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TRANSCRIPT
Incomplete and Co Dominance
& Sex Linked Traits
Mr. Fernandes
Review of Mendel’s Principles
Genes are passed parents offspring;
get one allele from each parent
During Meiosis, the alleles for a gene
segregate from each other.
During Meiosis, genes independently
assort with each other.
Exceptions to Mendel’s principles
Sometimes, there is no dominant or
recessive gene, or the trait is controlled
by many alleles or genes.
Karyotype: a picture of chromosomes
Body Cells vs. Sex Cells
Autosomes: the first 22 homologous pairs of chromosomes.
Autosomes are the same for both males and females.
Sex cells: Determine sex of offspring
Is it Male or Female? Explain
Sex chromosomes: determines the sex of the individual
The sex chromosomes are the 23rd pair of chromosomes.
XX =female
DAD
Why?
All moms have the genotype XX. When egg cells are made, they will all carry a single X chromosome.
All dads have the genotype XY. When sperm cells are made, 50% will have an X chromosome and 50% will have a Y chromosome.
Therefore, males and females are born in roughly a 50:50 ratio.
Which parent determines the sex of an offspring?
SEX-LINKED TRAITS
Those traits that are controlled by genes on the X or Y chromosomes.
NOTE: The Y chromosome is much smaller than the X chromosome and only contains a few genes. Most sex-linked traits are on the X chromosome.
In humans, hemophilia is a sex-linked trait. Having
hemophilia is recessive (Xh) to being normal (XH). The
heterozygous female is called a carrier. Cross a carrier
female with a normal male.
__ XHXh __ X __ XHY ___ XH Xh
XH
Y
XH XH
XH Y Xh Y
XH Xh
male
Now You Try
Cross a carrier female with a male with hemophilia.
__ XHXh __ X __ XhY ___
In Incomplete Dominance, every genotype has its own
phenotype. (One allele not completely dominant over the
other.) Third phenotype that is a blending of the parental
traits. (2 alleles produce 3 phenotypes.)
Result: Heterozygous phenotype somewhere in
between homozygous phenotype.
Incomplete Dominance
1. Incomplete Dominance
Examples:
Trait: Flower Color
Expressions: Red x
White Pink
RR= Red; RW= pink; WW=
white
straight hair, wavy, curly
Incomplete Dominance
In codominance, neither allele are dominant;
both are expressed. A cross between
organisms with two different phenotypes
produces offspring with has both phenotypes
of the parental traits shown.
Codominance
2. Codominance Both alleles contribute to the phenotype.
Example: In come chickens
Black Chicken x White Speckled Chicken
YOU tell me which type of
dominance…
Codominance!
Type of
Dominance?
Incomplete
Dominance!
Type of Dominance?
Incomplete Dominance!