8. Chromosomal Basis of Inheritance Flashcards
Thomas Hunt Morgan’s study involving Fruit Flies
What is a Wild-Type?
Most common character phenotype is wild type (i.e., red eyes)
What is a Mutant?
Less common character phenotype is mutant (i.e., white eyes)
What is a recombinant phenotype?
recombination leads to the creation of new combinations of alleles that were not present in either parent.
What is a linked gene?
(do not assort independently of each other)
Genes located near each other on the same chromosome are called linked genes since tend to travel together during meiosis and fertilization
– Such genes are often inherited as a set as crossing over between homologous chromosomes is very rare
What is an unlinked gene?
(assort independently of each other)
Genes that are not near each other on the same chromosome (or found on separate chromosomes), are called unlinked genes
– Such genes are not inherited together often as a set
– For genes that are far apart on the same chromosome, there is frequent crossing over that occurs (at prophase I) between homologous chromosomes
What is incomplete linkage?
Incomplete linkage refers to a situation where two genes are located on the same chromosome but are not closely linked or do not exhibit complete genetic linkage. In other words, incomplete linkage describes the occurrence of crossing over or recombination events between two genes on the same chromosome.
Why are males more likely to inherit sex-linked disorders compared to females?
Since males have only one X chromosome, any male receiving the recessive allele from his mother will express the sex-linked trait
– Therefore, males are far more likely to inherit sex-linked recessive disorders compared to females
Examples of human-sex linked disorders?
- Duchenne muscular dystrophy
- Hemophilia
- Hypertrichosis
What is non-disjunction?
Pairs of homologous chromosomes do not separate normally during meiosis (i.e., at meiosis I or II)
- Gametes contain two copies or no copies of a particular chromosome
- As a consequence of non-disjunction, some gametes receive two of the same type of chromosome and another gamete receives no copy
What is aneuploidy?
What is monosomy?
Monosomy is a genetic condition in which an individual has only one copy of a particular chromosome instead of the usual two copies. It is characterized by the loss of one entire chromosome from a pair.
Monosomy X or Turner’s syndrome (X0 or X-), which occurs once in every 2500 births
– Short stature, sterile, normal intelligence
What is trisomy?
Trisomy is a genetic condition in which an individual has three copies of a particular chromosome instead of the usual two copies. It is characterized by the presence of an additional chromosome in a pair.
Trisomy X (XXX), which occurs once in every 1000 live births (female)
– Healthy females with mild to severe symptoms of developmental delays (learning disabilities, delayed speech/ language development)
– Capable of reproducing (limited)
examples of human aneuploid conditions
- Down Syndrome
- Kleinfelters Syndrome
- Monosomy (Turner’s Syndrome)
- Trisomy X
- Jacob’s syndrome
What is Cri Du Chat?
One syndrome, cri du chat, results from a specific deletion in chromosome 5
- Symptoms:
– Distinct facial features (i.e., wide-set eyes, small head, small jaw)
– Severe cognitive, speech, and motor delays
– High-pitched cry like the sound of a distressed cat [due to larynx (i.e., voicebox) not developing correctly]
What is Duchenne muscular dystrophy
Affected individuals rarely live past their early 20s (affects 1 in 3,500 males in the USA)
-Disorder due to the absence of an X-linked gene for a muscle protein called dystrophin
– Dystrophin is part of a group of proteins (a protein complex) that work together to strengthen muscle fibers and protect them from injury as muscles contract and relax
- Characterized by progressive weakening of muscles
What is Jacob’s Syndrome?
Jacob’s syndrome (XYY – trisomy of sex chromosomes), occurs once in every 1000 live births (male)
– Occurs when male inherits two Y chromosomes from father instead of one
– Often are taller than average (which becomes
apparent at age of five or six) with an average final height approximately 7 cm (3”) above expected final height
– Often have below-normal intelligence (learning disabilities have been reported in up to 50% of cases, most commonly speech delays and language problems…reading difficulties are common due to an increased incidence of dyslexia)
– Males that are XYY are still able to have children
