QUESTIONS & ANSWERS FOR CH. 6/7 TEST – GOOD LUCK ON THE TEST
1. Haploid (n) refers to a cell (sex cell) that has half the number of chromosomes that a diploid cell (body cell 2n)
would have. So in the sex cells we are only giving one complete set of chromosomes to the offspring. So the
egg cell is haploid (1 complete set of chromosomes) which combines with a sperm (1 complete set of
chromosomes) in fertilization to bring the chromosome number back to 2n or diploid. Haploid cells would never
be used in a karyotype you would only be doing a karyotype with diploid cells.
2.
Karyotype are pictures of a cell’s chromosomes like you
see to the right. How we arrange them if 1 – size; 2 –
banding caused by staining of the chromosomes; 3 –
location of centromeres. Karyotypes show: Sex of
individual, # of chromosomes, autosomal chromosomes,
sex chromosomes, disorders, homologous chromosomes.
Missing or extra chromosomes are the result of
nondisjunction during meiosis.
#1-22 pairs of chromosomes are autosomal
chromosomes. The word autosomal chromosome tells us
that if the trait or disorder involves one of these
chromosomes, you will set up a regular
dominant/recessive Punnett square. If the trait or
disorder is on the 23rd pair (sex chromosome) you need to set up a sex-linked Punnett square.
Using the karyotype to the right, if I asked how many chromosomes are in this picture, your answer
would be 47.
If I asked how many autosomal chromosomes there are, your answer would be 44 (1-22 x the 2
chromosomes above that #).
If I asked what is the sex of the individual, your answer would be male because there is a “Y”
chromosome (pair #23).
If I asked what disorder, you would answer Klinefelter’s syndrome.
If I asked how many sex chromosomes there are, you would answer 3 (2 X’s & 1 Y)
3. Disorders that could possibly be on the test are Down’s Syndrome, which shows 3 chromosomes are #21
autosomal chromosome. Klinefelter’s is shown in #2 above. Turner’s syndrome would be just like the karyotype
above only for the sex chromosomes there would only be 1 X & nothing else.
4. Mendel’s laws: law of dominant versus recessive. Punnett squares are set up with the first letter of the
dominant trait & it will be capital. Recessive is the same letter only lower case. Law of segregation says that the
chromosome that you got from mom with separate from the chromosome that you got from dad & end up in
different cells. Law of independent assortment says how the chromosomes line up down the equator is
completely random. This allows for different combinations of having so many of mom’s chromosomes versus
dad’s chromosomes go into what cells.
5. Mendel’s generations – to begin Mendel began with Parental generation & they will go on the outside of the
Punnett square. All of their offspring will be in the box of in other words the F1 generation. When Mendel took
2 offspring from the inside of the Punnett square (F1 generation) & did the next cross, everything now in the box
is referred to as the F2 generation.
6. Genotype – write the alleles that are on the inside of a Punnett square.
7. Phenotype – You need to be able to read the alleles & say what the expression of those alleles are shown.
8. Carrier – is someone who is heterozygous for a recessive trait/disorder. You do not have the trait/disorder but
you have one allele for it that you can pass down to your offspring. You cannot be a carrier for a dominant trait
because if you have one allele you will express that trait.
9. SEX-LINKED PUNNET SQUARES: Always set up you Punnett square with the sex chromosomes first. XY for the
man on the top & XX on the side for the girl. REMEMBER NEVER, EVER, EVER PUT AN ALLELE ON THE Y. Then
read the story. If the trait is dominant & if it says the man has the disorder – put a capital letter on his X. If it
says he doesn’t have it – put a lower case letter on his X. If it says the woman is homozygous dominant – she
gets a capital letter on each X. If it says she is heterozygous – she gets a capital letter on one X & a lower case
letter on the other X. If it says she is homozygous recessive – she gets 2 lower case letters. REMEMBER YOU
CANNOT BE A CARRIER ON A DOMINANT DISORDER OR TRAIT. Now for the RECESSIVE disorder or trait. If the
man does not have the disorder or trait he gets a capital letter on the X. If the man does have the disorder he
gets a lower case letter. If it says the woman is homozygous dominant – she gets 2 capital letters. If it says the
woman is a carrier or heterozygous - she gets a capital letter or a lower case letter. If it says she is homozygous
recessive – she gets 2 lower case letters. To read be sure to look either at just the boy or girl Punnett squares &
each box is 50%. If it asking for a child then you will need to read all 4 boxes & each box is 25%. Below 50% of
the boys will have normal vision and 50% will be colorblind. Girls 0% will be colorblind. A child 25% will be
colorblind.
Y
N
X
N
N
N
N
X X
X
n
N
X Y
n
n
X X
X
XY
10. Hybrid is an organism that have alleles that are heterozygous.
11. Nondisjunction is where the chromosomes do not separate during Meiosis (anaphase II) which causes the 2
chromosomes to go into the same cell. Now when fertilization happens there will end up being 3 chromosomes
instead of 2. You can see where it belongs when you assemble the chromosomes into a karyotype.
12. Incomplete dominance you will be told one color or trait is not completely dominant over another or you will
see 3 completely different phenotypes. Ex: black, white & gray flowers - if you were asked to cross a
heterozygous gray flower with a heterozygous gray flower, here is the set up for that incomplete question. C is
used just to represent we are looking at color. Then put a capital letter of the color you are looking at. In this
example gray is heterozygous so you will be using the B for black & W for white. Remember if you mix black
paint with white paint you get gray paint. If this Punnett square asked to cross a black flower you would just use
B’s on the letter C for the one parent. The phenotype for this Punnett square is 1 black flower, 2 gray flowers &
1 white flower.
B
W
C
B
C
W
C
C
B
B
B
CC
CC
B
W
CC
W
W
C C
W
13. Codominance there is no dominant/recessive but you will see you different colors: black color, and white color
for the homozygous colors. In the heterozygous you will have black & white together in the organisms. You will
set it up just like you would in the Punnett square for #8. We have black, white & black & white flowers. If I
asked you to cross a black & white flower with a black & white flower you would set it up exactly like the
Punnett square in #8. However, you phenotype reads: 1 black: 2 black & white: 1 white flower. Remember CO
means together.
14. Set up for dihybrids. Freckles & taste dominant & clear skin & no taste are recessive. Cross a man who is
heterozygous for freckles & homozygous dominant for taste. First set him up with the correct alleles MAN = Ff
TT with a woman who is homozygous dominant for freckles & heterozygous for taste WOMAN = FF Tt Now you
have to look at Mendel’s law of independent assortment. For the man the big F could end up in the cell with the
big T, or the F could end up with the other big T, or the little f could end up with the big T, of the little f could
end up the other big T
FT
FT
fT
fT
FT
Ft
FFTT
FFTT
FfTT
FfTT
FFTt
FFTt
FfTt
FfTt
FFTT
FFTT
FfTT
FfTT
FFTt
FFTt
FfTt
FfTt
FT
Ft
15. Parental generation will be the parents that we start with at the beginning before we do the cross. Those
parents create the F1, which will be inside the box. To create an F2 generation you need to take 2 of the F1
generation put them on the outside of a Punnett square as the parents. Their offspring would be called the F2
generation.
16. Examples of polygenic traits are: height, skin color, hair color, eye color.
17. Blood types that are heterozygous will be written: IA i, IB i Homozygous blood is written: IA IA, , IB IB Remember
A is dominant to O, B is dominant to O that’s why they have the capital letter I with the capital letters. Because
O is recessive it is the little ii. AB blood is codominant. Here is a blood cross Punnett square: Cross a man with
heterozygous B blood with a woman who is homozygous dominant A.
How can you get O blood – either cross 2 O parents or O will appear when crossing heterozygous parents.
B
i
I
A
I
A
I
A B
I I
A B
I I
A
I i
A
I i
18. Disorders will generally be told to you either in the story or in the picture/example. If it is dominant capital
letters, if it is recessive little letters.
19. Pedigrees show us who in families have a trait/disorder. We can determine genotypes by doing Punnett squares
& seeing which Punnett square has the same results as the family history. It shows us boy(squares)/girls
(circles), who has the trait/disorder, parents, children, marriages. Please be sure to review your symbols.