SEX-LINKED TRAITS AND SEX-LINKED PATTERNS OF INHERITANCE Flashcards
____of an individual is determined by the ____contributed to the zygote by the sperm and the egg
sex
sex chromosomes
• An egg can donate an
• A sperm can donate an
X
X or Y
Therefore the___ determines the sex of a child
sperm
In humans, sex is determined by the _____pair
23 rd chromosome
• Humans egg cells always have an ____ chromosome
• Human sperm cells have____chromosomes
X
either an X or a Y chromosome
• If a sperm with an X fertilizes the egg, the 23 rd pair will be____ and it will be a female
• If a sperm with a Y fertilizes the egg, the 23 rd pair will be ___and it will be a male
XX
XY
SEX-LINKED INHERITANCE
• Using____ as test subjects,____ studied eye colour using simple monohybrid crosses.
• Red eyes (R) are dominant over white eyes (r).
fruit flies
Thomas Morgan
SEX-LINKED INHERITANCE
• When he crossed purebred white-eyed males with red-eyed females, he was unable to produce a female with white eyes.
• He concluded that the gene must be located on the
X chromosome
SEX CHROMOSOMES CAN CARRY OTHER GENES TOO = _________________
SEX LINKED TRAITS
Traits carried on the sex chromosome (23rd pair in humans); most are carried on the X chromosome
Sex-linked traits
• Most known sex-linked traits are____
• This is probably because the___ chromosome is much larger than the___ chromosome.
X-linked (carried on the X chromosome)
X
Y
The inheritance of traits that are located on the _____depends on the sex of the parent carrying the trait.
sex chromosomes
•_____ show up in different % in males and females because they move with the sex chromosomes
•____ linked genes show up in males.
SEX LINKED TRAITS
Y
Sex-linked traits are inherited differently in men and women –
____have two X chromosomes, so they have 2 genes for all traits carried on the 23 rd pair
____have one X chromosome, so they only have 1 gene for all traits carried on the 23 rd pair
Females
Males
Whether or not recessive sex-linked traits get passed on depends on the sex of the parent and the sex of the offspring
• Males pass their X chromosome (and its genes) to all of…..
• Females pass one of their X chromosomes (and its genes) to all of…
their daughters and none of their sons
their children
Sex-linked Inheritance
- Sex-linked Dominant Inheritance
- Sex-linked Recessive Inheritance
• Refers to situations where a single dominant allele on the X chromosome can lead to a trait/condition
X – Linked Dominant Inheritance
Sex-linked Dominant Inheritance
- The trait does not skip generations.
- Affected males must come from affected_____.
- Approximately____ the children, both sons and daughters, of an affected heterozygous female are affected.
- Affected females come from affected…
- All the….., of an affected father are affected.
mothers
half
mothers or fathers.
daughters, but none of the sons
• Refers to those situations where a recessive allele on the X chromosome can lead to a trait/condition or disorder.
X – linked Recessive Inheritance
Sex-linked Recessive Inheritance
- Most affected individuals are__.
- All daughters of an affected male will be_____ and all sons will be____.
- Affected males result from _____ who are affected or who are known to be carriers because they have affected brothers, fathers or maternal uncles
- Affected females come from affected….
- All the sons of affected____ should be affected.
- Approximately half the sons of carrier____ should be affected.
male
carriers\ unaffected
Mothers
fathers and affected or carrier mothers
females
females
X – linked Recessive Inheritance
• Males are affected more often than females. Ratio of…
• Affected____ will transmit the allele to all daughters, but not to sons.
• Homozygous recessive____ can arise only from matings in which the father is affected and the mother is affected or a carrier
8:1
males
females
Genes carried on Y chromosome
Y-LINKED GENES
