Chapter 13 Flashcards
incomplete dominance
each allele makes some contribution to the expression of a trait
heterozygous people have different traits than homozygous people
genotype ratio is the same as the phenotype ratio
multiple alleles
more than two for a gene are present in a population but an individual can only have 2 alleles
ABO blood groups in humans
3 alleles: code for production of carbohydrate on the surface of red blood cells
IA: codes for type A carbohydrate
IB: codes for type B carbohydrate
i: codes for no carbohydrate
IA and IB are codominant: both together are expressed when found together
i is recessive
geno and pheno blood type
ii: type o
IAIA or IAi: type A
IBIB or IBi: type B
IAIB: type AB
how can the carbohydrate be detected
by reactions with different antibodies
blood transfusions
antibodies are produced against carbohydrate types a person does not produces
Ex) a person with type A blood will produce atinbodies against the B carbohydrate
type AB: universal recipient
type O: universal donor
multiple genes
different genes code for proteins that contribute to the same character OR
there are multiple copies of the same gene in different locations on the chromosmes
skin color
caused by the production of melanin
2 alleles-dominant and recessive
3 copies of the gene
each copy of a dominant allele results in the production of more melanin
hair color
result of two pigements : 1. eumelanin-brown to black 2 alleles-dominant and recessive there are 4 copies of the gene on different chromosomes 2. promelanin 2 alleles-dominant and recessive 1 copy of the gene eumelanin masks the presence of promelanin
human disorders based on dominant/recessive alleles
most genetic disorders are recessive for the following reasons:
1. recessive alleles generally produce non fuctional proteins
many mutations can produce non functional versions of the same protien
2. dominant alleles mask the effect of the recessive alleles:
therefor: recessive alleles can be caried by indivduals and have no effect on their phenotype
they are difficult to eliminate from a population
examples of recessive allele disorders: cystic fibrosis
cystic fibrosis: excess mucus production
many mutations can cause the disease
1 in 30 people have a recessive allele
1 in 3600 people are homozygous recessive
examples of recessive allele disorders: tay-sachs disease
tay-sachs disease
liquid accumaltion in brain cells
common in some ethnic groups (up to 1 in 20 people carry recessive allele)
examples of recessive allele disorders: PKU
phenylketonuria (PKU): accumulation of phenylanaine (type of amino acid)
1 in 50 people carry the recessive allele
in dieases with incomplete dominance
the non- functional allele is usually rarer than dieseases of thr recessive alleles
disorders associated with dominant alleles
every affected person should have a parent with the disorder
dominant alleles are usually very rare in a population
usually associated with conditions that occur late in life
examples of dominant allele disorders: alzheimer’s disease
mental deterioration, especially memory
examples of dominant allele disorders: huntington disease
mental deterioration, muscle control
1 in every 20,000 people have the allele for the diease
frequency of alleles causing diease early in life
common to very rare
dominant/recessive
imcomplete dominance
dominant/recessive
independent assortment of alleles
pairs of alleles for gene separate independently of other alleles for other genes during gamete formation.
ex) YyRr produces
YR Yr yR yr
only occurs when the genes are on different choromsomes
linked genes
genes found on the same chromosome
crossing over seperate linked genes
the rate which gene are seperated depends on how far apart they are from one another
if genes are on the same chrosmosome (linked) then:
the phenotype conination on the parents will be the most commom combinantion in the offspring
- the ratio of phenotypes in across will be different from the ratio of unlinked genes
how do we find the location of genes
some chromosomeal mutations are associated with phenotypes and can be used to map genes onto chromosomes
2 ways sex can be determined genetically
- presence of sex chromosome
2. difference in the number of chromosomes
sex chromosomes XY system
males: one X abd one Y chromosome
females: two X chromosome
eggs cells all have an X chromosome, sperm will either have a X or Y
chromosome XY
Y chromosome is smaller than the X chromosome
Y chromsosome has gene which causes the dveelopment of testes (instead of overaies)
found in humans and many other animals
XO system
males: one X chromosome
females: two X chromsome
sperm have either X or no X chromosome
eggs cells all have X chromosome
found in some insects
ZW system
males: two Z chromosomes
females: one Z and one W chromosome
sperm cells all have a Z chromosome
eggs cells have a Z or a W chromosome
the W chromosome is smaller than the Z
found in birds, fish, and some insects
sex determineation by chromosome number
hapoid/diploid system
haploid/diploid system males: haploid females: diploid males develop from unfertilized eggs found in ants, bees, and termites
enviornmental induced sex determinartion
males and females are not genetically different
examples: temp affects sex determination in turtles
heraphrodites
males and females sex organs present in ech individual
common in plants, fungi, and simple animals
common organisms with limited access to mating partners
sex linked genes
found on sex chromosomes and not involved in determing the sex of an indivdual
ratios of phenotypes differ between males and females
XY system
X linked geens are more common than Y linked genes
males show higher occurance of recessive traits
ex) eye color is fruit flies
XR- dominant or red eye color
Xr recessive allele for white eye color
Y- non allele for eye color
general rules for X-linked
- males pass alleles to duaghters, not sons
- daughter of males with dominant trait will also have the dominant trait
- sons of females with recessive trait will also have the recessive trait
sex linked genes in humans
x- linked recessive traits - red/green color blindness
hemophilia -lack of blood clotting factor
occurs in 1 of every 10,000 males
1/3 of caes are due to spontaneous muations
