Week 3

Question 1

What are pedigrees?

Answer 1

A pictorial representation of a family history, outlining the inheritance of one or more characteristics

Question 2

How are males represented in pedigrees?

Answer 2

A square

Question 3

How are females represented in pedigrees?

Answer 3

A circle

Question 4

How are unaffected individuals represented in pedigrees?

Answer 4

An empty/white symbol/shape

Question 5

How are affected individuals represented in pedigrees?

Answer 5

A shaded in/coloured symbol/shape

Question 6

How are obligate carriers represented in pedigrees?

Answer 6

A dot in the middle of the individual’s symbol/shape

Question 7

How is consanguinity/inbreeding represented in pedigrees?

Answer 7

Two lines between individuals

Question 8

How is birth order represented in pedigrees?

Answer 8

Children are listed from left to right in birth order

Question 9

What is a carrier?

Answer 9

An individual who carries the allele for a trait, but does not demonstrate the phenotype/is unaffected (heterozygous)

Question 10

What is the difference between autosomal traits and sex-linked traits?

Answer 10

• Autosomal: affect both sexes equally
• sex-linked: one sex is affected more than the other (depending on trait)

Question 11

Which two types of traits tend to skip generations?

Answer 11

• Autosomal recessive
• X-linked recessive

Question 12

T or F: Offspring affected by an autosomal recessive trait are usually born to affected parents.

Answer 12

False. Offspring affected by an autosomal recessive trait are usually born to unaffected parents.

Question 13

When both parents are heterozygous for an autosomal recessive trait, how many offspring will be affected?

Answer 13

Approximately 1/4

Question 14

What type of trait appears more frequently among children of consanguineous mating?

Answer 14

Autosomal recessive

Question 15

Which three types of traits tend to not skip generations?

Answer 15

• Autosomal dominant
• X-linked dominant
• Y-linked

Question 16

T or F: An offspring affected by an autosomal dominant trait must have at least one affected parent (unless they possess a new mutation).

Answer 16

True

Question 17

When one parent is affected by an autosomal trait and the other is unaffected, how many offspring will be affected?

Answer 17

Approximately half

Question 18

T or F: Unaffected parents can’t transmit autosomal dominant traits.

Answer 18

True

Question 19

What type of trait affects both sexes, but tends to affect more males than females?

Answer 19

X-linked recessive

Question 20

What type of trait is observed in a pedigree when affected sons are born to unaffected mothers?

Answer 20

X-linked recessive

Question 21

What type of trait are all daughters carriers for if their father is affected?

Answer 21

X-linked recessive

Question 22

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?

Answer 22

1/2

Question 23

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?

Answer 23

1/2

Question 24

What type of trait is never passed from father to son?

Answer 24

X-linked recessive

Question 25

Why are X-linked recessive traits always expressed in males?

Answer 25

Because they only have one X chromosome and the Y chromosome doesn’t carry an allele of that gene to “dominate” the recessive trait

Question 26

What type of trait affects both sexes, but tends to affect more females than males?

Answer 26

X-linked dominant

Question 27

What type of trait affects males only if their mothers are also affected?

Answer 27

X-linked dominant

Question 28

T or F: Females affected by X-linked dominant traits must have an affected father or an affected mother.

Answer 28

True

Question 29

Which type of trait affects all daughters of affected fathers?

Answer 29

X-linked dominant

Question 30

A female heterozygous for an X-linked dominant trait will pass that trait to what portion of her sons and daughters

Answer 30

Half of the sons and half of the daughters will be affected

Question 31

What type of trait only affects males?

Answer 31

Y-linked traits

Question 32

How are Y-linked traits passed to offspring?

Answer 32

Passed from father to all sons

Question 33

How many of the genes in the X chromosome have counterparts in the Y chromosome?

Answer 33

Almost none

Question 34

Where do the X and Y chromosomes share homology?

Answer 34

A small region on the tips of their arms

Question 35

T or F: Meiosis in a female results only in X-bearing eggs.

Answer 35

True

Question 36

What is the ratio of X-bearing and Y-bearing sperm resulting from meiosis in a male?

Answer 36

1:1