Chapter 15 Flashcards
What is the chromosome theory of inheritance?
genes have specific loci/ positions along chromosomes, and it is the chromosomes that undergo segregation and independent assortment
What was Thomas Hunt Morgan’s experiment?
Used fruit flies to study genetics
Why did Morgan use fruit flies? (3)
They were prolific breeders
only four pairs of chromosomes that are all easily distinguishable
3 pairs of autosomes and one pair of sex chromosomes
WWhat are prolific breeders? (2)
Single mating results in hundreds of offspring
new generation arises quickly
What is a wild type and an example?
phenotype for a character most commonly observed in a natural population
example- red eyes in fruit flies
What are mutant phenotypes? (3)
traits alternative in the wild type
caused by alleles mutated from wild-type alleles
example- white eyes in fruit flies
How are gene notations used to symbolize alleles? (3)
Receives it from the first mutant discovered
a positive sign means it is the wild-type
example- red eyes in fruit flies are symbolized by w+
How did Morgan determine allele behavior? (4)
breed white-eyed male fly with red-eyed female fly
resulted in a F1 generation of all red-eyed flies
F2 generation resulted in a 3:1 Red:white
All the white eyes were males
Why were all the white-eyed fruit flies male? (4)
the recessive allele is only on the x chromosome
since males only have one X chromosome, no dominant allele can mask the recessive allele
Females can only have white eyes if it received two recessive alleles
this is impossible since F1 generation all had red eyes
How do Y chromosomes differ from X chromosomes?
they are much smaller
How do Y chromosomes link to X chromosomes?
Short segments at the end of the Y chromosomes are the only regions homologous with regions of the X chromosomes
How do sex chromosomes segregate in mammals? (3)
During mitosis
egg receives one x chromosome
half the sperm receives X and the other half receives Y
How do female offsprings develop?
During conception, a sperm cell with an X chromosome fertilizes an egg
How do male offsprings develop?
During conception, a sperm cell with a Y chromosome fertilizes an egg
How does the Y chromosome cause male gamete formation? (2)
In humans, the presence of Y chromosomes determines if the generic gonad in the beginning of development will develop into testes or ovaries
Gene SRY (sex determining region of Y) on the Y chromosome is required for testes development
X-0 System (4)
Exhibited by some insects
Possess only X chromosomes
Females have XX, males have only X
Sperm can contain either an X chromosome or no chromosome
Z-W system (3)
Exhibited in birds, fish, and insects
the sex chromosome present in the egg determines the sex
females have ZW, males are ZZ
Haplo-diploid system (3)
for animals without sex chromosomes like bees and ants
females develop from fertilized eggs and are diploid
males develop from unfertilized eggs and are haploid (no father)
Sex-linked genes
located on either sex chromosome
Y-linked genes (3)
genes located on Y chromosome
passed along intact from father to all sons
very few genes, thus few disorders are also passed along by Y-linked genes
X- linked chromosomes (2)
Genes located on X chromosomes
Since males and females have different numbers of X chromosomes, patterns of inheritance differ from those produced by genes on autosomes
Inheritance of X-linked genes (3)
Fathers can pass all their X-linked chromosomes but not to sons
Mothers pass x-linked chromosomes to both sexes
If X-linked traits are recessive,
females- express the phenotype only if she is homozygous
males- hemizygous
What does hemizygous mean? (3)
Possess only one X chromosome so it cannot be heterozygous or homozygous
If the recessive trait is received, they will express it
More likely to receive X-linked recessive disorder
What is Duchenne muscular dystrophy? (2)
progressive weakening of the muscle and loss of coordination
Absence of a muscle protein specific on the X chromosome
What is X inactivation? (8)
Occurs in female mammals
one of the x chromosome becomes inactive
regions of X chromosomes contain genes for inactivation
XIST (X inactivate specific transcript) activates in the barr body X chromosome
random and independent from other cell
results in a mosaic of cells that have active X chromosome from the father or mother
all mitotic descendants have the same inactive X
Prevents double of proteins that are encoded on X chromosome
What is a Barr body? (3)
Condensed form of inactive X in each female cell
Found in the inside of the nuclear envelope
only expressed in the ovaries for meiosis
What are linked genes? (2)
Genes located near each other on the same chromosome
tends to get inherited together in genetic crosses
How are linked genes and inheritance correlated?
Some genes are inherited together, such as body color and wing size in fruit flies
What is genetic recombination?
production of offspring with combinations of traits that differ from those found in each P generation parent
What are parental types?
offsprings that have phenotypes that match the P generation
What are recombinant types?
offsprings with new combinations of traits differing from the P generation
What does a 50% frequency of recombination mean?
The two genes are located on different chromosomes and cannot be linked
How does the recombination of linked genes occur?
Crossing over breaks the physical connection between specific alleles of genes on the same chromosome
How does crossing over lead to recombinant alleles?
Meiosis distribute chromosomes in multitudes of combination
What is a genetic map?
ordered list of the genetic loci along a particular chromosomes
How does distance between genes affect recombination?
The farther apart two genes are, the higher the probability that a crossover will over between them and a higher recombination frequency
What is a linkage map?
A genetic map based on recombination frequencies
What is nondisjunction? (3)
members of a pair of homologous chromosomes do not move apart properly during meiosis 1 or sister chromatids fail to separate during meiosis 2
Results in One gamete receives two of the same chromosomes and another receives none
or
Aneuploidy- when a zygote has an abnormal number of a particular chromosome
What does monosomic mean?
aneuploid zygote with a missing chromosome
What does trisomic mean?
aneuploid zygote with additional chromosomes
What does polyploidy mean?
organisms with more than two complete chromosome sets in all somatic cells
What does triploidy mean? (2)
3n
Arises from a fertilized egg arising from a nondisjunction
What does tetraploidy mean? (2)
4n
Arises from a zygote failing to divide after replicating its chromosomes
What is chromosome deletion? (2)
when a chromosomal fragment is lost
Affected chromosome is missing certain genes
What is chromosome duplication?
when a deleted fragment attaches as an extra segment to a sister chromatid
What is inversion?
deleted fragment attaching to the original chromosome in reverse orientation
What is chromosome translocation?
deleted fragment to join a nonhomologous chromosome
Why is a syndrome?
characteristics of aneuploidy
What is down syndrome? (3)
aneuploid condition with an extra chromosome 21
Total of 47 chromosome
Aka trisomy 21
What is Klinefelter syndrome?
Males with an extra X chromosome
What is Trisomy X?
(XXX) females with three X chromosome
What is Monosomy X? (2)
turner syndrome
females with only one X chromosome
What is cri du chat? (2)
deletion in human chromosomes
Deletion in chromosome 5
What is chronic myelogenous leukemia caused by?
chromosomal translocation during mitosis of white blood cells
What is genomic imprinting? (4)
Traits in mammals that depend on which parent passes along the alleles for those traits
occurs during gamete formation
results in the silencing of a particular allele
imprints differently in sperm and egg
What is an example of genomic imprinting? (2)
Insulin growth factor 2 (Igf2)
only paternal allele is expressed
Where else can genes be found in eukaryotes?
Outside the nucleus
aka extranuclear genes
can be found in mitochondria
What can defective mitochondrial genes do?
affect ATP production
cause mitochondrial myopathy (weakness, muscle deterioration, intolerance of exercise)
cause Leber’s hereditary optic neuropathy (sudden blindness)
