Download Chapter 7 Notes Heterozygous (Bb) – the alleles given are both

Chapter 7 Notes
Heterozygous (Bb) – the alleles given are both dominant and recessive
Homozygous dominant (BB) – the alleles given are both dominant
Homozygous recessive (bb) – the alleles given are both recessive
Genotype – genetic makeup
Phenotype – physical characteristics
Monohybrid cross – one trait
Dihybrid cross – two traits
Autosomes or autosomal chromosomes or body cells – chromosome
sets 1-22
Gametes or Sex cells or sperm and egg – chromosome set 23
Section 1
2 copies of each gene is given to the offspring in sexual reproduction
Many human genetic disorders are caused by autosomal genes. These
can be predicted by using a Punnett square
Disorders caused by recessive alleles
 2 copies of the recessive allele must be present for a person to
have this disorder.
 This disorder will most often appear in offspring of parents who
are both heterozygotes.
 By being heterozytes, the parent is carrying a normal allele that
masks the disease causing recessive allele
 They are said to be carriers – not showing the disorder but can
pass it down
o Ex. Cystic fibrosis is a severe recessive disorder that mainly
affects the sweat glands and the mucus glands
Disorders caused by dominant alleles
 Far less common than recessive disorders
o Ex. Huntington’s disease a nervous system disorder that
develops later in life
Disorders caused by sex linked traits
 These are disorders that are linked either to the X or Y
chromosome.
XX – female
XY – male
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Female can only give an X chromosome to the offspring
Male can give either an X or a Y to the offspring
Y chromosome only has the trait to determine the male gender
X chromosome has many traits
o Ex. Colorblindness and sickle cell anemia
SECTION 2
Polygenic trait – poly means many genic means genes
 When several genes influence a trait
 The genes for this may be on the same chromosome or scattered
 Ex skin color, eye color, height, weight, hair color
Incomplete dominance – an individual displays a trait that is
intermediate between 2 parents
 This is a heterozygous phenotype that is somewhere between the
2 homozygous phenotypes
 Neither allele is completely dominant or recessive
 1 trait is shown
 Ex. Red flower reproduces with a white flower and you get a pink
flower
Codominance – when 2 dominant alleles are expressed at the same
time
 Both of the genes give are shown but neither allele is dominant or
recessive
 Ex. Red flowers reproduce with a white flower and you get a
white flower with red spots or stripes
Sometimes phenotypes are decided by the environment instead of the
sum of gene expression
 Ex. Turtles lay eggs in the sand. If the temperature is warmer the
turtles will become females and if it is cooler they will become
males
 Ex twins aren’t always identical
SECTION 4
Pedigree – a chart that can help trace phenotypes and genotypes in a
family.
 A family history that shows how a trait is inherited over several
generations
 Like a family tree that shows genetic disease
 Pedigree tells us where a genetic disorder is found
o Autosomal or sex linked (located on the x)
o Dominant or recessive
o Heterozygous or homozygous
Pedigree rules
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Circle = female
Square = male
Vertical lines = offspring
Read left to right for order of birth
Horizontal line = mating
Shading indicates disorder
o Trait with whole color means it came from homozygous
parents
o Trait with ½ color ½ not means came from heterozygous
parents
Another method used to map out the human genes besides the
pedigree is the karyotype
Karyotype - a picture of all of the chromosomes in a cell
 Can show chromosomal changes or reveal a loss of a chromosome