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Genetics

Non-Mendelian inheritance patterns include incomplete dominance, codominance, multiple alleles, lethal alleles, and gene interaction. In incomplete dominance, the heterozygote phenotype is intermediate between the two homozygotes. Codominance occurs when both alleles are fully expressed. Multiple alleles exist when more than two alleles control a trait. Lethal alleles cause death. Gene interaction includes epistasis, where one gene masks another, and novel phenotypes from two interacting genes. X-linked genes are found on the X chromosome and typically affect males more than females.

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42 views2 pages

Genetics

Non-Mendelian inheritance patterns include incomplete dominance, codominance, multiple alleles, lethal alleles, and gene interaction. In incomplete dominance, the heterozygote phenotype is intermediate between the two homozygotes. Codominance occurs when both alleles are fully expressed. Multiple alleles exist when more than two alleles control a trait. Lethal alleles cause death. Gene interaction includes epistasis, where one gene masks another, and novel phenotypes from two interacting genes. X-linked genes are found on the X chromosome and typically affect males more than females.

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Angela Balmes
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NON-MENDELIAN INHERITANCE a diploid individual has at most 2

homologous gene loci which may be


Incomplete Dominance occupied by different alleles of the same
Codominance gene
Multiple Alleles example:
Lethal Alleles ABO blood group
Gene Interaction A = B > O which means that blood
Epistasis types A and B are dominant while
Novel Phenotypes blood type O is recessive
X-linkage Many different genotypes are possible
Sex Limited and Sex Influenced Gene
GENOTYPE ANTIGEN PHENOTYPE
Incomplete Dominance
no dominant trait AA, AO A A
blending of characteristics between the
parents BB, BO B B
the phenotype of the heterozygote is AB A,B AB
intermediate between those of the two
homozygotes OO NEITHER O
example:
Four oclock plant white loci in fruit flies
3 different flower colors- red, pink, fur color in rabbits
white
Lethal Genes
Complete Dominance causes death of the organism
both alleles are dominant a corresponding homozygous gene will
cause death to the organism
no recessive gene
one or both can be expressed may be dominant or recessive
example: example:
MN blood group: blood type M, N, or MN colors of mouse
-characterized by an antigen called a 2 colors- agouti and yellow
glycoprotein, found on the surface of red a homozygous yellow genotype
blood cells (ATAT) causes death
Legend: Huntingtons disease
MN X MN also called Huntingtons chorea,
chorea major, or HD
1 MM: 2 MM: 1 MN
M- M Glycoprotein a genetic neurological disorder
characterized by abnormal body
N- N Glycoprotein
movements called chorea and a lack of
MN- M & N Glycoprotein are present
coordination
affects a number of mental abilities and
M N some aspects of behavior
M MM MN name is derived from the physician
George Huntington who described the
N MN NN disorder in 1872

Gene Interaction
Multiple Alleles
occur when genes influence a particular
the number of alleles that can be characteristic
expressed is more than two
two types:
can only be studied in populations Epistasis
expression of one gene or gene pair Sex Limited Genes
masks the expression of another gene or autosomal genes whose expression is
gene pair in another loci manifested only in one sex because of
epistatic gene- affects other genes physiological and anatomical conditions
hypostatic gene- gene that is affected example:
examples: neck and tail plumage in domestic fowls
Bombay phenotype in ABO blood
groups Sex-influenced traits
modifies the expression of the ABO the sex of the individual influences the
blood group expression of a trait that is not limited to
first recognized in a woman in one sex
Bombay example:
the presence of the homozygous Baldness
recessive (mm) genotype only GENOTYPE PHENOTYPE
expresses blood type O
the presence of the homozygous Female Male
(MM) or heterozygous (Hh)
phenotype allows normal expression BB Bald Bald
of blood type Bb Not Bald Bald
coat color in mice
B_C_- agouti B_cc- albino bb Not Bald Not Bald
bbC_- black bbcc- albino
Novel Phenotype
occurs when 2 genes affect each other
example:
squash
A_B_- disc-shape A_bb- sphere
aaB_-sphere aabb- long
comb in chickens

X-linked genes
genes found in the X-chromosome
example:
Color blindness
Legend:
Xc- color blind
XC- normal eye vision
XCXc X XCY
Phenotypic ratio
1 color blind male: 1 normal male: 2
normal female
XC Xc

XC XCXC XCXc

Y XCY XcY
Eye color in Drosophila

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