sex chromosomes Flashcards
1
Q
sex chromosomes
A
- 22/23 chromosomes are similarly shaped (autosomes)
- 23rd pair are sex chromosomes (gonosomes)
- longer is x, two in female one in male (homogametic)
- shorter is y, one in male (heterogametic)
2
Q
sex determination
A
- xx chromosomes gonad tissue will develop into ovary and foetus will grow into female
- xy chromosome gonad tissue will develop into testis and foetus into male
- sex determine by presence of y chromsome
- switch occurs 7-8 week of development
- in mammals, xy is male
- birds and butterflies, xy is female
- special type of monohybrid inheritance
3
Q
sex linked alleles
A
- y chromosome short, few alleles other than those responsible for ‘maleness’
- x chromosome long, many alleles also addition of ‘femaleness’
- very small part of x and y can pair (complimentary genes) no crossing occurs
- alleles carried on non-homologous part of x chromosome (x-linked genes / sex-linked alleles)
4
Q
how are sex-linked alleles inherited?
A
- men have 1 x chromosome, one of each sex-linked alleles
- women have 2 x chromosomes, inherited by either sex, male can only receive only one of the possible alleles
- female can be either homozygous or heterozygous
