Chapter 13 Flashcards
Sex-linked (X-linked)
trait determined by a gene on X chromosome
What species did Thomas Morgan Hunt look into?
Drosophilia
Autosomes
any eukaryotic chromosomes not a sex chromosomes
What is the default sex in embryonic development?
Female
Genes on Y chromosome
Make male genitalia
Make secondary sexual structures
Any individual with one Y chromosome is normally
Male
Name an example of a human genetic disorder that is sex-linked?
Hemophilia
Which statement is true about inheritance of hemophilia between females and males
Heterozygous females are asymptomatic carriers
Men who receive a recessive allele on their X c’some have the disease
Barr body
Inactivated X chromosome
Dosage compensation
A phenomenon by which expression of genes carried on sex chromosomes is kept the same in males and females, despite a different number of sex chromosomes
Genetic mosaics
When a woman is heterozygous for a sex linked gene, some cells will express the dominant allele and other may express the recessive
Nondisjunction
failure of homologues to separate properly during meiosis
What are the possible aneuploidies when nondisjunction occurs in female meiosis?
XX or no X chromosomes (O)
What are the possible aneuploidies when nondisjunction occurs in male meiosis?
XY, YY, or no sex chromosomes (O)
Aneuploidy
gain or loss of a chromosomes
T or F: nondisjunction only occurs in sex chromosomes
F: nondisjunction occurs in both autosomes and sex chromosomes
Aneuploidy is a result of _________
Nondisjunction
Monosomy
loss of one copy of an autosome
Trisomy
gain of an extra autosome
Down syndrome
an extra copy (trisomy) on chromosome 21
T or F: Aneuploidy is more severe in sex chromosomes than in autosomes
F: It is LESS severe than in autosomes
Triple X (XXX)
develop as normal females with 2 Barr bodies
1/1000 females
Klinefelter syndrome (XXY)
develop as a male with many female characteristics, often mentally delayed
1/1000 male births
Turner syndrome (XO)
sterile female, stunted sexual development
1/5000 female births
Which aneuploidy variation is lethal during embryonic development?
YO
Generally what is the Chromosomal theory of inheritance? And how did Morgan’s early work find support for it?
Chromosomal theory of inheritance - theory stating hereditary traits are carried on chromosomes
Morgan found
How is sex determined in humans?
Sex chromosomes
Females: XX
Males: XY
How many autosomes do humans have? How many sex chromosomes?
Autosomes - 22 pairs
Sex chromosomes - 23rd pair
Which chromosomes determines ‘maleness’ in humans?
Y
If females have double the X-genes, do they express twice as many proteins encode on the X c’somes? Why or why not.
No, because of dosage compensation, which
True or false: Early in embryonic development in females, one X-chromosome gets turned off (Barr body) all cells in the adult female have the same X-chromosome inactivated.
True
Why do genetic mosaics form?
Nondisjunction of chromosomes in meiosis leads to ___________. (one word)
Aneuploidy
Down syndrome is an example of what type of chromosomal disorder?
Trisomy
Why would Aneuploidy in sex chromosomes is less severe than in autosomes?
Autosomes is densely packed with genes
E.g., if you lose chromosome 1, you will lose a lot of important genes
If you are missing a sex chromosome, more flexibility
Sex chromosomes have fewer genes essential for functioning
What you lost from a sex chromosomes is not as impairing as what you lost from an autosome
What types of disorders can result from Aneuploidy of sex chromosomes?
Triple X (XXX)
Klinefelter syndrome (XXY)
XO
OY
XYY (Jacob syndrome)
