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Incomplete Dominance. One allele is not completely dominant over another. Incomplete Dominance.
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Incomplete Dominance • One allele is not completely dominant over another
Incomplete Dominance • A flower has genes for white petals (w) and red petals (r). When you mix white flowers with red flowers you get pink flowers. How is this possible? The w gene does not dominate over the r gene and vice versa. Both genes express themselves equally so you get a pink color in the petals.
Codominance • Both alleles contribute to the phenotype
Polygenetic Traits • Traits controlled by two or more genes
Incomplete Dominance • RR x WW where RR is red and WW is white R R W W
Incomplete Dominance • RR x WW where RR is red and WW is white • Offspring RW are pink R R W W
Co-Dominance • RR x WW where RR is red and WW is white R R W W
Co-Dominance • RR x WW where RR is red and WW is white • Offspring RW show red and white: ex. Red Roan Horse R R W W
There are traits that are controlled by one gene with 2 alleles. Often, one is dominant and the other is recessive • Example: widow’s peaks and dimples.
Some traits are controlled by a gene with multiple alleles – 3 or more for a single trait. For example: blood types and skin color in humans.
There are 44 chromosomes that we call autosomal chromosomes. • However, there are 2 chromosomes that determine our sex and we call them sex chromosomes. • These 46 chromosomes all carrier genes on them that determine our traits.
Out of our 23 pairs of chromosomes, 1 pair is the sex chromosomes (X and Y). • Female = XX • Male = XY
Question: What is the probability that your parents will have a boy or girl? • XY (dad) x XX (mom) Y X Phenotype: 50% boy 50% girl X XX XY Genotype: 50% XX 50% XY X XX XY
Question? If my parents have 5 boys in a row, what is the chance they will have a girl the next time? 50%
Sex-linked gene: • Some traits are carried on the sex chromosomes. Genes on the X or Y chromosomes are sex-linked genes. • These traits are passes on from parent to child. Sex- linked genes can be recessive or dominant. • MALES are more likely to have a sex-linked trait because they only have ONE X and Y. The allele is USUALLY on the X chromosome. • Ex. colorblindness, hemophilia, hairy ears, muscular dystrophy
Are you colorblind? What numbers do you see?
Carrier – person who has one recessive allele and one dominant allele for a trait or heterozygous for that trait (only women can be carriers). Example Hemophiliac carrier XHXh Colorblind carrier XBXb
Sex linked Punnett Squares: Question: What is the probability that a carrier female and a colorblind male will have a girl who is colorblind (b = colorblind, B = normal)? Xb Y Phenotype: 25% normal boy 25% colorblind boy 25% normal girl 25% colorblind girl XBXb XBY XB Xb XbXb XbY
Try this one on your own Question: What is the probability that a homozygous (normal vision) female and a colorblind male will have a girl who is colorblind (b = colorblind, B = normal)?
Parents: XBXB x XbY Xb Y Phenotype: 50% normal girls 50% normal boys XBXb XBY XB XB XBXb XBY