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BIO Exam I - Stack 3

The chromosomal basis of inheritance

QuestionAnswer
Mendelian inheritance has its physical basis in the ___ of chromosomes. behavior
___ genes exhibit unique patterns of inheritance. Sex-linked
Alterations in chromosome ___ or ___ cause some genetic disorders. - number - structure
genes segments of DNA located along chromosomes
the chromosome theory of inheritance - a basic principle in biology stating that genes are located at specific positions (loci) on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns - AS CHROMOSOMES GO, SO DO THE GENES
The arrangement of chromosomes at metaphase I of meiosis and their movement during anaphase I account for the ___ and ___ of the alleles for different characters. - the segregation - independent assortment
The first evidence associating a specific ___ with a specific ___ came from the work of Thomas H. Morgan. - gene - chromosome
Why did Morgan choose the fruitfly as his experimental organism? - a single mating produces many offspring - new generations can be bred often - they have only 4 pairs of chromosomes, which can be easily seen with a light microscope
After some two years of breeding work, what did Morgan discover amongst the fruit flies he was examining? a mutation (suddenly, a male fruit fly had white eyes instead of red)
wild type the phenotype for a character most commonly observed in natural populations (such as red eyes in fruit flies)
mutant phenotype - traits that are alternatives to the wild type (such as white eyes in fruit flies) - they are due to alleles assumed to have originated as changes, or mutations, in the wild-type allele
Explain where the designations w+ and w came from. - the letter is based off of the mutant phenotype (w = white eyes) - the + identifies the allele for the wild type trait (w+ = red eyes)
What happened when Morgan crossed a white-eyed male with a wild-type (red-eyed) female? - the F1 generation all had red eyes - so, red eyes are the dominant trait
What happened when Morgan crossed an F1 red-eyed female with a F1 red-eyed male? - the F2 generation shown a typical Mendelian ratio of 3 red-eyed flies to 1 white-eyed fly - however, no females displayed the white-eye trait; all white-eyed flies were males - mutant trait sex-linked to X chromosome!
A chromosome in a diploid organism is hemizygous when ___. - only one copy is present - (for example, male fruit flies are hemizygous for the eye color gene; it's only on the X chromosome)
How did Morgan's work provide support for the chromosome theory of inheritance? - his finding of the correlation between a particular trait and an individual’s sex / a specific gene is carried on a specific chrom. (eye-color gene on the X-chrom.) - also indicated that genes located on a sex chrom. exhibit unique inheritance patterns
What did Morgan's work show about inheritance patterns when genes are located on a sex chromosome? - the phenotypes are not equally distributed on male and female offspring - fathers pass X-linked alleles to all of their daughters but to none of their sons - mothers can pass X-linked alleles to both sons and daughters
Describe the chromosomal basis of sex in humans. - there are 2 kinds of sex chromosomes: X and Y - the Y-chromosome is much smaller than the X - the sex of the organism depends on whether the sperm cell contains an X- or Y-chromosome
Describe the chromosomal basis of sex in grasshoppers, cockroaches, and some other insects. - only one type of sex chromosome: the X - females are XX, males are X - sex determined by whether the sperm cell contains an X-chromosome or nothing
Describe the chromosomal basis of sex in birds, some fishes and some insects? - the sex chromosomes present on the egg determine the sex of the offspring - females are ZW, males are ZZ - (the opposite of humans)
Describe the chromosomal basis of sex in most bees and ants? - there are no sex chromosomes - females develop from fertilized eggs (diploid) - males develop from unfertilized eggs (haploid); have no father
What is on the Y chromosome that has to do with the development of testes? - the Y-chromosome has a gene on it that is required for the development of testes: SRY (sex-determining region of Y) - in the absence of SRY, the gonads develop into ovaries
sex-linked genes genes located on either sex chromosome
linked genes genes located close enough together on a chromosome that they tend to be inherited together
What is so different about the inheritance of Y-linked and X-linked genes? - X-linked genes can be present in both males and females - Y-linked genes can only be present in males
If a color-blind woman married a man who had normal color vision, what would be the probable phenotypes of their children? - so, X^n X^n x X^N Y - 50% chance to have a child with color blindness, 50% chance to have a carrier - all male children will be colorblind, all females carriers
What is Duchenne muscular dystrophy and how does it work? - a human genetic disease characterized by progressive weakening and a loss of muscle tissue - caused by a sex-linked recessive allele
What is hemophilia and how does it work? - a human genetic disease characterized by excessive bleeding following injury - caused by a sex-linked recessive allele resulting in the absence of one or more blood-clotting proteins
The cells of female and male mammals have the same effective dose (one copy) of most X-linked genes. How does this happen if females have two X chromosomes and males have only one X chromosome? - most of one X-chromosome in each cell in female mammals becomes inactivated during early embryonic development
Barr body - a dense object lying along the inside of the nuclear envelope in cells of female mammals, representing a highly condensed, inactivated X-chromosome - become reactivated during gamete formation
When does X inactivation in female mammals occur and what does that mean? - one X inactivated during early embryonic development - its random which X-chrom. will be inactivated in the embryonic cells present at that time - so, females consist of a mosaic of 2 types of cells (active X from father or active X from mother)
What’s the deal with X inactivation in tortoiseshell cats? - you can clearly see the resulting mosaic from X inactivation - female cats will have random patches of black and orange fur
What is nondisjunction and how does it result in abnormal chromosome numbers? - an error in meiosis in which the members of a pair of homologs do not move apart properly during meiosis I or sister chromatids fail to separate during meiosis II - so, some gametes might have one less or one more chromosome than they should
What happens in meiosis I nondisjunction? What is the result? - homologous chromosomes fail to separate during anaphase I - the end result is 2 gametes with an extra chromosome (n+1) and 2 with one less (n-1)
What happens in meiosis II nondisjunction? What is the result? - sister chromatids fail to separate during anaphase II - the end result is 2 normal gametes (n), 1 with an extra chromosome (n+1), and 1 with one less (n-1)
aneuploidy a chromosomal aberration (deviation from the norm) in which one or more chromosomes are present in extra copies OR are deficient in a number
What would you get if a n+1 sex cell united with an n sex cell? - aneuploidy (one extra chromosome) - zygote would be trisomic (2n+1)
What would you get if a n-1 sex cell united with an n sex cell? - aneuploidy (one less chromosome) - zygote would be monosomic (2n-1)
What is polyploidy? How does it happen? - a chromosomal alteration in which the organism possesses more than two complete chromosome sets - it is the result of an accident of cell division
How do you get a triploid? - chromosomal sets of 3...3n - may arise by the fertilization of an abnormal diploid egg produced by nondisjunction of all its chromosomes
How do you get a tetraploid? - chrom. sets of 4...4n - could result from the failure of a 2n zygote to divide after replicating its chrom.s; subsequent normal mitotic divisions would then produce a 4n embryo - fertile; has pairs of chrom.s, so meiosis can occur (allodiploids cant)
What is an alloploid? - a hybrid individual or cell with two or more sets of chromosomes derived from two different ancestral species - can be allodiploid, allotriploid, etc.
What is Down syndrome? - aneuploid condition (2n+1); 47 chromosomes instead of 46 - extra #21 chromosome (trisomy 21)
What is Klinefelter syndrome? - aneuploid condition (2n+1); 47 chromosomes instead of 46 - extra X-chromosome in a male (XXY)
What is Jacob's syndrome? - aneuploid condition (2n+1); 47 chromosomes instead of 46 - extra Y-chromosome (XYY)
What is trisomy X? - aneuploid condition (2n+1); 47 chromosomes instead of 46 - extra X-chromosome in a female (XXX)
What is Turner syndrome? - aneuploid condition (2n-1); 45 chromosomes instead of 46 - only one X-chromosome
What is cri du chat? - disorder caused by altered chromosome - deletion in chromosome #5
What is chronic myelogenous leukemia? - disorder caused by altered chromosome - reciprocal translocation between chromosome #9 and #22 - shortened chromosome #22 is then called the Philadelphia chromosome
Created by: jessica.gvc