Types of natural selection: Different types of natural selection can impact the distribution of phenotypes within a population.In (a) stabilizing selection, an average phenotype is favored.In (b) directional selection, a change in the environment shifts the spectrum of phenotypes observed.In (c) diversifyingselection.
The sporophyte generation produces spores that grow into a GAMETOPHYTE.
Answer:
Each of her parents must have one recessive gene for blond hair color
Explanation:
- Blond is a recessive trait
- Since Silvia is blond this means she has both copies of the recessive gene for hair color
- Therefore, both her parents have a recessive gene for blond hair and passed it down to her.
- The parents don't have blond hair because their dominant gene for browns masks the recessive gene for blond.
Answer: Although both are X-linked recessive conditions, and therefore more likely in males, with the single X-chromosome. The recessive allele in colour blindness occurs at a higher frequency in the population and is a mild condition. Thus colour blindness does occur to a lesser extent in females because it needs the double recessive condition. DMD is a severe, disabling condition with a limited lifespan, and recessive allele frequency much lower, so the double recessive condition in females is very rare.
Explanation: DMD is an X-linked recessive, “nearly always in males” suggest that it also occurs due to a new mutation or some rare condition e.g. double recessive from an affected father and carrier mother, or inactivation of the normal gene in a heterozygote. It is also found that the defective allele is not completely recessive and that female carriers may exhibit mild to moderate effects.
colour blindness is polygenic, although the genes are all X-linked. It is more common in males than females. Females can carry two recessive alleles and so express the phenotype, but this is uncommon because the frequency of the recessive gene is low.
There are similarities in that both are X-linked recessives, therefore commonly expressed in males, who only have one X chromosome. The gene frequency of the colour blindness recessive is much higher than that of DMD, so the double recessive condition, which affects females, is more likely to be seen with colour blindness. In addition, DMD is a severe condition associated with disability and limited lifespan, which reduces the probability of mating between an affected male and carrier female
