Heredity Study Guide ANSWER KEY

Define the following terms.◦ Autosomes: Chromosomes 1-22 that hold genetic

information for self◦ Sex chromosomes: chromosomes X & Y that code for sex

of individual◦ Sex-linked trait: genes that are only in the X or Y

chromosomes ◦ Sex influenced trait: traits that are influenced by

hormones in the body◦ Pedigree: diagram that shows how a trait in inherited

over generations◦ Mutation: a change in a sequence of a gene, can be

beneficial or harmful◦ Nondisjunction: type of disorder when a chromosome

fails to split during meiosis and sex cells a different in number

What are some examples of linked genes?◦ Some examples of linked genes would be hair

and eye color, hair color and freckles, and pea color and pod shape.

What can you learn from a chromosome map?◦ A chromosomal map can determine where a

gene is including which chromosomes a disorder is found on.

What is a karyotype used for? How many chromosomes are in a normal karyotype?◦ A karyotype is used to determine the sex of an

individual and whether or not there is a chromosomal disorder. There are 46 chromosomes in a normal karyotype.

Be able to read and analyze a pedigree.

◦ What symbol represents female? circles◦ What symbol represents male? squares◦ What does it mean if a symbol is colored in? the person

will exhibit that trait and express it◦ What do horizontal lines between symbols represent? A

marriage or if there were offspring between the couple◦ How many children do parents 5 & 6 have? 3 children, 2

girls and 1 boy

Sex: male Chromosomal disorder? no If yes, which chromosome?

Sex: female Chromosomal disorder? no If yes, which chromosome?

Sex: female Chromosomal disorder? yes If yes, which chromosome? 1 X (Turner’s syndrome)

Sex: female Chromosomal disorder? yes If yes, which chromosome? 3 #21 (Down’s syndrome)

Sex: female Chromosomal disorder? yes If yes, which chromosome? 3 #13 (Patau syndrome)

Sex: female Chromosomal disorder? yes If yes, which chromosome? 3 #18 (Edward’s syndrome)

Explain why males determine the sex of their offspring in humans.◦ Males can create sperm cells that can offer either an X or Y

chromosome. ◦ Females can only offer an X chromosome. ◦ Depending on whether an X or Y sperm cell fertilizes an egg cell will

determine if the child is a boy or girl. ◦ If XX then it will be a girl. If XY then it will be a boy.

Use the karyotype above to answer the following question. The individual above is a suspect in a crime and new evidence shows that from DNA analysis the killer is a carrier for an X-linked disorder known as Duchenne muscular dystrophy. Could this individual possibly be a carrier for Duchenne muscular dystrophy? Name the genetic disorder that is individual has that could allow a male to be a carrier for an X-linked trait and whether they would be considered innocent of the crime.

◦ Yes, it is possible for this person to be a carrier for Duchenne muscular dystrophy because they have 2 X chromosomes and therefore can be a carrier if one is affected. This person has Klinefelter’s syndrome, which is XXY syndrome. They are males but have an extra X chromosome.

In humans, colorblindness is a recessive, sex-linked trait. What is the probability that the children of a woman heterozygous for colorblindness and a man with normal color vision will be colorblind? Explain your answer. ◦ The probability that the child of a woman that is

heterozygous for colorblindness and a man with normal vision is 25%. This child will be a male. There is a 25% chance they will have a female that is a carrier.

X XC

X XX XXC

Y XY XCY