sex determination Flashcards
(18 cards)
What is the diploid number in humans?
46
How many pairs are there?
23
How many of these pairs are non-sex chromosomes?
22
What is a non-sex chromosome known as?
Autosomes
What are the sex chromosomes?
XX or XY
What is the probability of being male or female?
50%
What are the examples of sex-linked conditions?
Colour blindness, haemophilia
What is colour blindness caused by?
Recessive allele on the X chromosome
Which chromosome doesn’t carry this allele?
Y chromosome
Which chromosome is smaller?
Y chromosome
Where would the gene come from if the father didn’t have the recessive allele (and it was male)?
The mother
Who cannot pass sex linked traits onto their sons?
The fathers
Why do sex linked traits occur more often in males?
No allele on the Y chromosome so the X chromosome is always expressed
What is a useful way to show a trace or inheritance?
Pedigree charts
How can it be proven that an allele is recessive?
2 unaffected parents with an affected child
The parents must be heterozygous
How can it be proven if an allele is not sex linked (when the trait is recessive)?
2 unaffected parents who have an affected daughter
The father would pass on the dominant allele on the X chromosome so all daughters would be unaffected
How can it be proven if an allele is dominant?
2 affected parents who have unaffected children
Both parents must be heterozygous and pass on their recessive alleles
How can it be proven that an allele is not sex linked (when the trait is dominant)?
2 affected parents with an unaffected daughter
The father would pass on his dominant allele on his X chromosome so all daughters would be affected
