Chapter 11 Flashcards
Why do linked genes not show independent assortment?
Because two recombinant gametes can result from crossing over between the homologous chromosomes when paired in prophase I
What’s the difference between parental and recombinant phenotypes?
Parental are the ones that inherit the chromosomes that were not involved in recombination in the dihybrid parent
Recombinant can only occur from crossing over
What is the minimum to maximum recombinant frequency possibilities?
1% to 50%
How do you find the frequency percentage of the recombinants?
Divide the number of recombinants by the total progeny and multiply that by 100
What is the unit of a linkage map?
Map unit (mu)
Also called the centimorgan (cM)
It is equal to the frequency percentage
what type of cross is used to see if two genes are linked or not?
Test cross
What is a linkage map?
A map of a chromosome that shows the distance (map units) two or more genes on the same chromosome are apart
What are sex-linked genes?
Genes located on the sex chromosomes (one or more pairs per person)
What are autosomes?
Any other chromosome other than sex chromosomes
Why is the sex determining gene on the Y chromosome?
The SRY gene
Master switch that directed development toward maleness at an early point in embryonic development
When does the SRY gene become active in sex determination in the embryo?
After 6-8 weeks
What is a wild type allele and what’s it’s notation?
A normal genotype where any change from wild type is a mutant
Add a subscripted + to the allele to show its a wild type
Can be recessive or dominant alleles
What is a pedigree chart?
How are males and females represented?
A chart that shows all parents and offspring for as many generations as possible
Includes sex and trait of interest
Males- square
Females- circle
What is a Barr body?
The inactive, condensed X chromosome in the nucleus as a dense mass of chromatin
How do you determine if a given gene is sex linked or not?
If it is sex linked you will get difference ratios since the male can only carry one allele on its X chromosome
What are the four major forms of chromosome alterations after breakages?
- Deletion occurs if a corker segment is lost
- Duplication occurs if a broken segment is inserted into the homologous chromosome
- Translocation occurs if a broken segment is attached to a different chromosome
- Inversion occurs if a broken segment is reattached to the same place but in reverse
What is nondisjunction or misdivision?
What do these result in?
Nondis- The failure of homologous pairs to separate during the first meiotic division
Mis- the failure of chromatids to separate during the second meiotic division
Results in a loss or gain of whole chromosomes (aneuploids)
Aneuploids vs euploids vs polyploids?
Aneuploids- individual with extra or missing chromosomes
Euploids- normal sets of chromosomes
Polyploids- individuals that receive one or more extra copies of the entire haploid complement of chromosomes
How does Down syndrome occur?
Nondisjunction or misdivision of chromosome 21
How are polyploids formed?
Failure of spindle to function normally during mitosis
Fails to separate duplicated chromosomes
What is autosomal recessive inheritance?
A pattern in which individuals who are homozygous for the dominant allele are free of symptoms and are not carriers while those homozygous recessive show the trait
What is autosomal dominant inheritance?
The allele that causes he trait is dominant
(Most often cases)
Homozygous recessive people are unaffected
What is X-linked recessive inheritance?
Traits due to inheritance of recessive alleles carried on the X chromosome
What is genetic counselling?
Allows prospective parent to assess the possibility that they might have an affected Child.
It begins with identification of parental genotypes through pedigrees and works it’s way down
What is prenatal diagnosis?
Where cells derived from a developing embryo or its surrounding tissues are tested for the presence of mutant alleles or chromosomal alterations
What is amniocentesis?
Cells are obtained from the amniotic fluid (water surrounding embryo in mothers uterus) to test for genetic faults
What is chorionic villus sampling?
Cells are obtained from portions of the placenta that develop from tissues of the embryo to test for genetic faults
How are inherited disorders detected before symptoms arise?
Genetic screening
What is cytoplasmic inheritance?
The pattern of inheritance follows that of genes in the cytoplasmic organelles (mitochondria and chloroplasts)
Do you have more of your fathers DNA or mothers? Why?
Mothers since the mitochondria’s DNA is all from your mother
What is genomic imprinting?
The expression of an allele of a particular nuclear gene is based on whether an individual organism inherits the allele from the male or female parent
What is the phenomenon “loss of printing”?
Where the imprinting mechanism for a gene does not work