genetics ch8 pt2

1. what is this diagram depicting? 

1. a loop due to duplication

1. what can unequal crossing over lead to? 

duplications

1. what are double barred eyes and what caused them? 

1. caused by gene duplication 

2. drastically reduced eye size in drosophila

1. gene duplication causes effects through __________ _________ __________. 

1. altered gene dosage

1. what is altered gene dosage?

1. organism that has more or less than normal number of copies of particular gene

1. are all duplications bad? 

1. NO!

2. example: the globin gene family

1. globin gene family and relation to duplications: 

1.  expanded through duplications

2. early globins split into myoglobin, hemoglobin, neuroglobin → all have different functions

3. while oftentimes, consequences of duplication can be bad, this duplication allows flexibility to adapt to extreme environments 

1. how do you detect deletions? 

1. look for loops during prophase I that show normal chromosome looping

1. What are these diagrams depicting? 

1. deletion, looping of normal chromosomes

1. effects of deletions: 

1. may skew gene dosage

2. heterozygotes may have mutant recessive allele on normal chromosome, which now is unmasked in its expression (pseudodominance) 

3. some genes must be present in two copies for normal function (haploinsufficient genes)

1. pseudodominance? caused by? 

1. recessive trait is expressed and mimics a dominant inheritance pattern due to deletion 

1. haploinsufficient genes? can be caused by? 

1. genes where a single functional copy is not enough to maintain a normal phenotype 

2. loss of one copy leads to a disease or abnormal trait 

3. can be caused by deletion

1. what can deletions in humans cause? 

1. Cri-du-chat syndrome

2. Wolf-Hirschhorn syndrome

3. Williams-Beuren syndrome

1. characteristics of Cri-du-chat syndrome: 

1. small head

2. wide spaced eyes

3. cat-like cry as infant

4. mental retardation

1. characteristics of Wolf-Hirschhorn syndrome: 

1. seizures

2. mental and growth retardation

1. characteristics of Williams-Beuren syndrome:

1. heart defects

2. high blood pressure

3. cognitive impairments

1. what does inversion depend on? 

1. involvement of the centromere in the inversion 

2. paracentric → no centromere

3. pericentric → includes centromere

1. what is paracentric inversion? 

1. doesn’t include the centromere

1. what is pericentric inversion? 

1. includes the centromere

1. what is position effect? (what is it caused by, result)

1. inversions or translocations move a gene

2. if positions are altered, genes can be expressed at wrong times and in wrong tissues

3. a gene that’s usually on might be turned off; gene that’s usually off might be turned on

4. condensed or decondensed, affects gene expression

1. what is this loop a result of? 

1. paracentric inversion 

1. what happens when crossing over occurs after paracentric inversion in heterozygotes?

1. half the gametes are nonviable, and no recombinant progeny are observed

2. creates a dicentric and acentric chromatid

1. what is a dicentric chromatid? 

1. abnormal chromosome structure that contains two centromeres instead of one

1. what is an acentric chromatid? 

1. abnormal chromosome structure that has no centromere

1. how does chromosome 4 differ between humans and chimpanzees? 

1. pericentric inversion on human chromosome

2. shown by G-banding patterns

1. what is the result of an acentric chromatid? AKA what happens when a chromosome has no centromere? 

1. the fragment cannot bind to microtubules during mitosis or meiosis

2. nonviable gametes

1. what is the result of a dicentric chromatid? 

1. nonviable gametes

1. what happens in heterozygotes when a pericentric inversion forms an inversion loop during prophase I? 

1. does NOT create a dicentric and an acentric chromatid

1. a dicentric chromosome is produced when crossing over takes place in an individual heterozygous for which type of chromosome arrangement? 

   1. duplication

   2. deletion

   3. paracentric inversion

   4. pericentric inversion

c. paracentric inversion

what are these conditions a result of?

1. Cri-du-chat syndrome

2. Wolf-Hirschhorn syndrome

3. Williams-Beuren syndrome

deletions