Lecture 14.b Flashcards
Epistasis
Effects of one gene are modified by one or several other genes. IF U DO NOT HAVE THE EXPRESSION OF BOTH, IT IS AS IF YOU DO NOT HAVE ANY OF THEM
ex. Allele of 1 locus can mask the expression of alleles of a different locus. (more common)
ex. Allele of 1 locus can enhance the expression of alleles of a different locus
Epistasis in human eye color
YOU NEED BOTH TO PRODUCE MELANIN
- make melanin
- OCA2 expressed
Albinism: an example of epistasis & pleiotropy?
epistasis: At least 5 different genes determine skin pigmentation BUT If you have the mutant gene for melanin production (gene not part of the 5 above)→ no skin pigmentation
pleiotropy: Missing melanin, so hair, skin, & eyes are light
Polygenic
traits are found along a continuum.
example of Polygenes
Height, weight, hair color, skin pigmentation, eye color
Polygenic inheritance:
multiple independent pairs of genes may have similar and additive effects on 1 phenotype.
Think paint mixing EACH GENE CONTRIBUTES TO THE FINAL RESULT
The “problem” with sex chromosomes?
Laws of segregation & independent assortment don’t always apply for 2 reasons
- Genes are linked: They’re on the same chromosome. no independent assortment.
- For genes on the Y chromosome: only 1 allele, not 2 alleles. Law of segregation doesn’t apply to linked genes
Females (XX) are __or __for all genes on the X chromosomes.
hetero
homozygous
Males (XY) are ___for all genes that they have only 1 copy of ie all the genes in the differential region of the X & Y chromosomes.
hemizygous
hemizygous meaning
an individual who has only one member of a chromosome pair or chromosome segment rather than the usual two.
why are Males more likely to express abnormal phenotypes ?
because they only have one copy of x chromosome.
how do males “compensate” their missing x chromosome
Male fruit flies have X chromosomes that are more “active”
In mammals, females have 1 X that is (mostly) inactivated in somatic cells
Only 1 of the 2 X chromosomes is expressed in each ___ of the female.
somatic cell
Barr body ?
an inactive X chromosome. It appears as a dense, dark-staining spot at the periphery of the nucleus of each somatic cell in the human female.
is the inactivation of x chromosome complete? how many genes are expressed?
Inactivation is not complete: ~29 genes are expressed: corresponds to genes in the homologous region
