Year 11 Human Biology - Sex Determination and Sex Linked Traits

which pair are the sex chromosomes

23rd pair

how do the x and y chromosome differ

size (x is larger)

genes carried

what is the genotypes for females and male

female - XX XO

male - Xy

is it even chance of being male and female

statistically equal numbers of male and female are born but this does not mean there is an equal distribution of gender within families

why does the father determine the sex

becaus eovum only have x chromosomes but a sperm can have an x chromosome or a y chromosome

what is sex linkage

the control of certain traits by genes located on the sex chromosome

mainly on the x chromosome

explain why sex traits are expressed differently in men and women

in women, they require the faulty gene for a sex linked trait to be on both of their x chromosomes for it to appear in the phenotype

however because men have and x and a y chromosome, with the y chromosome not having many corressponding alleles, they only require the allele on the x chromosome for it to be expressed

what is a carrier

a female who has the faulty gene on one chromosome but a domiant allele on the other x chromosome masks it

why are males hemizygotes in sex linkage

because they only carry 1 allele in the genotype

describe red green colour blindness

when you cannot distinguish between the 2 colours

describe duchenne muscular dystrophy

progressive wasting/atrophy of the muscles

first signs in age 3-5 when child cannot stand up without pushing off ground

death occurs when wasting reaches respiratory muscles

describe haemophilia

inability or reduced ability to clot blood due to lack of clotting factors

haemophila A lacks factor VIII

haemophilia B lacks factor IX