1. HONORS Biology B_4 Heredity Additional Info
(B-4.5-8) Demonstrate an understanding of the molecular basis of heredity.
Website with good review images

2. Gamete Production In males — spermatogenesis produces 4 haploid sperm
46XY
In males — spermatogenesis produces 4 haploid sperm
In females — oogenesis produces
1 haploid egg (ovum), 3 polar bodies
23 X
23 X
23 Y
23 Y
46XX
23 X

3. Test Cross
A test cross is a way to determine the genotype of an organism with an unknown genotype.
Cross unknown with known.

4. X-Inactivation
Females (XX) carry twice as many X-linked genes as males (XY)
To correct this imbalance, in female mammals, cells have a system to ensure ONLY 1 copy of most the X-linked genes are active (turned “on”)  X chromosome Inactivation.
This ensures that men and women have equal X-linked genes controlling body growth, development, and functioning.
X-Inactivation occurs very early in embryonic development – one of the X chromosomes shortens so that most of the genes are not able to be read (Barr Body).
The process is random so the female body cells have a mixture in regards to which X is activated (can be different in identical twins). Only occurs in body cells.
EXAMPLE: Calico Cats

5. Epistatic Genes
Gene that determines whether or not a trait will be expressed.
Epistatic gene interferes with the expression of an other gene and can suppress/mask other gene.
Example: When the gene for albinism occurs the gens for skin color are not express (but are present).

6. Polyploidy
Polyploidy is common among plants, as well as certain groups of fish and amphibians.
What is it: Condition of possessing more than two complete sets of chromosomes.
How does it happen: Arise from nondisjunction during gamete formation (causing gametes to be diploid)… Fertilization between two diploid gametes results in tetraploids.
Different species show different levels of tolerance for polypoidy:
Highly frequent in flowering plants
Frequent in some species of fish and frogs
Not very frequent in higher vertebrates like humans