GENETICS problem #35 (Explain solutions, please) Sex Determination and Sex-Linke
ID: 144454 • Letter: G
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GENETICS problem #35 (Explain solutions, please)
Sex Determination and Sex-Linked Characteristics 105 34. If the blue F, females in Figure 4.15b are backcrossed to the blue males in the P generation, what phenotypes and proportions of offspring will be produced? 35. Red-green color blindness is an X-linked recessive trait in humans. Polydactyly (extra fingers and toes) is an autosomal dominant trait. Martha has normal fingers and toes and normal color vision. Her mother is normal in all respects, but her father is color blind and polydactylous. Bill is color blind and polydactylous. His mother has normal color vision and normal fingers and toes. If Bill and Martha marry, what phenotypes and proportions of children can they produce? 36. A Drosophila mutation called singed (s) causes the bristles to be bent and misshapen. A mutation called purple (p) causes the fly's eyes to be purple in color instead of the normal red. Flies homozygous for singed and purple were crossed with flies that were homozygous for normal bristles and red eyes. The F, were intercrossed to produce the E and the following results were obtainedExplanation / Answer
Colour blindness is a usually a genetic (hereditary) condition. Red/green and blue colour blindness is usually passed down from your parents. The gene which is responsible for the condition is carried on the X chromosome and this is the reason why many more men are affected than women.
Polydactyly can occur by itself, or more commonly, as one feature of a syndrome of congenital anomalies. When it occurs by itself, it is associated with autosomal dominant mutations in single genes, i.e. it is not a multifactorial trait. But mutation in a variety of genes can give rise to polydactyly.
Autosomal traits are associated with a single gene on an autosome (non-sex chromosome)—they are called "dominant" because a single copy—inherited from either parent—is enough to cause this trait to appear. This often means that one of the parents must also have the same trait, unless it has arisen due to an unlikely new mutation.
Martha : normal vision and fingers/toes......her father is colourblind and hence she is the carrier of colorblindness trait.(XcX) Xc - represents carrier of colorblind trait.
Bill : colorblind(XcY) and polydactylous....his mother is normal.
therefore,
XcX x XcY
XcXc (colorblind daughter) XcY(colorblind son) XXc (daughter carrier of colorblind trait) XY (Normal son)
One copy of the autosome is shared from the father and hence there is a 50% chance of the progeny to be polydactylous.Hence the phenotypic ratio obtained is : 1:1:1:1
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