Genetics and Heredity Part II. Is the study of genetics and heredity really as simple as 2 alleles and a Punnett square?. Unfortunately, NO. Darn . . . The following concepts make genetics more interesting and also more complicated:
Darn . . .
The following concepts make genetics more interesting and also more complicated:
- incomplete dominance
- multiple alleles
- polygenic inheritance
- environmental factors
- chromosome disorders
- sex-linked disorders
Incomplete dominance occurs when the offspring of 2 homozygous parents show an intermediate phenotype. (#6)
+ also more complicated:
RED WHITE PINK (RR) (WW) (RW)
Red and white are equally dominant colors also more complicated:
Second generation: red and white reappear
curly also more complicated:
Type of Hair
Many traits are controlled by multiple alleles. They produce 3 or more phenotypes.
Ex: also more complicated:blood types
3 alleles for blood
A, B, O
4 blood types:
A, AB, B, O
Polygenic inheritance occurs when a group of genes work together to produce one trait. #9
As a result, many phenotypes are produced. also more complicated:
These 3 gene pairs work together to determine one trait.
Ex: also more complicated: hair color, eye color, skin tone
Environmental Factors also more complicated:
Your environment may help determine which traits are expressed.
Ex: also more complicated:Your diet, exposure to chemicals or sunlight, and temperature can affect genetics.
Every species has a specific # of chromosomes.
Humans have 46 chromosomes or 23pairs.
Human Chromosomes also more complicated:
Pair #23 determines gender:
XX = girl
XY = boy.
Sometimes an error occurs during also more complicated:meiosis and a gamete (egg or sperm) has too many or too few chromosomes.
# of chromosomes ≠ 23
If the zygote survives, the baby will be born with a disorder or disability.
Down’s Syndrome: 3 copies of chromosome #21; short stature, oversized heart, learning disabilities
Turner syndrome: also more complicated:only affects girls; are missing part or all of one X chromosome; neck webbing, short, infertile, severe heart and kidney problems (#13)
Autism: also more complicated:brain disorder; repetitive movements, delays in speech, learning, and socialization
Marfan’s Syndrome: affects connective tissue; thin body, narrow face, long limbs
This girl is missing part of her also more complicated:18th chromosome.
This boy is missing part of the 11thchromosome. (Jacobsen’s Syndrome) (#13)
Sex-Linked Disorders also more complicated:
Some conditions are passed only on the 23rd or the X or Y chromosome.
Since these are our sexcells, the disorders are sex-linked.
All eggs carry the also more complicated:X chromosome. The sperm determines the gender of a child.
It’s a BOY!!
It’s a GIRL!!
If a disorder is carried on the Y chromosome, only boys can inherit it.
Punnett square for a sex-linked disorder that’s carried on the X chromosome.
Mother does not have the disorder, but carries and passes on the gene for it.
Duchenne Muscular Dystrophy the X chromosome.
Calico (cats’ fur)
Hemophilia the X chromosome.
This hemophilia patient received only one injection (shot).
The body reacted with severe bleeding under the skin. (bruising)
A pedigree is a chart used to trace genetic traits throughout a family’s history.
A pedigree is very useful when trying to find the the X chromosome.pattern of inheritance of a genetic disorder.
(colorblindness, baldness, hemophilia)