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:
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Darn . . .
- 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)
RED WHITE PINK (RR) (WW) (RW)
Second generation: red and white reappear
Type of Hair
Many traits are controlled by multiple alleles. They produce 3 or more phenotypes.
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
These 3 gene pairs work together to determine one trait.
Your environment may help determine which traits are expressed.
Ex: 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.
Pair #23 determines gender:
XX = girl
XY = boy.
Sometimes an error occurs during 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: only affects girls; are missing part or all of one X chromosome; neck webbing, short, infertile, severe heart and kidney problems (#13)
Autism:brain disorder; repetitive movements, delays in speech, learning, and socialization
Marfan’s Syndrome: affects connective tissue; thin body, narrow face, long limbs
This boy is missing part of the 11thchromosome. (Jacobsen’s Syndrome) (#13)
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 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.
Calico (cats’ fur)
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 pattern of inheritance of a genetic disorder.
(colorblindness, baldness, hemophilia)