PEDIGREES: Genetic Family Histories Women are represented with a ______. Men are represented with a ______. Affected individuals are shaded. Discuss with your table partner: In some cases, the family history can allow you to determine a person’s genotype (the 2 alleles possessed by the individual) in situations where you can not determine this from phenotype alone. Remember that each parent passes down one of their alleles to each offspring.
On the next slides determine any of the genotypes you can from the given information. And then try to describe two situations in which you can determine the genotype on the following slide.
Pedigree for short eyelashes. Long eyelashes are dominant (L). Short eyelashes is recessive (l).
What is the genotype of II-3? _____ What is the genotype of II-5? ____ What is the genotype of III-7? ____ You do not need to look at family history for an individual to determine genotype for a ______trait. The individual must be ______.
If an individual has the ______phenotype a family history may tell you the genotype. They are ______if they have o ______o ______Discuss with your table partner: Try the challenge question on the next slide.
To answer the question, review patterns of inheritance of X and Y chromosomes from father and mother to offspring.
Can it be determined from this pedigree if the PTC tasting gene is sex-linked (X chromosome) or autosomal? Must be ______. • ______• ______
Errors in Meiosis Nondisjunction is a failure of a chromosome pair to ______. This mistake causes the gametes to have an ______.
Recall that: • Homologous pairs separate during Meiosis I • Sister chromatids separate during Meiosis II Nondisjunction can occur in either meiosis I or Meiosis II. (The difference is that if it occurs in Meiosis I all the egg/sperm produced have an abnormal number.) Aneuploidy- the condition having an abnormal number of chromosomes.
When nondisjunction occurs half of the eggs/sperm produced will have 2 copies of the chromosome and half will not have the chromosome. (recall that gametes normally have one copy)
If the egg or sperm with 2 copies is fertilized, the resulting zygote (fertilized egg) will have __ copies of that chromosome. This type of aneuploidy is called ______.
If the egg or sperm with no copies of a chromosome is fertilized, the resulting zygote will have ______copy. This type of aneuploidy is called ______.
______is caused by trisomy 21. Overview Nondisjunction- the failure of a chromosome pair to separate during meiosis.
Leads to
Aneuploidy- an abnormal number of chromosomes (not a pair). Two types
Monosomy: only having Trisomy: having three one copy of a copies of a chromosome. chromosome.