Genetics Chapter 4
How does inheritance work in humans?
A female inherits X-linked alleles from both parents; a male inherits X-linked alleles from his female parent only.
Hemophilia is an Xx-linked recessive disease in humans. A woman with hemophilia mates with a man who exhibits normal blood clotting. What s the probability that their child will have hemophilia?
All of the males will have hemophilia and none of the females will have it. 1/2
What did sex chromosomes evolve from?
Autosomes
How are sex-linked characteristic determined?
By genes on the sex chromosomes. X-linked characteristics are encoded by genes on the X chromosome, and Y-linked characteristics are encoded by genes on the Y chromosome.
A geneticist discovers a male mouse with greatly enlarged testes in his laboratory colony. He suspects that this trait results from a new mutation that is either Y linked or autosomal dominant. How could he determine whether the trait is autosomal dominant or Y linked?
Cross the mouse with a normal female. Take that mouse and cross the females with normal mice. If any of the male offspring exhibit enlarged testes, then it is autosomal dominant and not Y linked.
What is the evolution of the Y chromosome?
Crossing over between the X and the Y chromosomes has been suppressed, by palindromic sequences within the Y chromosome allow for internal recombination on the Y chromosome. This internal recombination sometimes leads to chromosome rearrangements that can adversely affect sexual development.
How do the sex chromosomes differ in males and females?
Differ in number and appearance. The homogametic sex produces gametes that are all identical with regard to sex chromosomes; the heterogeametic sex produces gametes that differ in their sex-chromosome-composition.
What unusual feature of the Y chromosome allows some recombination among the genes found on it?
Eight large palindromes allow crossing over within the Y chromosome
Where are Y-linked characteristics found?
Found only in males and are passed from a father to all of his sons.
How does the heterogametic sex differ from the homogametic sex?
Gametes of the heterogametic sex have different sex chromosomes; gametes of the homogametic sex all have the same sex chromosome.
How do chromosomal, genic, and environmental sex-determining systems differ?
In chromosomal sex determination--males and females have chromosomes that are distinguishable. In genic sex determination, sex is determined by genes, but the chromosomes of males and females are indistinguishable. In environmental sex determination, sex is determined fully or in part by environmental effects
What is genic sex determination?
In which genotypes at one or more loci determine the sex of an individual organism. Others have environmental sex determination.
What is the phenotype of a person who has XXXY sex chromosomes?
Klinefelter syndrome
What is sex determination?
Mechanism by which sex is specified is termed sex determination. Sex may be determined by differences in specific chromosomes, genotypes, or environment.
What process causes the genetic variation seen in offspring produced by sexual reproduction?
Meiosis
What happens to the X chromosomes in placental mammals?
One of the two X chromosomes in females is normally inactivated. Which X chromosome is inactivated is random and varies from cell to cell. Some X-linked genes escape X inactivation, and other X-linked genes may be inactivated in some females but not in others. X inactivation is controlled by the Xist gene.
How can sex be predicted in Drosophila melanogaster?
Predicted by the X: A ratio determined by genes on the X chromosome.
How is sex ultimately determined in humans?
Presence or absence of the SRY gene located on the Y chromosome
What is sexual reproduction?
Production of offspring that are genetically distinct from their parents. Most organisms have 2 sexual phenotypes- male and female.
What is the ZZ-ZW system?
Sex determination, Males possess two Z chromosomes, whereas females possess a Z chromosome and a W chromosome.
What is the XX-XY system?
Sex determination, females possess two X chromosomes, whereas males posses a single X chromosome and a single Y chromosome.
What is the XX-XO system?
Sex determination, females possess two X chromosomes, whereas males possess a single X chromosome.
Red green color blindness in humans is due to an X linked recessive gene. Both John and Cathy have normal color vision. Cathy gave birth to a color blind daughter. John filled for divorce, claiming he is not the father of the child. Is John justified in his claim of nonpaternity? If Cathy had given birth is a color blind son, would John be justified in claiming nonpaternity?
Since color blindness is a recessive trait, the color blind daughter must be homozygous recessive. Because the color blindness is X linked, then John has grounds for suspicion. Normally, their daughter would have inherited John's X chromosome. Because John is not color blind, he could not have transmitted a color blind X chromosome to his daughter. A remote alternative possibility is that the daughter is XO, having inherited a recessive color blind allele from her mother and no sex chromosome from her father. In that case, the daughter would have Turner syndrome. If Cathy had a color blind son, then John would have no grounds for suspicion. The son would have inherited John's Y chromosome and the color blind X chromosome from Cathy
What kind of gametes do males create? Females?
Small. Large.
How many Barr bodies does a male with XXXYY chromosomes have in each of his cells?
Two Barr bodies.
What was the genotype of the few F1 red-eyed males obtained by Bridges when he crossed a white-eyed female with a red-eyed male?
X+Y
Joe has classic hemophilia, an X-linked recessive disease. Could Joe have inherited the gene for this disease from the following persons? Why or why not? a. His mother's mother b. His mother's father c.His father's mother d.His father's father
X-linked recessive diseases have to be able to skip generations. a. Yes. The grandmother could needs to be heterozygous, and the father could be either affected or not affected. if his mother was heterozygous and the father was dominant, it would be possible for Joe to have inherited the trait. b.Yes ^^^^ c. X-linked recessive diseases have to be able to skip generations. If his father's mother had this disease, his father would inherit it 100% (since males have one X chromosome). We could not classify this case as x-linked recessive. d.X-linked recessive diseases have to be able to skip generations. If his father's father had this disease, it would be silenced by the mother's genes and he would not be the reasoning for this. We could not classify this case as x-linked recessive.
What is the sexual phenotype of the fruit flies having the following chromosomes? Sex Chromosomes: Autosomal Chromosomes: a. XX All normal b. XY All normal c. XO All normal d. XXY All normal e. XYY All normal f. XXYY All normal g. XXX All normal h. XX Four haploid sets i. XXX Four haploid sets j. XXX Three haploid sets k. X Three haploid sets l. XY Three haploid sets m.XX Three haploid sets
a. Female b. Male c. MALE (Why? This cannot be a female because it needs two Xs. This is a sterile male.) d. FEMALE (WHY? Two X chromosomes) e.Male (Why? Only one X chromosome) f. Male (has extra chromosomes) g. Metafemale (why? Triploids with three X chromosomes are always female ) h. Female i. Metafemale (Why? Triploid) j. Metafemale (Why? Triploid) k. Sterile Female l.Male m.Female
how many barr bodies would you expect to see in human cells containing the following chromosomes?
a. XX-1 barr body b.XY-0 c.XO-0 d. XXY-1 e. XXYY-1 f. XXXY-2 g. XYY-0 h. XXX-2 i. XXXX-3 human cells inactivate all X chromosomes beyond one. The Y chromosome has no effect on X inactivation
red green color blindness in humans is due to an X linked recessive gene. A woman whose father is color blind possesses one eye with normal color vision and one eye with color blindness a.propose an explanation for this woman's vision pattern b. would it be possible for a man to have one eye with normal color vision and one eye with color blindness?
a. the woman is heterozygous, with one X chromosome bearing the allele for normal vision and one X chromosome with the allele for color blindness. one of the two X chromosomes is inactivated at random during early embryogenesis. If one eye derived exclusively from cells that inactivated the normal X, then that eye would be color blind, whereas the other eye may e derived from progenitor cells that inactivated the color blind X b. one way would be for the man to be XXY and the answer to part a would abbly.
In organisms with the ZZ-ZW sex determining system, from which of the following possibilities can a female inherit her Z chromosome
her mother's mother-NO her mother's father-NO her father's mother-YES her father's father-YES females inherit the W chromosome from the mother and the Z chromosome from the father. If we exclude the possibility that the mother and father are sibilings of the same paternal line, then no Z chromosome can be inherited from the mother's parents. Males inherit one copy of the Z chromosome from each parent, so females have equal probability of inheriting the Z chromosome from the father's mother or the father's father