Transcript Heredity Study Guide

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 is inherited over
generations
◦ Karyotype: a picture of chromosomes that can show the
sex and chromosomal disorders of an individual
◦ 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.
X
X
X
XX
XX
Y
XY
XY
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