Download Inheritance Patterns and Human Genetics Review

1.
2.
3.
4.
5.
6.
7.
Biology 30
Inheritance Patterns and Human Genetics Review (68 marks)
How does the inheritance of sex chromosomes result in approximately equal
numbers of males and females among the offspring of fruit flies? (2 marks)
The male sex chromosomes are X and Y. One half of the male gametes will
contain an X chromosome and one-half will contain an Y chromosome; the
number of male offspring and the number of female offspring are
approximately equal as a result
Offer an explanation for why Morgan did not find white-eyed females in the
F2 generation when he crossed white-eyed males with red-eyed females. (2
marks)
The mutant allele is X-linked, so a female must have two copies of the
mutant allele to get white-eyes
How does crossing over show that genes are found on chromosomes? (2
marks)
Traits known to be controlled by genes on the same chromosome are
normally inherited together so a 3:1 phenotypic ratio will be created. But a
different ratio can indicate separation has occurred.
How can crossing over between two alleles be used to map their location on
chromosomes? (2 marks)
The farther apart two alleles are on a chromosome, the more often they will
be separated by crossing-over thus the more they will be appear in new
combination
What are point mutations? (3 marks)
A point mutation is the substitution, addition or removal of a single
nucleotide within a segment of DNA
Biologists have observed that chromosome mutations often occur during
nuclear division. Why do you think this is so? Explain your answer.(2 marks)
Just before nuclear division, chromatin condenses to form chromosomes,
which move through the cell during the different phases of nuclear division
so they are at a higher risk of breakage.
A husband and wife are heterozygous for cystic fibrosis. Their son has
cystic fibrosis. Their second child, a daughter does not. Prepare a pedigree
for this family. (5 marks)
or
8. A husband and wife have the ABO blood group genotypes IAIB and ii. What
ABO blood types can their children have? (4 marks)
Their children will be type A or type B
IA IB
i
IAi IBi
i
IAi IBi
9. Compare the inheritance of Huntington’s disease with the inheritance of
sickle cell anemia. (4 marks)
Huntington’s disease is inherited as a dominant autosomal allele. Anyone who
inherits the allele for HD will have the disease.
Sickle-cell anemia is inherited as a recessive autosomal allele. A person who
is heterozygous for sickle-cell anemia is a carrier of the disease but to get
it a person has to have two recessive traits.
10. Is pattern baldness a sex-linked trait or a sex-influenced trait? Explain
your answer. (2 marks)
Pattern baldness is a sex-influenced trait because it is controlled by an
autosomic allele but expressed differently in males and females due to the
presence of different sex hormomones.
11. How can nondisjunction change chromosome numbers? (2 marks)
Nondisjunction can produce gametes with either one too few or one too many
chromosomes. If such a gamete is fertilized a monosomic or trisomic
individual can result.
12. Colorblindness is rare among females. Why? Explain your answer.(2 marks)
Colorblindness is an X-linked recessive trait, so for a female to have this
disorder she would have to have two recessive genes for it to be expressed
but males only need one gene for it to be expressed.
13. What evidence led Morgan to hypothesize that the gene for eye color in
Drosophila is carried on the X chromosome? (3 marks)
Morgan crossed a heterozygous red-eyed female with a red-eyed male and
noticed all the females had red eyes but ½ of the males had red eyes and
half had white eyes. This could only occur if the trait was carried on the X
chromosome.
14. Why is hemophilia carried by females but expressed in males and rarely in
females? (4 marks)
Hemophilia is an X-linked recessive disorder. Therefore, females would have
to inherit two copies of the allele in order to express the disease. Males are
affected by inheriting just one copy of the gene.
15. What is a linkage group? How many linkage groups do humans have? (2
marks)
A linkage consists of all the genes on a pair of homologous chromosomes.
Humans have 23 linkage groups.
16. How does a chromosome mutation differ from a point mutation? (4 marks)
A chromosome mutation is either a change in the structure of a chromosome
or the loss of an entire structure.
A point mutation involves the substitution, addition or deletion of a single
nucleotide.
17. What is a genetic marker? (2 marks)
A genetic marker is a short segment of DNA that is known to have a close
association with a particular gene of interest located on a nearby
chromosome.
18. Distinguish between germ-cell mutations and somatic mutation. (2 marks)
Germ-cell mutations occur in the gametes and affect the zygote. Somatic
mutations take place in the body cells and are not passed on to the
offspring.
19. Distinguish between multiple allele traits and polygenic traits. (2 marks)
Multiple allele traits are controlled by three or more alleles of the same
gene that code for the same trait.
Polygenic traits are controlled by two or more different genes controlling
the same trait.
20. Explain how you distinguish the karyotype of a normal human male from that
of a human male with Down syndrome. (3 marks)
Normal male  22 homologous pairs of chromosomes and a XY pairing
Down Syndrome  21 homologous pairs, 3 chromosomes in position 21 and a
XY pairing.
21. Distinguish between amniocentesis and chorionic villi sampling. (4 marks)
In amniocentesis, a small amount of amniotic fluid is removed at some time
during the 14th and 16th weeks of pregnancy; fetal cells and proteins in the
fluid are analyzed and a karyotype created.
Fetal cells from chorionic villi sampled are also obtained but during the 8th
and 10th week of pregnancy. A karyotype is also prepared from the grown
cells.
22. Describe the difference between a sex-linked trait and a sex-influenced
trait. (2 marks)
A sex-linked traits is controlled by a gene that is found only on one sex
chromosome.
A sex-influenced trait is expressed differently in men and women who have
the same genotype for the trait due to the affect of sex hormones.
23. In Drosophilia the genes for body color and wing length are on the same
chromosome. Gray body is dominant to black body and long wings are
dominant to short wings. Assume that both dominant alleles are on the same
chromosome. Draw a Punnett square representing the cross between two
heterozygous individuals. Write the phenotypic and genotypic ratios that
would be expected among the offspring, assuming that crossing-over does
not occur. (6 marks)
Gray body – G
Black body – g
Long wings – L
Short wings – l
Heterozygous gray body, X
heterozygous gray body,
Long wings
long wings
GgLl
GgLl
GL
gl
GL
GGLL
GgLl
gl
GgLl
ggll
Genotypic ratio  1 GGLL: 2 GgLl: 1 ggll
Phenotypic ratio  3 gray body, long wings: 1 black body, short wings
24. Describe how the karyotype of an XXY human would differ from that of an
XO human. (2 marks)
XXY karyotype would have three sex chromosomes so a trisomy.
XO karyotype would have only one sex chromosome so a monosomy.