Download PGS: 274 – 284

Chromosomes and Inheritance – Part 1
I.
Walter Sutton and Theodor Boveri
A. They developed the Chromosome Theory of Inheritance. (1902)
1. This theory states that genes have specific loci on chromosomes.
2. Each chromosome moves independently during segregation.
a. This theory supports Mendel’s Law of Segregation.
II.
Linked Genes
A. This term is usually for referring to genes found on the Autosomes (1 – 22). These are usually inherited as a
LINKED unit because they are found on the same chromosome.
B. Genetic Recombination occurs at Crossover in Prophase I when chromosome segments are exchanged
between homologous paired chromosomes. (Fig: 15.6)
1. Parental types – These offspring organisms look like the parents. (Fig: 15.5)
2. Recombinant types – These offspring organisms look like a combination of both parents because
of crossing over occurring.
III.
Alfred Sturtevant
A. He was the pioneer of genetic mapping – locating the loci of genes.
B. Cytological Maps
1. These maps locate genes loci base on banding stain pattern. (Fig: 15.15)
IV.
Sex-Linked Genes
A. This term refers to genes found on the sex chromosomes; 95% of the time it mainly refers to the X
chromosome. (Think X when it is seX linked.)
1. This is because both sexes have at least one X chromosome in their genome.
2. XX (Female and homologous) ; XY (Male and heterologous)
B. Sex chromosomes undergo very little crossover during Prophase I of Meiosis.
C. Sex of the organism will be determined at conception. (This is when egg is fertilized by the sperm. You will
either get a sperm containing an X chromosome or a sperm containing a Y chromosome.)
D. Everyone starts out female. (This is why we all have nipples.)
1. At about two months of age in the womb, the Y chromosome’s SRY gene goes active to make
testosterone to finish development of the male.
2. After development is complete, testosterone production is turned off until puberty. At puberty it is
turned back on so as to make the secondary sexual characteristics, such as facial hair.
E. Patterns of Inheritance and some Human Sex-Linked GENETIC Disorders: (NO cure exists, because the
problem is in the DNA.)
1. Color Blindness
a. This is the result of a faulty gene (recessive) on the X chromosome for making a particular
type of color absorbing protein in cones of the retina of the eye.
b. The most common type is Red/Green Colorblindness. (Red and Green appear gray.)
2. Hemophilia (Means “love of bleeding”)
a. These individuals cannot make Anti-hemolytic Factor. (AHF for short.)
b. They experience problems with bleeding to death.
c. This was a disorder associated with the “Royal Blue-Bloods of Europe” – They were
inbreeding to keep the crown “ In the Family”.
d. Treatment? These individuals have to keep AHF with them at all times in case they get
hurt. If they do get hurt and start to bleed they will require a shot of AHF to stop the
bleeding. Even a bruise (bleeding under the skin) can possibly lead to death.
3. THE PATTERN ON A PEDIGREE: It will appear to mainly affect males (as they only have
one X chromosome). This is because if the inherited X chromosome has a recessive gene on it; it
will not be covered up by a dominant one on another X chromosome (as is the case in most
females). Females can still get these disorders, but they must inherit TWO recessive X
chromosomes. The females tend to be CARRIERS, so they appear unaffected. So they tend to
pass the recessive X on to their sons. The son will be a SUFFEROR, if he gets the recessive X, of
the disorder. IT APPEARS TO SKIP A GENERATION, because the mother is a carrier and the
sons are showing the disorder.
V.
X Inactivation (Turning “off” one of the X chromosomes.)
A. This ONLY occurs in females because females have two X’s (Males only have one and it MUST remain
active.)
B. A Barr body is formed (From condensing one of the X chromosomes) to inactivate one set of information.
1.
The Barr body will be located on the nuclear envelope. (Criminal Forensics? This is how they
can tell the sex of the suspect. Males do not have them on their nuclear envelope.)
C. Mosaicism (Fig: 15.11) (A Mosaic is a puzzle.)
1. In humans, it is called “Complex Skin”. (Dry spots from mom’s X chromosome mixed with
Sweaty “Greasy” spots from dad’s X chromosome.)
2. Facial products is a Billion Dollar Industry as it only affects females, who tend to be VERY
concerned with their facial appearance and types of makeup that “Work” on their “skin type”.
Chromosomes and Inheritance – Part 2
I.
Chromosomal Errors than can occur:
A. These could occur during Mitosis OR Meiosis.
1. They would occur during the Anaphase Stages where Chromosomes are moving.
2. They could also occur during Crossover where gene DNA segments are moving.
B. Two types of errors can occur:
1. Chromosomal Number (Aneuploidy means “Abnormal number of chromosomes”)
a. This is the result of non-disjunction. (Failure to separate during Anaphase.)(Fig: 15.12)
b. Trisomic (Three of 1 KIND of chromosome.) (Fig: 15.15)
c. Monosomic (Missing one, the other half of the pair.) (It is located in the Trisomic gamete.)
d. Polyploidy (Many EXTRA SETS of chromosomes.)
i. 3n (triploid) Three “halfs” are in this cell.
ii. 4n (tetraploid) Four “halfs” are in this cell.
iii. Deadly in most animals; Plants not really affected because they are simple organisms.
2. Individual Chromosome Structure (Fig: 15.14)
a. These occur because of faulty crossover
b. Deletion – Chromosome segment is “missing”. It got stuck on the other homologous
chromosome during crossover.
c. Duplication – A chromosome segment was “copied” twice. (Two genes on one
chromosome. It is “missing” from the other homologous chromosome.)
d. Inversion – A chromosomal segment is “backwards”. It was inverted backwards during
crossover.
e. Translocation – A chromosomal segment is attached to a different autosome. It
accidentally broke loose and ended up on another chromosome.
II. Syndrome
A. This term refers to an organism “possessing” the identifying traits of a particular genetic disorder.
B. Human Genetic Disorders due to two abnormal chromosomal number (#) or structure:
1. Down’s Syndrome ( # )
a. This affects about 1 in 700 births.
b. This individuals possess an Extra 21 Autosome (A.K.A. Trisomy 21)
c. General syndrome features (Fig: 15.15)
d. Mainly the result of women of advanced age having babies.
2. Turners Syndrome (XO) ( # )
a. General characteristics: These individuals appear fairly normal. They just are lacking the
“sexual” characteristics we normally see in individuals. The “sexual” traits are
missing because there is NO second SEX chromosome to help create those traits.
These individuals are usually raised as females.
III. Extranuclear DNA (“extra” means “outside of”)
A. DNA that is located outside the nucleus in organelles. (These are Mitochondria, Chloroplasts, and Plastids.)
B. Mitochondria inherited from the mother inside the egg. (They are exactly alike.) (Helps in Criminal Forensics
cases trying to establish relationship between individuals.)
C. Mitochondrial Myopathy (These Mitochondria lack the ability to make large quantities of ATP because they
posses faulty DNA for making some of the enzymes in the cellular respiration process.)
1. General Characteristics: These individuals are very tired ALL the time.
REMEMBER THERE ARE NO CURES FOR ALL OF THESE DISORDERS ONLY TREATMENTS BECAUSE THE
PROBLEM IS GENETIC!