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What is Genetics?
• Genetics: Study of heredity
• Heredity: passing of traits
from parent to child
• Patterns of relatedness can
help predict offspring
characteristics
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Autosomal recessive
Autosomal dominance
Sex-Linked
Incomplete dominance
Codominance
• “Father of Genetics”
• Famous for pea plant
studies
• Mendel studied seven
pea plant traits
– Color, shape, texture,
height, etc…
• Results shaped our
understanding of genetics
Each trait had a 3:1
ratio. No way that
can be a
coincidence!
• 1 gene may prevent
the expression of
another
• Organisms inherit 2
copies of each gene
– One from each parent
• Genes are located on chromosomes
• Genes inherited from mom and dad
• Genes come in several forms called
alleles
– Allele: Alternative forms of a
gene
– Ex: Flower color
• White allele or Purple allele
• Letters used to abbreviate alleles
– Dominant Allele = Capital letter
– Recessive Allele = Lowercase
letter
• Phenotype: Actual appearance of a gene
• Genotype: Genetic makeup of an organism
• Genotype determines phenotype
Genetics Vocabulary Review
Choices:
1) YY
2) Tall
3) Yy
4) SS
5) yY
6) gg
7) Smooth
8) Green
9) TT
10) Dwarf
Which choice(s) are examples of:
Genotypes?
1, 3, 4, 5, 6, 9
Phenotypes?
2, 7, 8, 10
Homozygous genotypes?
1, 4, 6, 9
Heterozygous genotypes?
3, 5
Homozygous recessive genotypes?
6
Homozygous dominant genotypes?
1, 4, 9
Punnett
Squares
• Defined: Tools used to
determine genetic
probability
• Probability = likelihood
that a certain event will
happen
• 2 Steps:
– 1) Place parent genotypes
on the outside of the box
– 2) Fill in the boxes
Cross a homozygous dominant yellow (YY) plant with
a homozygous recessive green (yy) plant
Key
Y = yellow
y = green
100%
Probability of growing a yellow plant? _____________
0%
Probability of growing a homozygous recessive plant? ____________
0%
Probability of growing a homozygous dominant plant? ____________
Cross a heterozygous dominant yellow (Yy) plant with a
heterozygous dominant yellow (Yy) plant
Key
Y = Yellow
y = green
50%
Probability of growing a heterozygous plant? ________
25%
Probability of growing a green plant? ________
25%
Probability of growing pure yellow? _________
Bravo! You can predict pea color!
So What?
Maria is a heterozygous healthy (Hh) female and Jeff
suffers from recessive cystic fibrosis (hh).
Key
H = healthy
h = cystic
fibrosis
Probability of having a healthy
50%
child? _________
Probability of having a homozygous
0%
dominant child? ________
Kobe Kuiz
1) How are dominant alleles expressed? Recessive?
2) Which of the following are genotypes? Phenotypes?
TT Green yY Pp Purple gg Smooth
3) Which of the following are heterozygous genotypes?
TT Green yY Pp Purple gg Smooth
4) Genes may often be found in two forms (dominant and recessive). What are
these alternate forms of a gene called?
5) Genes are segments of DNA found on _______________.
6) If item A is found in a 2:1 ratio compared to item B, what percentage is item A?
7) If item A is found in a 4:1 ratio compared to item B, what percentage is item A?
8) George & Martha are planning a family. Each has a family history of autosomal
recessive disorder and they agree to have their blood tested. George is found to
be heterozygous healthy and Martha is found to be homozygous dominant
healthy. What are the chances they have a healthy child? Homozygous
dominant child? Heterozygous child? Homozygous recessive child?