non-mendelian genetics
DESCRIPTION
Non-Mendelian Genetics. When Heredity Follows Different Rules. Incomplete Dominance. Incomplete Dominance – the phenotype of heterozygous individuals is intermediate to the homozygotes NEITHER allele is dominant over the other so they MIX together Example: - PowerPoint PPT PresentationTRANSCRIPT
Non-Mendelian Genetics
When Heredity Follows Different Rules
1. Incomplete Dominance – the phenotype of heterozygous individuals is intermediate to the homozygotes
a) NEITHER allele is dominant over the other so they MIX together
2. Example:a) Homozygous R snap-dragons are RED (RR)b) Homozygous R’ snap-dragons are WHITE (R’R’)c) A cross between these two parents will result in all heterozygous
snap-dragons, which are PINK (RR’)d) A cross between two pink heterozygotes results in a 1:2:1 ratio
of phenotypes
Incomplete Dominance
Complex Genetics – Incomplete Dominance
1. The dominant allele is not completely dominant over the allele.
2. Result: a blend of the 2 forms of the trait.
1. R – red flower2. R’ – white flower
3. RR – red4. R’R’ – white5. RR’ - pink!
RR R’R’
RR’RR’RR’RR’
RR
R’R’
RR’ R
R’
R R’
RR RR’
RR’ R’R’
P
(All pink)
Codominance1. Codominance – BOTH alleles are dominant so BOTH
phenotypes are present in heterozygous individualsa) Alleles do NOT MIX; both are equally present
2. Example:a) Homozygous B chickens are BLACK (BB)b) Homozygous W chickens are WHITE (WW)c) Heterozygous chickens are BLACK AND WHITE (BW) in
a checkered patternd) A cross between two checkered heterozygous chickens
results in a 1:2:1 ratio of phenotypes
Complex Genetics – Co-Dominance1. There are 2
dominant alleles for the trait.
2. Result: Both show up equally.
1. Ex. B – black feathers
2. W – white feathers
3. BB – black feathered chicken
4. WW – white feathered chicken
5. BW – black & white checkered feathered chicken!
Both are dominant allels and will display in the offspringWW X BB=BW
BB
WW
BW B
W
B W
BB BW
BW WW
P
(All checkered)
Sex Determination1. Humans have a diploid number of 46 chromosomes in 23
pairs
2. 22 of those pairs are called AUTOSOMES and are the same between males and females
3. The 23rd pair are the SEX CHROMOSOMES and are indicated by the letters X and Y
4. Males – XY5. Females - XX
Y = PENIS !The sperm (father) always determines the sex of the offspring
50%
Sex Chromosom
es
Sperm
Egg
XY
XXXX
XY
XX
XYXX
XY
Sex-linked Inheritance1. Sex-linked traits – traits which are controlled by a gene on the X
chromosomea) Inherited differently in males and females
2. The Y chromosome does not carry any genes to override the homologous gene on the X chromosome
a) Males have the trait more often because they don’t get a second X to override a recessive gene on the first X chromosome (males cannot be carriers)
b) Females still need TWO copies of the recessive gene to exhibit the recessive phenotype (females can be carriers)
3. Colorblindness4. Hemophilia – bleeding disorder causing your blood not to clot
properly
X-Linked Traits1. The allele is attached
to the X chromosome.
2. Can only be passed from Mother to son, Mother to daughter, or father to daughter.
X-linked genes means…1. Girls can be normal or
Carriers but Boys will be AFFECTED the most.
X Y
X XX XY
X XX XY
XH = normal visionXh = colorblind
Y = no genesXH
Xh
XH
Yx XH
Xh
XH
Yx
XH
XHNormal Female
Xh
XHFemale Carrier
YXHNormal Male
YXhColorblind Male
Female Carrier Normal Male
Hemophilia X-Linked
Lacks clotting in the blood
Menkes DiseaseX-linked gene causes kinky hair and mental disorders