Week 3 Flashcards
Pedigrees, Sex chromosomes, X-linked recessive traits, and allele variation
What are pedigrees?
A pictorial representation of a family history, outlining the inheritance of one or more characteristics
How are males represented in pedigrees?
A square
How are females represented in pedigrees?
A circle
How are unaffected individuals represented in pedigrees?
An empty/white symbol/shape
How are affected individuals represented in pedigrees?
A shaded in/coloured symbol/shape
How are obligate carriers represented in pedigrees?
A dot in the middle of the individual’s symbol/shape
How is consanguinity/inbreeding represented in pedigrees?
Two lines between individuals
How is birth order represented in pedigrees?
Children are listed from left to right in birth order
What is a carrier?
An individual who carries the allele for a trait, but does not demonstrate the phenotype/is unaffected (heterozygous)
What is the difference between autosomal traits and sex-linked traits?
- Autosomal: affect both sexes equally
- sex-linked: one sex is affected more than the other (depending on trait)
Which two types of traits tend to skip generations?
- Autosomal recessive
- X-linked recessive
T or F: Offspring affected by an autosomal recessive trait are usually born to affected parents.
False. Offspring affected by an autosomal recessive trait are usually born to unaffected parents.
When both parents are heterozygous for an autosomal recessive trait, how many offspring will be affected?
Approximately 1/4
What type of trait appears more frequently among children of consanguineous mating?
Autosomal recessive
Which three types of traits tend to not skip generations?
- Autosomal dominant
- X-linked dominant
- Y-linked
T or F: An offspring affected by an autosomal dominant trait must have at least one affected parent (unless they possess a new mutation).
True
When one parent is affected by an autosomal trait and the other is unaffected, how many offspring will be affected?
Approximately half
T or F: Unaffected parents can’t transmit autosomal dominant traits.
True
What type of trait affects both sexes, but tends to affect more males than females?
X-linked recessive
What type of trait is observed in a pedigree when affected sons are born to unaffected mothers?
X-linked recessive
What type of trait are all daughters carriers for if their father is affected?
X-linked recessive
In a cross between a mother who is heterozygous for an X-linked recessive trait and a father who is unaffected, what portion of their daughters are expected to be heterozygous carriers?
1/2
In a cross between a mother who is heterozygous for an X-linked recessive trait and a father who is unaffected, what portion of their sons are expected to be affected?
1/2
What type of trait is never passed from father to son?
X-linked recessive
Why are X-linked recessive traits always expressed in males?
Because they only have one X chromosome and the Y chromosome doesn’t carry an allele of that gene to “dominate” the recessive trait
What type of trait affects both sexes, but tends to affect more females than males?
X-linked dominant
What type of trait affects males only if their mothers are also affected?
X-linked dominant
T or F: Females affected by X-linked dominant traits must have an affected father or an affected mother.
True
Which type of trait affects all daughters of affected fathers?
X-linked dominant
A female heterozygous for an X-linked dominant trait will pass that trait to what portion of her sons and daughters
Half of the sons and half of the daughters will be affected
What type of trait only affects males?
Y-linked traits
How are Y-linked traits passed to offspring?
Passed from father to all sons
How many of the genes in the X chromosome have counterparts in the Y chromosome?
Almost none
Where do the X and Y chromosomes share homology?
A small region on the tips of their arms
T or F: Meiosis in a female results only in X-bearing eggs.
True
What is the ratio of X-bearing and Y-bearing sperm resulting from meiosis in a male?
1:1
