Chapter 12 Flashcards
Mendel’s “hereditary factors” were genes which are?
segments of DNA located along chromosomes.
Chromosome theory of inheritance
-Mendelian genes have specific loci on chromosomes
-chromosomes undergo segregation and independent assortment
What evidence did Thomas Hunt Morgan find?
a specific gene is with a specific chromosome
Why is Drosophila Melanagaster a convenient organism for genetic studies? (4)
-produce many offspring
-new generation every 2 weeks
-have only 4 pairs of chromosomes
-traits are readily visible
Wild-type
common phenotype
Mutant phenotypes
uncommon phenotype
What was the first mutant phenotypes Thomas Hunt Morgan discovered?
fly with white eyes instead of red
When Morgan mated white eye males and red eyed females, the F2 generation?
had only males with white eyes
Morgan concluded that?
eye color was related to the sex of the fly
The white eyed mutant allele must be on the _____ chromosome
X
Morgan’s findings supported?
Chromosome theory of inheritance
Where are there regions that are homologous with corresponding regions on the X Chromosome?
Ends of the Y chromosome
Sex-linked gene
gene located on either sex chromosome
X-linked genes
genes on the X chromosome
Because of the complexity of the process of sex determination, ____.
many variations exist
Many _____ help determine sex
Y-linked genes
X chromosomes have genes for?
characters unrelated to sex
What needs to happen in order for a recessive X-linked trait to be expressed?
-female needs 2 copies of the allele (homosygous)
-male needs only one copy of the allele (hemizygous)
X-linked recessive disorders are more common in?
males
Disorders caused by recessive alleles on X chromosome:
-color blindness
-duchenne muscular dystorphy
-hemophilia
In females, the inactive x condenses into a?
barr body
If a female is __ for a particular gene located on the ___ chromosome, she will be?
heterozygous, X, a mosaic for that character
Each X chromosome has?
hundreds of thousands of genes
Linked genes
genes located on the same chromosome that tend to be inherited together.
Morgans experiment showed how linkage affects?
inheritance of 2 characters
Morgan crossed flies that differed in?
body color and wing size
Morgan find that body color and wing size are usually?
inherited together in specific combinations
Genetic recombination
production of offsrping with combinations of traits differing from either parent.
Genetic findings of Mendel and Morgan relate to?
Chromosomal basis of recombination
Mendel observed that combinations of traits in some offspring?
differ from either parent
parental types
offspring with a phenotype matching one of the parental phenotypes
recombinant types
offspring with nonparental phenotypes
50% frequency of recombination is observed for any?
2 genes on different chromosomes
Morgan proposed that some process must occasionally break the?
physical connection between genes on the same chromosome
recombinant chromosomes bring alleles together in?
new combinations in gametes
The abundance of genetic variation is what ___ works upon?
natural selection
genetic map
ordered list of the genetic loci along a particular chromosome
The farther apart 2 genes are?
the higher the crossover probability and recombinant frequency
linkage map
genetic map of a chromosome based on recombinant frequency.
genes that are far apart on the same chromosome have a recombination frequency near?
50%
Genes that are far apart on the same chromosome are physically connected but?
genetically unlinked
cytogenetic maps
indicate the positions of genes with respect to chromosomal features.
large-scale chromosomal alterations often lead to?
spontaneous abortions or developmental disorders
Nondisjuction
pair of homologous chromosomes do not separate normally during meiosis or sister chromatids do not separate during meiosis 2.
A result of nondisjunction is that one gamete receives?
two of the same type of chromosome and another receives none
Aneuploidy
results from fertilization of gametes in which nondisjunction occurs
monosomic zygote
has only one copy of a particular chromosome
trisomic zygote
has 3 copies of a particular chromosome
polyploidy
condition in which an organism has more than 2 complete sets of chromosomes
Polyploid is common in?
plants
deletation
removes a chromosomal segment
duplication
repeats a segment
inversion
reverses orientation of a segment within a chromosome
Translocation
moves a segment from one chromosome to another
A diploid embryo that is ___ for a large deletation is likely missing __ which is generally ___.
homozygous, a number of essential genes, lethal
Alterations of chromosome __ and ___ are associated with some serious disorders.
number, structure
Surviving individuals of alternation of chromosomes have?
a syndrome, characteristic of the type of aneuploidy
down syndrome
aneuploid conditions that results from 3 copies of chromosome 21
The frequency of down syndrome increases with?
age of the mother
Klinefelter syndrome is the result of?
an extra chromosome in the male, producing XXY
About ___ is born with an extra Y chromosome and ___.
1/1000 males, does not exhibit any defined syndrome
Females with ___ have ____ except ___.
Trisomy X (XXX) no unusual physical features, being taller than average
Monosomy X is also called
Turner syndrome
Monosomy X produces?
X0 females who are sterile
cri du chat
results from specific deletion in chromosomes
chronic myelogenous leukemia is caused by?
translocation of chromosomes
