Sex-linked Diseases & Polygenic Inheritance Flashcards
1
Q
What are some examples of sex-linked diseases?
A
- cleft palate
- diabetes insipidus
- red-green colour blindness
- haemophilia
- muscular dystrophy
2
Q
Why do certain genetic diseases seem to occur more often in males than in females?
A
- because the male has only 1 X chromosome
- so if a gene mutates or if a gene for a disease is present on this X chromosome, the male will get the genetic disease
- if the gene is recessive, it will only be expressed in the female if both X chromosomes have the allele
3
Q
What are examples of diseases caused by a recessive sex-linked allele on the X-chromosome?
A
- red-green colour-blindness
- haemophilia
4
Q
What is the main characteristic of polygenic inheritance?
A
- there is more than one pair of alleles responsible for a single trait
5
Q
How are the complex traits found in polygenic inheritance determined?
A
- they are determined by the interaction of many different alleles
- each having small individual effects on the offspring
- resulting in a range of phenotypes
6
Q
What is continuous variation?
A
- graduations of a characteristic in a phenotype
- e.g. height in humans
7
Q
How does continuous variation work?
A
- the more pairs of alleles that control a characteristic, the greater the number of possible combinations and the greater the variety of phenotypes
- each phenotype differs slightly from the next, forming a graduated series
8
Q
What are some examples of continuous variation in polygenic inheritance?
A
- height
- skin colour
- metabolic rate
- longevity
