ch 13: modern understandings of inheritance

Question 1

x-linked / sex-linked genes

Answer 1

the genes resides on the X chromosome

Question 2

males only have 1 X chromosome, so if a disease is coded on that chromosome…

Answer 2

100% of male offspring will have the disease

Question 3

females have 2 X chromosomes, so if a disease is coded on that chromosome…

Answer 3

the offspring could be dominant for the disease, or be a carrier

Question 4

barr body

Answer 4

early in development, in each female cell, one X chromosome is inactivated and is highly condensed, meaning that the genes on this homologue are not expressed

Question 5

because of the barr body, female heterozygous for genes on the X chromosome are…

Answer 5

genetic mosaics

Question 6

genetic mosaics

Answer 6

1) some cells in body inactivate one X chromosome, other cells inactivate the other (random)
2) if female is heterozygous, some cells will express one allele of a trait, others will express the other

Question 7

how come female “carriers” are still not as susceptible as males to sex-linked diseases

Answer 7

because the inactivation is random, so in most cases each organ/tissue has some cells expressing the “good” copy

Question 8

when a zygote is formed, egg and sperm…

Answer 8

equally contribute nuclear DNA but do not equally contribute organelles

Question 9

mitochondrial genes are inherited from the

Answer 9

female parent (maternal inheritance)

Question 10

genetic recombination

Answer 10

crossing over during meiosis 1

Question 11

recombinant gametes

Answer 11

if crossing over occurs, parental alleles are recombined

Question 12

genes that are farther apart on a chromosome have a —– chance of crossing over

Answer 12

greater

Question 13

larger % recombinants =

Answer 13

farther genes are apart

Question 14

if homologues undergo two crossovers between loci, then the parental combination is

Answer 14

restored; leads to an underestimation of the true genetic distance

Question 15

relationship between true distance on a chromosome and the recombination frequency is

Answer 15

not linear

Question 16

odd number of crossovers produce

Answer 16

recombinant gametes (offspring)

Question 17

even number of crossovers produce

Answer 17

parental gametes (parents)

Question 18

how can you tell if two genes are on the same chromosome (inherited together)

Answer 18

the genes would be inherited more than 50% of the time together

Question 19

in three point crosses, loci with the lowest frequency of recombination must be

Answer 19

in the middle because it would need two crossovers

Question 20

if there is no linkage between three genes being crossed, which results would you get

Answer 20

(1/2) * (1/2) * (1/2) = (1/8)

Question 21

if there is a linkage between the genes being crossed, which results would you get

Answer 21

no set ratio; values will not follow a pattern

Question 22

single-nucleotide polymorphisms (SNPs)

Answer 22

affect a single base (letter) of a gene locus

Question 23

nondisjunction

Answer 23

failure of homologues or sister chromatids to separate properly during meiosis

Question 24

aneuploidy

Answer 24

gain or loss of a chromosome
monosomy-loss
trisomy-gain

Question 25

what syndrome is caused by XXY

Answer 25

klinefelter syndrome (can live)

Question 26

what happens to an XXX female

Answer 26

usually nothing; still functional (can live)

Question 27

XO females

Answer 27

turner syndrome; sterile female (can live)

Question 28

OY males

Answer 28

nonviable zygotes (cannot survive)

Question 29

XYY males

Answer 29

jacob syndrome (can live)

Question 30

genomic imprinting

Answer 30

phenotype exhibited by a particular allele depends on which parent contributed the allele to the offspring

Question 31

what happens if DNA is methylated (methylation, imprinted)

Answer 31

the DNA will be inactivated and not be able to transcribe

Question 32

if you only have a chromosome with an imprinted gene, what happens

Answer 32

you get that disease/syndrome

Question 33

pedigree analysis

Answer 33

used to determine the probability of genetic disorders in the offspring

Question 34

amniocentesis

Answer 34

collects fetal cells from the amniotic fluid for examination (needle goes through stomach)