Presentation on theme: "Objective 7: TSWBAT explain how a lethal recessive allele can be retained in the population and why lethal dominant genes are much more rare."— Presentation transcript:
1 Objective 7: TSWBAT explain how a lethal recessive allele can be retained in the population and why lethal dominant genes are much more rare.
2 Lethal recessive alleles are maintained in the population because they are only lethal when homozygousHeterozygotes show no symptomsLikelihood of mating with another heterozygote is small and even is you do the likelihood of an affected offspring is ¼
3 Heterozygote advantage Being heterozygous confers an advantage on youExample is sickle cell anemiaHeterozygote has enhanced resistance to malariaLethal dominant genes are more rare because the effects are not masked in the heterozygoteMany are the result of mutations that subsequently the kill the developing organismIf symptoms do not appear until late in life, then there is a possibility of passing it on
4 Objective 8: TSWBAT describe how inheritance has its basis in the behavior of chromosomes during sexual life cycle.
17 The other two phenotypes (gray-vestigial and black-normal) were fewer than expected from independent assortment (and totally unexpected from dependent assortment).These new phenotypic variations must be the result of crossing over.