TH- Chromosomal basis of inheritance Flashcards
Describe Law of segragation
alleles for each gene separate during gamete formation, so each gamete formed will only have one allele from the gene
Describe Law of Independent Assortment
genes for different traits assort independently of each other during gamete formation
Which structure undergoes the segregation and assortment?
chromosomes
explain alleles vs genes
-genes are segments of DNA and each gene has 2 alleles
What are the 2 advantages of working with fruit flies?
- a single mating produces hundreds of offsprings so a new generation can be bred every 2 weeks
- they only have 4 chromosomes
What is wild type?
a phenotype for a character most commonly observed in the natural population
What are mutant phenotypes?
traits that are different from the wild type
what mutation did morgan observe after mating his flies for many months and how did he symbolize the alleles?
- white eyes
- w^+ = red eyes, w = white
which eye colour allele was dominant and which was ressesive for the fruit flies?
- red was dominant
- white reccessive
why did morgan conclude that eye colour was a sex-linked gene?
because only males had white eyes in the F1 generation
why did the white eyes show up in males whose mother was heterozygous and father had red eyes?
- the eye colour was on the X chromosome and males only have 1 X chromosome so one copy of the recessive w allele turned their eyes red
- whereas the females have 2 X chromosomes so they inherited the dominant and recessive genes causing them to have red eyes
If X and Y chromosomes are different how are they able to behave as homologs?
Y chromosone has short segment at either ends that are homologous to the X chromosome hence allowing them to pair up
what gene is required for the development of testes, where is it found and what happens if it is absent?
- SRY gene on Y chromosomes
- if absend then ovaries will form even with XY chromosomes
What is a sex-linked gene? and specific names when its on X and Y
- a gene located on the sex chromosomes
- X = X-linked genes
- Y = Y-linked genes
Why the amount of disorders that can be passed from a Y chromosome much less than X?
because there are only a few genes on the Y chromosome and most of them code for proteins that help in the functioning of the testes
What gene is required for the development of female gonads, where is it found and what happens if an embryo with XY has extra copies of the gene?
- the gene WNT4 makes a protein that promotes ovary development
- it is found on chromosome 1, an autosome
- if a XY embryo has extra copies of WNT4 it can develop female gonads
what is hemizygous?
an individual who has only one member of a chromosome pair or chromosome segment rather than the usual two.
If an X-linked trait is due to a recessive allele, a female will express the phenotype only if …? and why is that?
- only if she is homozygous for the allele
- because males are hemizygous
what does Duchenne muscular dystrophy do to the body, name of protein missing and which type of linked disorder is this?
- progressive weakening of the muscles and loss of coordination due to absence of a key muscle protein called dystrophin
- X-linked disorder
what does Hemophilia do to the body and which type of linked disorder is this?
- Hemophilia is caused by the absence of one or more of the proteins required for blood clotting.
- When a person with hemophilia is injured they clot much slower
- X-linked disorder
What is Barr body?
Inactive X in each cell of a female
Why do females not have twice the amount of proteins if they have 2 X chromosomes?
- due to the fact that 1 X chromosome is inactivated forming a Barr body during early embryonic
- development hence that X is not expressed
where is Barr body found?
lies along the inside of the nucleus envelope
where are Barr body chromosomes reactivated?
- in cells that make eggs
- so every gamete has an active X chromosome after meiosis
What is mosaicism and how does it affect female cells?
- being composed of cells of two genetically different types.
- some cells have an active X from the father and some from mother
explain how the X chromosome inactivated and mention the gene involved
- attachment of methyl groups (—CH3) to DNA nucleotides causing DNA methylation
- two regions, one on each X chromosome, associate briefly with each other in each cell
- one of the genes, called XIST (for X-inactive specific transcript), becomes active only on the chromosome that will become the Barr body
- Multiple copies of the RNA product of this gene attach to the X chromosome on which they are made eventually almost covering it.
- Interaction of this RNA with the chromosome initiates X inactivation
What are linked genes?
2 or more genes on the same chromosomes inherited together
What is genetic recombination?
production of offspring with combinations of traits that differ from those found in either P generation parent.
What are parental types?
offspring that inherits a phenotype that matches either of the parents
What is crossing over?
two homologous non-sister chromatids (1 maternal and 1 paternal) pair up with each other and exchange different segments of genetic material to form two recombinant chromosome sister chromatids.
What is a genetic map ?
-an ordered list of the genetic loci along a particular chromosome.
what is recombination frequency?
% of recombinant offsprings
what did Sturtevant predict about crossing over?
- the farther apart two genes are, the higher the probability that a crossover will occur between them
- hence higher the recombination frequency.
what is a linkage map?
a genetic map based on recombination frequencies
what are map units?
distances between the genes
What is nondisjunction and how does it affect amount of chromosomes in a gamete?
- it is when a pair of homologous chromosomes do not move apart properly during meiosis I or sister chromatids fail to separate during meiosis II
- out of 4 gametes 2 are normal but one gamete receives two of the same type of chromosome and another gamete receives no copy.
what is aneuploidy?
when a zygote has an abnormal number of chromosomes.
when is a aneuploid zygote is said to be monosomic? and provide n expression
when it has only 1 copy of chromosomes instead of the 2 found in diploid cells. (2n-1)
when is a aneuploid zygote is said to be trisomic? and provide n expression
when it has three copies of a chromosome instead of two. (2n+1)
What is polyploidy?
condition in which an organism has more than two complete sets of chromosomes
State the 2 types of polyploidy
Triploidy (3n) and Tetraploidy (4n), there are more…
How can a triploidy form?
fertilization of an abnormal diploid egg produced by nondisjunction of all its chromosomes.
How can a tetraploidy form?
Failure of a 2n zygote to divide after replicating its chromosomes, resulting later on in a 4n embryo.
What 4 types of changes can occur due to breakage of a chromosome?
- deletion
- duplication
- inversion
- translocation
What is deletion in terms of breakage of chromosome?
removes a chromosomal segment causing certain genes to be missing
What is duplication in terms of breakage of chromosome?
repeats a segment
What is inversion in terms of breakage of chromosome?
reverses a segment within a chromosome (changes orientation of the segment)
What is translocation in terms of breakage of chromosome?
moves a segment from one chromosome to another non homologous chromosome
Is down syndrome a polyploidy or aneuploidy condition?
aneuploidy
Why do people get down syndrome?
Because the cells are trisomic for chromosome 21
Why do Aneuploid conditions involving sex chromosomes appear to upset the genetic balance less than those involving autosomes?
- Y chromosome carries relatively few genes
- extra copies of the X chromosome become inactivated as Barr bodies.
Describe Klinefelter syndrome by saying what is different compared to normal and symptoms
- when a male has an extra X chromosome forming XXY
- have male sex organs, but the testes are abnormally small
- man is sterile
- even though extra X is inactivated there may be some breast enlargement and feminine characteristics
- may have subnormal intelligence
What happens to males born with an extra Y chromosome?
undergo normal sexual development and do not exhibit any well-defined syndrome, but tend to be taller than average.
What happens to females born with extra X chromosome?
- are healthy and have no unusual physical features other than being slightly taller than average.
- are at risk for learning disabilities
- are fertile.
Describe Turner syndrome by saying what is different compared to normal, symptoms and what is given to them that helps them form secondary sex characteristics?
- Monosomy X
- they are sterile because their sex organs do not mature.
- when provided with estrogen replacement therapy girls develop secondary sex characteristics
Describe cri du chat (“cry of the cat”) by saying what is different compared to normal and symptoms?
- due to deletion in chromosome 5
- severely intellectually disabled, has a small head with unusual facial features, and has a cry that sounds like the mewing of a distressed cat
- usually die early
Describe how chronic myelogenous leukemia (CML) develops and what it leads to
- translocation happens during mitosis of cells that are precursors of white blood cells
- Philadelphia chromosomes form due to exchange of a large portion of chromosome 22 with a small fragment from a tip of chromosome 9 produces a shortened, easily recognized chromosome 22,
- causes cancer by creating a new “fused” gene that leads to uncontrolled cell cycle progression.
what is genomic imprinting?
is when expression of certain genes depend on whether they were inherited from the male or female parent
what does genomic imprinting do to an allele?
either silencing an allele in one type of gamete (egg or sperm) or activating it in the other
How does genomic imprinting silence or activate alleles?
-imprint seems to consist of methyl (—CH3) groups that
are added to cytosine nucleotides of one of the alleles.
-Such methylation may silence the allele,
- However, for a few genes, methylation has been shown to activate expression of the allele.
What are cytoplasmic/ extranuclear genes?
genes located on organelles in the cytoplasm
who are extranuclear genes inherited from?
they are inherited maternally because the zygote’s cytoplasm comes from the egg
what do products of mitochondrial genes help make?
protein complexes of the electron transport chain and ATP synthase
what happens if there is a defect in one of these proteins made by mitochondrial genes?
-reduce the amount of ATP the cell can make and cause a number of human disorders
which parts of the body are more susceptible to energy deprivation?
muscles and nervous system.
State 2 mitochondrial diseases
mitochondrial myopathy and Leber’s hereditary optic neuropathy
what does Leber’s hereditary optic neuropathy cause?
produce sudden blindness in people
what does mitochondrial myopathy cause?
weakness, intolerance of exercise, and muscle deterioration.
Which parent is mitochondrial disorders inherited from and why?
mother because we receive our mitochondria from her
