Transcript Chapter 12 – Inheritance Patterns And Human Genetics

 Make a Punnett square for the following test cross: A
black hamster of unknown genotype is crossed with a
white hamster (aa). The offspring are 50% white.
 What was the genotype of the unkown black hamster?
Dominance relationships
 Heterozygotes have a
mixed phenotype
 Aa = pink
 Both genes are
expressed
 Aa = spotted
 More than 2 alleles of a
gene
 4 genes for rabbits
 C=agouti
Cch=chinchilla
Ch=himalayan
c=albino
 Dominance C > Cch >
Ch > c
 One allele hides the other
 One gene needed to “turn
on” another gene
 B = dark pigment
 b = light pigment
 E gene needed for color
 eebb= yellow fur
 Eabb= chocoalte fur
 Analyzed with a dihybrid
cross


Trait controlled by many genes
Continuous range of phenotypes
 Internal
 Hormones
 External
 Temperature,
nutrition, etc.
 Thomas Hunt Morgan
 Used fruit fly
 XX=female, XY= male
 Gene on X chromosome
 Males XY
 Often have disease
 Females XX
 Often carriers (heterozygous)
 Passed from mothers to sons
 “Skips a generation”
XR
XR Xr
XR
XR Xr
XR Y
XR Y
 Single allele traits (dominant)
 Huntington’s disease, dwarfism, cataracts
 Single allele traits (recessive)
 Albinism, cystic fibrosis, hereditary deafness
 Polygenic traits
 Hair/skin/eye color, foot size, nose length, height
 X-linked traits
 Colorblindness, hemophilia, muscular dystrophy
 Multiple allele traits
 ABO blood groups
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 Three alleles control
blood type: IA, IB, i
 Blood types are:
 A, B, or O
Genotype
Blood Type
IAIA
A
IAi
A
IBIB
B
IBi
IAIB
ii
B
AB
O
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 If A is blue and a is yellow, what will Aa be
if there is incomplete dominance? If
there is codominance?
 An XAXa female (normal) mates with a
colorblind (XaY) male. What percentage
of male offspring will be colorblind?
Female offspring?
 Punnett squares are helpful, but provide only
information on one generation at a time
 Pedigree analysis provides a pattern of inheritance
within a family grouping
 Phenotypes of family members are studied
 Rules for making a pedigree
1.) Circles are females; squares are males
2.) Horizontal lines represent marriage unions or linkage
between brothers & sisters
3.) Vertical lines represent offspring; offspring in order LR
oldestyoungest
4.) Filled in = infected, ½ filled in = carrier
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 Given the pedigree to
the left…
 How many males are
colorblind?
 How many females are
colorblind?
 How many females are
carriers?
 How many married
couples are shown?