Name: ___________________________
Period: _________
Date: ________________
Ms. Hartnett
Chapter 5, Lessons 4 & 5
HUMAN INHERITANCE
What are the Functions of the Sex Chromosomes?
 Body cells of humans have 23 chromosome pairs, or 46
chromosomes
 The sex chromosomes are the 23rd pair of chromosomes
 Sex chromosomes carry genes that determine a person’s sex
as being either male or female
 Sometimes, other genes are on these chromosomes too
Girl or Boy?
 Sex chromosomes are the only pair that don’t always match
 Girls have two sex chromosomes that do match
 These are called X chromosomes
 Boys have two chromosomes that don’t match
 They have an X chromosome and a Y chromosome
 The Y is much smaller than the X
Sex Chromosomes and Fertilization
 All egg cells carry one X chromosome
 Sperm cells can carry either an X or a Y
 If the sperm that fertilizes the egg has an X chromosome, the egg will then have
two X chromosomes
 Egg will develop into a girl
 If the sperm that fertilizes the egg has a Y chromosome, the egg will have an X
and a Y
 Egg will develop into a boy
Sex-Linked Genes
 Some genes are carried on sex chromosomes
 Sex-linked genes = alleles are passed from parent to child on sex
chromosomes
 Remember: the Y chromosome is much smaller than the X
chromosome
 This means they will have different genes
 Sex-linked genes also have dominant and recessive alleles
 A dominant allele on an X chromosome will hide a recessive allele on the other
X chromosome
 But for males, there isn’t a matching allele on the Y chromosome to hide the X
chromosome allele
 Any allele on the X chromosome will produce a trait in a male who
inherits it
Inheritance of Colorblindness
 Colorblindness = a trait controlled by a recessive allele on X chromosome
 Many more males than females have red-green colorblindness
 This is because females can carry the recessive trait and not express it
 Carrier = person who has one recessive allele and one dominant allele
 The carrier can pass on the recessive trait
ADVANCES IN GENETICS
How Can Organisms Be Produced with Desirable Traits?
 Everyone’s DNA is different
 DNA can show us how families are related and how we can make organisms
with desirable traits
 Three methods for developing organisms:
1. Selective breeding
2. Cloning
3. Genetic engineering
1. Selective Breeding
 Selective breeding = process of selecting organisms with desired traits to be
parents of the next generation
 Anyone have cows, goats, or farms?
 Which traits do you choose?
 Two ways to selectively breed:
1. Inbreeding
2. Hybridization
Inbreeding
 Inbreeding = crossing two individuals that have similar desirable
characteristics
 Crossing two golden retrievers that are both friendly and have the same
coloring
 This produces organisms that are very similar
 This type of selective breeding also increases the chance of getting two
recessive alleles
 Can lead to genetic disorders like cancer
Hybridization
 Hybridization = breeders cross two genetically different individuals
 Hybrid organism that results is likely to have the best traits from both
parents
 A farmer might cross corn that produces many kernels with corn that is
resistant to disease
 The farmer is hoping to get corn that produces many kernels and is
resistant to disease
2. Cloning
 Clone = organism that has exactly the same genes as the organism it came from
 Bacteria and plants are much easier to clone than animals
 For plants: cut the stem from one plant, put it in soil, soon you’ll have a
brand new plant that is identical to the first one
3. Genetic Engineering
 Genetic engineering = genes from one organism are transferred into the DNA
of another organism
 This can produce medicines and improve food crops
Genetic Engineering
in Bacteria
 Some bacteria can be genetically engineered to produce a human protein called
insulin
 This is for people with diabetes and need insulin shots
 Scientists just insert the gene for insulin into the DNA of the bacteria and the
bacteria will start making insulin
Gene Therapy
 Someday we might be able to use genetic engineering to correct genetic
disorders in humans
 Gene therapy = inserting copies of a gene directly into a person’s cells