Chapter 5.8 Modes of Inheritance ✓ Flashcards
What are the four main modes of single-gene inheritance?
-Autosomal dominant
-Autosomal recessive
-X-linked dominant
-X-linked recessive
Define autosomal inheritance
The passing on of a trait through a gene located on an autosome, a chromosome that is not a sex chromosome
Define carrier
In reference to a genetic disease, a carrier is a healthy, heterozygous organism carrying an allele for a recessive phenotype.
Define X-linked
Related to a gene located on the X chromosome
What pair of sex chromosomes do females have?
XX
What pairs of sex chromosomes do males have?
XY
Define sex-linked
Describes a gene located on a sex chromosome
Define X-linked recessive
When a phenotype is determined by a recessive allele on the X chromosome
Define Y-linked
Related to a gene located on the Y chromosome
Which gender is X-linked recessive traits more common in and why?
Males because they only have one X chromosome and will be affected regardless of whether the allele is dominant or recessive
Which gender is Y-linked traits more common in and why?
Males because they are the only sex to carry a Y chromosome
Describe and explain the occurrence of phenotypes that are X-linked recessive
-X-linked recessive traits are caused by recessive alleles on the X chromosome
-Males (XY): only one X chromosome. If it carries the allele, the trait is expressed (no second X to mask it.
-Females (XX): Must inherit two copies of the allele to express it the trait. One copy = carrier
Result:
-More common in males
-Can skip generations (passed by female carriers to sons)
-Examples; Haemophilia, red-green colour blindness
Describe and explain the occurrence of phenotypes that are Y-linked
-Y-linked traits are caused by genes located on the Y chromosome
-Males (XY): Only males have a Y chromosome so if it carries the allele, the trait is expressed
-Females (XX): Do not have a Y chromosome, so it cannot inherit or express Y-linked traits
Results
-Only males are affected
-Daughter are never affected
Describe and explain the occurrence of phenotypes that are X-linked dominant
-X-linked dominant traits are caused by dominant alleles on the X chromosome.
-Males (XY): Only one X chromosome so if it carries the allele, the trait is expressed
-Females (XX): Only one copy of the allele is needed for the trait to be expressed.
Result
-Both males and females can be affected
-Affected males pass the trait to all daughters but not sons
-Affected females have a 50% chance of passing the trait to each child, regardless of sex
