Sex linkage Flashcards
how many chromosomes do humans have ?
-46 which are organised in 23 pairs
what is the term given to the non sex chromosomes?
-autosomes
how many pairs of sex chromosomes do humans have?
-one
what are the sex chromosomes of a female and a male?
-female XX
-male XY
how many sex chromosomes will enter a gamete?
-only one from each parent
what chromosome will females give gametes? what will males?
-all females give the X
-males will give 50% an X and another 50% a Y
what are the 3 common diseases that occur in males on sex linkage chromosomes? what type of sex linked allele causes these?
-green- red colour blindness
-haemophilia
-muscular dystrophy
-caused by single recessive allele on the X chromosome
If most sex linked conditions are causes by a recessive allele on the X chromosome, why are females unlikely to have it?
-females can be carriers of the disease
-the likely do carry the recessive X chromosome however the effects of this are masked by the dominant allele on their other X chromosome
-this causes them to be carriers of the disease but are not personally effected by it
why are males more likely to suffer from sex linked diseases caused by the recessive allele on X?
-they only have one X chromosome and they do not carry this gene on their Y chromosome to mask the effects of this allele which results in the disease
for a male child to inherit a sex linked disease what must his mother be?
-a carrier for the disease and it does not matter what the fathers alleles for this disease are
how can females inherit a sex linked condition, even through it is very rare?
-their father would have to have the condition e.g. have the recessive allele on his X chromosome
-their mother would have to be a carrier
what do pedigree charts show?
-the inheritance of a condition through several generations
what are the shapes used in a pedigree chart and what do they represent?
-males are squares
-females are circles
-shading of the shapes indicate that the individual has the condition
what are the 4 ways that conditions can be inherited?
-autosomal recessive
-autosomal dominant
-X linked recessive
-X linked dominant
how is autosomal recessive inheritance shown in a pedigree chart?
-only shown in some generations
-mostly even numbers of male and female will be effected
-carried on non sex chromosomes
how it autosomal dominant inheritance shown in a pedigree chart?
-condition is passed on with at least one parent having the trait
-effects even numbers of female and males
how is X linked recessive inheritance shown in a pedigree chart?
-more common in males than females
-a carrier mother will pass the condition onto half of her sons
how is X linked dominant inheritance shown in a pedigree chart?
-not restricted to just males
-a father with the condition will pass on the trait to his daughters
what kind of genes are used in a monohybrid inheritance cross?
-genes with at least 2 alternative forms of an allele
what is the main cause of having more than 2 different forms of an allele? is these alleles recessive or dominant usually?
-due to mutation
-usually they are recessive
what are 2 conditions that are inherited through autosomal recessive inheritance?
-cystic fibrosis
-albinism
what is the main condition inherited by autosomal dominant inheritance?
-Huntington’s disease
