Chapter 15 Flashcards
What is the chromosome theory of inheritance?
genes have specific loci/ positions along chromosomes, and it is the chromosomes that undergo segregation and independent assortment
What was Thomas Hunt Morgan’s experiment?
Used fruit flies to study genetics
Why did Morgan use fruit flies? (3)
They were prolific breeders
only four pairs of chromosomes that are all easily distinguishable
3 pairs of autosomes and one pair of sex chromosomes
WWhat are prolific breeders? (2)
Single mating results in hundreds of offspring
new generation arises quickly
What is a wild type and an example?
phenotype for a character most commonly observed in a natural population
example- red eyes in fruit flies
What are mutant phenotypes? (3)
traits alternative in the wild type
caused by alleles mutated from wild-type alleles
example- white eyes in fruit flies
How are gene notations used to symbolize alleles? (3)
Receives it from the first mutant discovered
a positive sign means it is the wild-type
example- red eyes in fruit flies are symbolized by w+
How did Morgan determine allele behavior? (4)
breed white-eyed male fly with red-eyed female fly
resulted in a F1 generation of all red-eyed flies
F2 generation resulted in a 3:1 Red:white
All the white eyes were males
Why were all the white-eyed fruit flies male? (4)
the recessive allele is only on the x chromosome
since males only have one X chromosome, no dominant allele can mask the recessive allele
Females can only have white eyes if it received two recessive alleles
this is impossible since F1 generation all had red eyes
How do Y chromosomes differ from X chromosomes?
they are much smaller
How do Y chromosomes link to X chromosomes?
Short segments at the end of the Y chromosomes are the only regions homologous with regions of the X chromosomes
How do sex chromosomes segregate in mammals? (3)
During mitosis
egg receives one x chromosome
half the sperm receives X and the other half receives Y
How do female offsprings develop?
During conception, a sperm cell with an X chromosome fertilizes an egg
How do male offsprings develop?
During conception, a sperm cell with a Y chromosome fertilizes an egg
How does the Y chromosome cause male gamete formation? (2)
In humans, the presence of Y chromosomes determines if the generic gonad in the beginning of development will develop into testes or ovaries
Gene SRY (sex determining region of Y) on the Y chromosome is required for testes development
X-0 System (4)
Exhibited by some insects
Possess only X chromosomes
Females have XX, males have only X
Sperm can contain either an X chromosome or no chromosome
Z-W system (3)
Exhibited in birds, fish, and insects
the sex chromosome present in the egg determines the sex
females have ZW, males are ZZ
Haplo-diploid system (3)
for animals without sex chromosomes like bees and ants
females develop from fertilized eggs and are diploid
males develop from unfertilized eggs and are haploid (no father)
Sex-linked genes
located on either sex chromosome
Y-linked genes (3)
genes located on Y chromosome
passed along intact from father to all sons
very few genes, thus few disorders are also passed along by Y-linked genes
X- linked chromosomes (2)
Genes located on X chromosomes
Since males and females have different numbers of X chromosomes, patterns of inheritance differ from those produced by genes on autosomes
Inheritance of X-linked genes (3)
Fathers can pass all their X-linked chromosomes but not to sons
Mothers pass x-linked chromosomes to both sexes
If X-linked traits are recessive,
females- express the phenotype only if she is homozygous
males- hemizygous
What does hemizygous mean? (3)
Possess only one X chromosome so it cannot be heterozygous or homozygous
If the recessive trait is received, they will express it
More likely to receive X-linked recessive disorder
