Sex Linkages Flashcards
most animals and plants exhibit?
sexual dimorphism: when different sexes (male and female) exhibit different characteristics.
in most cases, sex is determined by?
a special pair of chromosomes called the sex chromosomes.
what is the xy system in humans?
humans have 22 pairs of autosomes and 2 sex chromosomes.
females: 2 x chromosomes
males: xy chromosomes
females are called the __ sex?
homogametic sex
males are called the __ sex?
heterogametic sex
what is the sry gene?
the sex determining region y gene is a gene located on the y chromosome. this gene produces a protein that leads to the development of testes.
when do the gonads start to develop and into what? and depends on what?
the gonads start to develop at 2 months. they develop into ovaries or testes. this depends on the presence of the y chromosome.
what are sex linked?
sex linked are genes located on the sex chromosomes.
are the genes on the sex chromosomes related to sexual function?
no not necessarily
how many genes does the x chromosome have? what about y chromosome?
1100 genes, 78 genes
fruit flies and the xy system?
fruit flies have 3 pairs of autosomes and one pair of sex chromosomes.
females have xx
males have xy
what is fruit fly scientific name?
drosophila melanogaster
what are the advantages to using the fruit fly?
- readily available
- have 4 pairs of chromosomes
- short life cycle
- simple to cross
what was morgan able to show through his studies on the fruit fly?
he was able to show that the gene for eye color in fruit flies was located on the x chromosome. genes located on sex chromosomes are called sex linked.
morgan extended the work of mendel by describing ?
x linked inheritance
wild type eye color for the flies?
red eyes: the phenotype for a character that is normally found in the natural population.
what are mutant phenotypes?
alternates to the wild type
what was his experiment like?
- he crossed a red eyed female with a white eyed male. XNXN . XWY
- the F1 offspring were all red eyed. red is dominant to white.
- Then he allowed the F1 individuals to mate with eachother: self cross: leading to F2 generation.
- the offspring in the f2 generation exhibited a 3:1 ratio of red eyes to white eyes but there was an important difference.
ALL WHITE EYED OFFSPRING WERE MALES AND RED WERE BOTH MALES AND FEMALES.
what was the conclusion from his experiment?
the experiment showed that the gene for eye color was located on the x chromosome.
- this was significant discovery because it helped scientists understand that genes are carried on chromosomes and some traits are linked to the sex of the individual.
x linked recessive traits are more commonly expressed in males because they only need one copy of the recessive allele to show the trait.
