Chapter 13 - Human Genetics

Question 1

Morgan used fruit flies for his genetic research because they

Answer 1

1. short life cycle that lasts 10 days
2. Produce huge numbers of offspring
3. Contain four pairs of huge chromosomes
4. Are extremely inexpensive to maintain

Question 2

Parental phenotypes

Answer 2

Offspring are identical to the original P generation

Question 3

Recombinant phenotypes

Answer 3

Offspring have different combinations of traits from those of the P generation

Question 4

Morgan further hypothesized that linked genes in the test cross went through a

Answer 4

Chromosome recombination, which caused the recombinant phenotypes
In other words, there was a crossing over

Question 5

Alfred Stuart, an undergrad student of Morgan

Answer 5

Realized that recombination frequencies could be used map the locations of the genes on a chromosome
He determined that the recombination frequency of any two linked genes reflects the genetic distance between them on the chromosome.
The greater the distance between two genes, the greater the chance a crossover can form between the genes and greater recombination frequency

Question 6

X chromosome

Answer 6

Bigger than the Y because it contains over 20,000 genes

Contains the genes responsible for female development and genes responsible for non-sexual traits

Question 7

Y chromosome

Answer 7

Much smaller than the X chromosome because it contains few gene, including the SRY gene.
Early in embryonic development, structures that give rise to reproductive organs are the same in XX and XY embryos
When the SRY gene becomes active, parts of these structures develop as testes

Question 8

Deletion

Answer 8

Occurs if a broken fragment is lost
Example is the deletion of the end of human chromosome 5
Causes cri-du-chat disorder

Question 9

Duplication

Answer 9

Occurs if a fragment is transferred from one chromosome and inserted into its homolog
Example is the duplication of the genes for red blood cell production
Sherpas have excessive amount of red blood cells compared to the average person
Due to extra red blood cells, they get plenty of oxygen to all of their cells at high altitudes

Question 10

Inversion

Answer 10

Occurs if a fragment reattaches to the same chromosome in the reversed position

Question 11

Translocation

Answer 11

Occurs if a fragment is attached to a different, non-homologous chromosome
Most common effect of translocation is cancer

Question 12

In euploid organisms

Answer 12

Their cells contain the normal number of chromosomes

Question 13

In aneuploid organisms

Answer 13

Their cells contain an extra or missing chromosome

Question 14

In polyploid organisms

Answer 14

Their cells contain an extra set of chromosomes

Question 15

Edward Syndrome

Answer 15

Offspring born with an extra chromosome 18

Question 16

Parsi Syndrome

Answer 16

Offspring is born with an extra chromosome 13

Question 17

Down Syndrome

Answer 17

Offspring has and extra chromosome 21

Question 18

Turner Syndrome

Answer 18

Female offspring with only one X chromosome

Question 19

Jacob Syndrome

Answer 19

Male offspring with an extra Y chromosome

Question 20

Kinefelter Syndrome

Answer 20

Male offspring with an extra X chromosome

Question 21

Examples of autosomal recessive traits

Answer 21

Sickle cell
Cystic fibrosis
Phenylketonuria (PKU)
Yay-Sachs disease

Question 22

Examples of autosomal dominant disorders

Answer 22

Hypercholesteromia
Achondroplasia
Huntington’s disease
Neurofibromatosis

Question 23

X-linked recessive traits

Answer 23

Appear more frequently in males because males need to receive only one copy of the recessive allele on the X chromosome to develop that trait
Examples
Red-green color blindness
Hemophillia
Duchenne muscular dystrophy

Question 24

Examples of X-linked dominant disorders

Answer 24

Hereditary enamel hypoplasia

Constitutional thrombopathy

Question 25

Amniocentesis

Answer 25

Performed between 14 and 20 weeks of pregnancy

Question 26

Chorionic villus sampling

Answer 26

Performed as early as 8 weeks pregnant

Question 27

Genetic screening

Answer 27

Genetic screening is completed after the baby is born