders

Answer 43

affected males pass condition on to daughter but not son

Question 44

Y-linked inheritance

Answer 44

only males inherit these genes, ex SRY gene that determines “maleness”