Unit 1 (Part 3 - Beyond Mendel’s Law of Inheritance!): Flashcards
Complete dominance
One allele is completely dominant over the other
Incomplete dominance
Heterozygote shows an intermediate, blended phenotype
E.g.
RR = red flowers
rr = white flowers
Rr = pink flowers
P.S. in a genetics problem, use the same letter conventions. However, add that the heterozygote is pink (in this case).
Codominance and multiple alleles for one trait
- 2 alleles affect the phenotype equally and separately (not a blended phenotype)
E.g. the human AB blood type is codominant, because it produces both type A and B antigens.
Possible blood types (phenotypes and genotypes)
Phenotypes:
A, B, AB, O
Genotypes:
AA, AO, BB, BO, AB, OO
P.S. AB is codominant. O is recessive.
Antigens on RBC for each blood type phenotype
Antibodies in blood for each blood type phenotype
A: type-A antigens on surface of RBC
B: type-B antigens
AB: both type-A and type-B
O: no A or B antigens
A: anti-B antibodies
B: anti-A antibodies
AB: not anti-A or anti-B antibodies
O: anti-A and anti-B antibodies
Donation status for each blood type phenotype
A: N/A
B: N/A
AB: universal recipient
O: universal donor (anyone can receive an O blood type)
Pleiotropy
One gene affects more than phenotypic characteristic (so it’s not just one part of the body that’s affected, it’s many parts)
Most genes are pleiotropic.
Examples of pleiotropy
- Dwarfism
- Gigantism
- Sickle cell anemia
Polygenic inheritance
Some phenotypes determined by additive effects of 2 or more genes on a single character.
How can you tell? Phenotypes on a continuum, as in there are a large scale of phenotypes, many different possible ones.
Polygenic inheritance examples
- Skin color
- Height
- Weight
Epistasis
(A type of polygenic inheritance)
One gene controls the expression of another gene.
Sex-linked traits
Usually means X-linked
Genes that are carried on sex chromosomes (as opposed to autosomal chromosomes)
Use mouse coat color to explain epistasis
Sex chromosomes
The sex chromosomes (X and Y chromosomes) determine whether an individual is male or female and are not considered autosomal chromosomes
Y chromosomes
Few genes other than SRY
- Turns of genes for production of male hormones, such as testosterone
X chromosome
Has other genes/traits beyond sex determination
X-inactivation
Female mammals inherit 2 X chromosomes.
X inactivation is a process by which one of the copies of the X chromosome is inactivated in therian female mammals during embryonic development (therian is an animal classification)
Meaning of the following pedigree chart symbols: empty square, empty circle, filled in square/circle, square and circle connected with a line.
- Male
- Female
- Affected individual
- Mating
