ch 15

Question 1

chromosomal theory of inheritance

Answer 1

mendelian genes have specific loci (positions) along chromosomes and it is the chromosomes that undergo segregation and independent assortment

Question 2

sex linked gene

Answer 2

a single gene located on either sex chromosome

ex. X-linked genes
3 options for females
only 2 options for males

Females
–  XNXN  normal 
–  XNXn  normal 
–  XnXn   colorblind
Males 
 –  XNY   normal 
–  XnY     colorblind 

certain notation: X^allele

Question 3

homologous pair #23

Answer 3

sex chromosomes are not truly homologous

Y is much smaller than X and carries less genes

XX= female
XY = male

Question 4

linked genes

Answer 4

two or more genes on the SAME chromosome that tend to be inherited together

genes located near each other on the same chromosome tend to be inherited together in genetic crosses

unlinked = not on same chromosome

Question 5

X inactivation in females

Answer 5

almost all of one X chromosome in each cell in female mammals becomes inactivated during early embryonic development

Question 6

wild type

Answer 6

displays normal phenotype

Question 7

mutant phenotype

Answer 7

mutations in the wild type allele; displays unusual phenotype

Question 8

recombination frequency formula

Answer 8

recombinants / # total offspring x 100%

Question 9

nondisjunction

Answer 9

the members of a pair of homologous chromosomes do not move apart properly during meiosis I or sister chromatids fail to separate during meiosis II

one gamete receives two of the same type of chromosome and the other gamete receives no copy

Question 10

aneuploidy

Answer 10

this results from nondisjunction; if either of the irregular gametes unites with a normal one at fertilization, the zygote will also have an abnormal number of a particular chromosome

Question 11

Heterozygotes can be ______

Answer 11

carriers

Question 12

Females are _____ of two types of cells;

which are what ?

Answer 12

mosaics, which is the presence of two or more populations of cells with different genotypes in one individual, who has developed from a single fertilized egg

Question 13

What was model genetic system?

Answer 13

Drosophilia; form of a test cross

crossing over occurred because results weren’t 1:1:1:1
the rare flies were due to crossing over!

wildtype = normal

Question 14

recombinant offspring

Answer 14

these are rare because they are from crossing over; this will be the smaller number or outcome amount

Question 15

parental type offspring

Answer 15

these are more common and match the parents

Question 16

What is the likely hood of crossing over occurring on a chromosome?

Answer 16

• The closer together genes are on a chromosome, the less likely there will be a crossover because there is less space
• Genes farther apart will have a greater chance of crossing over- more options because more space

Question 17

genetic map

Answer 17

o 1% = one map unit

o Maximum distance is 50%

Question 18

translocation

Answer 18

moves a segment from one chromosome to a non homologous chromosome

Question 19

Barr body

Answer 19

the inactive X in each cell of a female condenses into a compact object called a Barr body, which lies along inside of nuclear envelope

Question 20

law of independent assortment

Answer 20

alleles of genes on non homologous chromosomes assort independently

occurs during metaphase I and then they separate during anaphase I

Question 21

law of segregation

Answer 21

two alleles for each gene separate during gamete formation

Question 22

X-linked genes

Answer 22

the human x chromosome contains 1,100 genes

ex. hemophilia

Question 23

genetic recombination

Answer 23

production of offspring with combinations of traits that differ from those found in either P generation parent

Question 24

crossing over

Answer 24

accounts for recombination of linked genes

Question 25

linkage map

Answer 25

a genetic map based on recombination frequencies

Question 26

map units

Answer 26

one map unit = 1% recombination frequency

Question 27

genetic map

Answer 27

an ordered list of the genetic loci along a chromosome

max is 50%

Question 28

deletion

Answer 28

occurs when a chromosomal fragment is lost

Question 29

duplication

Answer 29

the “deleted” fragment may become attached as an extra segment to a sister chromatid

Question 30

inversion

Answer 30

a chromosomal fragment may also reattach to the original chromosome but in the reverse orientation

Question 31

What is the probability that a human male will inherit an X-linked recessive allele from his father?

Answer 31

0% because a son cannot receive an X chromosome from his father.

Question 32

A woman is a carrier for red-green color blindness, a sex-linked trait. Her husband is normal (not color-blind) for this trait. What are the chances that their newborn daughter will be red-green color-blind?

Answer 32

0% The father only has a single, normal allele.

Question 33

Consider a woman who is a carrier of a recessive X-linked allele for hemophilia. Which of the following possibilities could explain the presence of the hemophilia allele in her genotype?

Answer 33

Either her mother was a carrier or her father had hemophilia.

Question 34

what mechanism can break a linkage?

Answer 34

crossing over

Question 35

Morgan’s experiments using Drosophila examined the inheritance patterns of the white eyed phenotype. The results provided evidence that:

Answer 35

the gene for white eye is on the X chromosome

Question 36

____________ is a mechanism that breaks linkage between genes.

Answer 36

crossing over