9.20-9.23: Sex Chromosomes and Sex-Linked Genes Flashcards
(12 cards)
The Y chromosome, that determines maleness, has a gene called SRY. What does SRY stand for? What does this gene do? If the gene is not present, what happens?
Sex-determining region of Y; codes more male reproductive anatomy; ovaries will develop.
Humans have one way of determining sex. How do some insects determine sex?
Using the X-O system. XX creates female offspring, while animals lacking in a sex chromosome are male.
What is one alternative sex-determining system found in some fishes, butterflies and birds?
ZZ male, ZW female. Sex determined by whether egg is Z or W.
How are the sex of ants determined?
By number of chromosomes; there are no sex chromosomes. Females develop from fertilized (diploid) egg, while males are haploid; fatherless.
Can environment affect the sex of a organism?
Yes! Certain temperature during reptilian embryonic development can help determine the sex of the baby.
End of 9.20 Question: King Henry VIII of England was quick to blame his wives for bearing him only daughters. Explain how, from a genetic point of view, his thinking was wrong.
The male sperm determines the sex of the baby, in the human X-Y system.
Do sex chromosomes contain genes unrelated to sex? If so, what are these genes called?
Yes; sex-linked gene.
What differentiates patterns of inheritance in sex-linked genes to autosomes?
Certain traits can be passed down only to certain sexes. Consider this: X chromosomes are bigger than Y chromosomes. They have space for genes that Y chromosomes do not. Therefore, sex linked genes are written as X^RX^R for females but X^RY for males. This “R” can be an “r” as well. However, this gets tricky because on the possible R types for the three Xs involved in sexual reproduction, certain genders could only get certain traits. See pg. 176 for diagrams.
Why do sex-linked disorders affect more males than females?
because, if a man inherits only one X-linked recessive alleles, from his mother— the allele will be expressed. In contrast, a woman has to inherit two such alleles–one from each parent– to exhibit the trait. we also know, from earlier, that most sex-linked disorders are recessive.
What are some common sex-linked disorders?
Hemophilia (excessive bleeding) and Duchenne muscular dystrophy.
End of 9.22 Question: Neither Tom nor Sue has hemophilia, but their firstborn child does, if the couple has a second child, what is the probability that they will also have the disease?
1/4 (1/2 chance of a male child * 1/2 chance that he will inherit the mutant X).
End of 9.23 Question: Why is the Y chromosome particularly useful in tracing recent human heritage? Who were a couple of the guys that were traced back to?
Because it is passed directly from father to son (barring mutations) forming an unbroken chain of male lineage. Genghis Kahn and Niall of the Nine Hostages.
