Chapter 13 - Human Genetics Flashcards
Morgan used fruit flies for his genetic research because they
- short life cycle that lasts 10 days
- Produce huge numbers of offspring
- Contain four pairs of huge chromosomes
- Are extremely inexpensive to maintain
Parental phenotypes
Offspring are identical to the original P generation
Recombinant phenotypes
Offspring have different combinations of traits from those of the P generation
Morgan further hypothesized that linked genes in the test cross went through a
Chromosome recombination, which caused the recombinant phenotypes
In other words, there was a crossing over
Alfred Stuart, an undergrad student of Morgan
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
X chromosome
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
Y chromosome
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
Deletion
Occurs if a broken fragment is lost
Example is the deletion of the end of human chromosome 5
Causes cri-du-chat disorder
Duplication
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
Inversion
Occurs if a fragment reattaches to the same chromosome in the reversed position
Translocation
Occurs if a fragment is attached to a different, non-homologous chromosome
Most common effect of translocation is cancer
In euploid organisms
Their cells contain the normal number of chromosomes
In aneuploid organisms
Their cells contain an extra or missing chromosome
In polyploid organisms
Their cells contain an extra set of chromosomes
Edward Syndrome
Offspring born with an extra chromosome 18
Parsi Syndrome
Offspring is born with an extra chromosome 13
Down Syndrome
Offspring has and extra chromosome 21
Turner Syndrome
Female offspring with only one X chromosome
Jacob Syndrome
Male offspring with an extra Y chromosome
Kinefelter Syndrome
Male offspring with an extra X chromosome
Examples of autosomal recessive traits
Sickle cell
Cystic fibrosis
Phenylketonuria (PKU)
Yay-Sachs disease
Examples of autosomal dominant disorders
Hypercholesteromia
Achondroplasia
Huntington’s disease
Neurofibromatosis
X-linked recessive traits
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
Examples of X-linked dominant disorders
Hereditary enamel hypoplasia
Constitutional thrombopathy
Amniocentesis
Performed between 14 and 20 weeks of pregnancy
Chorionic villus sampling
Performed as early as 8 weeks pregnant
Genetic screening
Genetic screening is completed after the baby is born
