Pedigrees and Sex-linked Traits (lesson eight)

Question 1

Inheritance of Traits

Answer 1

• scientists can track and analyze inheritance of traits
• For example, if a child displays a recessive phenotype, we know both parents must have heterozygous genotype for that trait and would be called “carriers”

Question 2

Pedigree Charts

Answer 2

• The simplest way to visually follow the inheritance of a gene is to construct a special type of family tree, called a pedigree
• This is a chart that traces the inheritance of a certain trait among members of a family

Question 3

a square

Answer 3

is a male

Question 4

a shaded square

Answer 4

is an affected male

Question 5

normal circle

Answer 5

is a female

Question 6

shaded circle

Answer 6

is an affected female

Question 7

a triangle connecting two siblings with a line in the middle

Answer 7

means the two siblings are identical twins

Question 8

a triangle connecting two siblings with a line on top of it

Answer 8

means the two siblings are fraternal twins

Question 9

How pedigree Charts are organised

Answer 9

• Each generation in identified by a Roman numeral
• Each individual within the generation is given a Arabic numeral where 1 is always the oldest child
• Oldest to youngest children are drawn from left to right

Question 10

Genetic Counsellors

Answer 10

• Genetic counsellors construct and analyze pedigrees to help trace the genotypes and phenotypes of a family
• This can be used to determine if and how any particular trait runs in a family

Question 11

Plant and Animal Breeders

Answer 11

• Pedigrees are also often used by plant and animal breeders
• These charts can be used to track both desirable and undesirable traits
• example, if you have a racehorse from a long line of prize-winning horses, you may charge another farmer a higher “stud fee” because the offspring produced are more likely to have those desirable traits

Question 12

Autosomal Inheritance

Answer 12

• If an allele is inherited on an autosome we say that it’s under the control of autosomal inheritance
• This type of inheritance affects both sexes equally and is not affected by the inheritance of sex chromosomes
• This is not always the case though

Question 13

Sex Linked Traits

Answer 13

• If an allele is on one of the sex chromosomes, the gender of the individuals will affect the inheritance of this trait
• This is because females are XX and males are XY

Question 14

X Linked

Answer 14

• If a genetic disorder is carried on the X chromosome we would say this is X-linked
• If the disorder is recessive, even if a male only inherits one copy of the gene he will express the disorder because he is XY
• A father also cannot pass on an X–linked trait to his sons, only his daughters

Question 15

examples of x-linked

Answer 15

• For example, red-green colour-blindness, hemophilia, and male-pattern baldness are all X-linked traits

Question 16

Y-Linked

Answer 16

• Y-linked disorders do exist but can only be passed from father to son
• One reason there are fewer is because the Y chromosome is much smaller and carries less genetic information than the X chromosome
• Sometimes, Y-linked disorders may cause reduced fertility in males and may require medical intervention