CH 13 Flashcards
Carl Correns
(1900)
first suggests central role for chromosomes
authored one of the scientific papers announcing rediscovery of Mendel’s worl
Walter Sutton
(1902)
Chromosomal theory of inheritance
based on observations that similar chromosomes paired with one another during meiosis
T.H. Morgan
(1910)
-Working with fruit fly, Drosophila melanogaster
-discovered a mutant male fly with white eyes instead of red
-crossed the mutant male to a normal red-eyed female
-all F1 progeny red eyed= dominant trait
When morgan crossed F1 females with F1 males, what happened in the F2 generation?
Contained red and white eyed flies, but all white eyed flies were male
Testcross of a F1 female with a white-eyed male showed what?
The viability of white eyed females
What did morgan conclude?
eye color gene resides on the female X chromosome
sex linked
traits determined by sex chromosome
sex chromosomes
a pair of dissimilar chromosomes that still pair during meiosis and mitosis
What is sex determination in Drosophila based on?
The number of X chromosomes
XX (Humans)
female
XY (humans)
male
ZW (birds)
female
ZZ (birds)
male
XX (grasshoppers)
female
XO (grasshoppers)
male
diploid (honeybees)
female
haploid (honeybees)
male
Humans have a total of __ chromosomes
___ are automosomes
___ pair of sex chromosomes
46; 22; 1
__ chromosomes is highly condensed
Y
recessive alleles on male’s X have no active _____ on Y
counterpart
“default” for humans is ____
female
In organisms with XY determination, are a lot of genes from the Y chromosome expressed?
No, few are
Why can a single recessive sex linked gene produce recessive phenotype?
Recessive alleles on X chromosome have no active partner on Y
certain genetic diseases affect males to a ____ degree than females
greater
X linked recessive alleles:
red green color blindless
hemophilia
dosage compensation
ensures equal expression of genes from sex chromosomes even through number of chromosomes is different between sexes
In mammalian female cells, 1 X chromosome is randomly inactivated and is highly condensed into a _____ _____
barr body
females heterozygous for genes on the X chromosome are ____ ______
genetic mosaics
(Chromosome theory exceptions)
Mitochondria and chloroplasts contain _____
genes
(Chromosome theory exceptions)
Traits controlled by these genes do not follow the ____
Chromosomal theory of inheritance
(Chromosome theory exceptions)
Genes from mitochondria and chloroplasts are often passed to the offspring by only one parent, often the _____, called _____ inheritance
mother; maternal
(Chromosome theory exceptions)
In plants, chloroplasts are also often inherited from the mother, although this is species _____
dependent
(Genetic Mapping)
Early geneticists realized that they could obtain information about the ______ between genes on a chromosome
distance
(Genetic Mapping)
Distance estimates based on ….
patterns of genetic recombination (crossing over) between genes
(Genetic Mapping)
If crossover occurs, parental alleles are…
recombined, producing recombinant gametes
The Creighton and McClintock experiment Hypothesis
Crossing over involves a physical exchange of genetic material
The Creighton and McClintock experiment Prediction
Recombination of visible differences in a chromosome should correlate with genetic recombination of alleles
The Creighton and McClintock Experiment Test
-
-
yellow extension; green knob, kernel color, kernel texture
The Creighton and McClintock experiment Results
Genetically recombinant progeny also have physically recombinant chromosomes
The Creighton and McClintock experiment conclusion
A physical exchange of genetic material accompanied genetic recombination
What did Alfred Sturtevant do?
Undergraduate in TH Morgan’s lab and put morgan’s observation that recombinant progeny reflected relevant location of genes in quantitative terms
(Alfred Sturtevant)
As physical distance on a chromosome increases…
so does the probability of recombination (crossover) occurring between the gene loci
recombination frequency
recombinant progeny/ total progeny
If homologues undergo two crossovers between loci…
then the parental combination is restored
Multiple crossovers lead to an ____ of the true genetic distance
underestimate
Odd numbers of crossover events produce…
recombinant gametes
No crossover or even numbers of crossovers produce…
parental gametes
Is the relationship between true distance on a chromosome and the recombination frequency linear?
No
Crossing over
genetic recombination between non sister chromatids
crossing over allows the homologues to exchange….
Chromosomal material
in crossing over, alleles of genes that were formerly on separate homologues can now…
be found on the same homologue
chiasmata
site of crossing over
(three point testcross)
uses ___ loci instead of 2 to construct maps
3
(three point testcross)
middle gene allows …
tracking of recombination events on either side
(three point testcross)
in any three point cross, the class offspring with two crossovers is…
the least frequent class
(three point testcross)
in practice, geneticists use three point crosses to determine …
the order of genes, then use data from the closes two point crosses to determine distances
some genetic disorders affect males more than females, that is ____ ____
sex linked
Hemophilia
a disease that affects a single protein in a cascade involved in formation of blood clots
For of hemophilia is caused by an …
heterozygous females are ____ ____
X linked recessive allele; asymptomatic carriers
Human genetic disorder causes
A single amino acid change in a single protein can result in clinical syndrome
Sickle cell anemia
first human disease shown to be the result of a mutation in a protein
what is sickle cell anemia caused by?
a defect in the oxygen carrier molecule, hemoglobin
leads to impaired oxygen delivery to tissues
Homozygotes for sickle cell allele exhibit ….
intermittent illness and reduced life span
Heterozygotes in sickle cell anemia appear….
normal, do have hemoglobin with reduced ability
Why is sickle cell allele is particularly prevalent in people of African descent
Proportion of heterozygotes higher than expected
confers resistance to blood borne parasite that causes malaria, explains higher proportion of allele
Nondisjunction
the failure of homologues or sister chromatids to separate properly during meiosis
aneuploidy
gain or loss of a chromosome, the result of nondisjunction
monosomy
loss
trisomy
gain
Which autosomes are severe defects and can die within a few months?
13, 15,18
Which autosomes can survive to adulthood?
21 and 22
Down syndrome
trisomy 21
Do nondisjunction of sex chromosomes generally experience severe developmental abnormalities?
No
In nondisjunction of sex chromosomes, individuals have somewhat ______ _______ but often reach maturity and in some cases, may be fertile
abnormal features
XXX
triple X females
XXY
males (Klinefelter syndrome)
XO
females (Turner syndrome)
OY
nonviable zygotes
XYY
males (Jacob syndrome)
