Download Chapter 11 Intro to Genetics

Chapter 11 Intro to Genetics
Genetics- study of heredity
Gregor Mendel
-Austrian monk
-studied science and math
-taught high school and in charge of the care of
monastery garden
-studied garden peas
-he knew that part of the flower produce pollen
-pollen contains male reproductive cells or sperm
-flower contains female reproductive cells or eggs
-Fertilization- process during sexual
reproduction, male and female cells join to form
a new cell
-new cell develops into a tiny embryo inside a seed
-Pea flowers are normally self-pollinating
-sperm cells fertilize the egg cells in the same flower
-seeds produced inherit all of the
characteristics from the parent plant= have
single parent
-Mendel had true-breeding pea plants
-if allowed to self-pollinate, produce
offspring identical to themselves
-Ex: tall, short, green seeds, yellow seeds
-Mendel wanted to produce seeds from 2
different plants
-He had to prevent self pollination
-cut male parts that produced pollen
-dusted pollen from another plant onto that
flower
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Cross-pollination- produced seeds that had 2
different parents
Mendel studied 7 different pea plant TRAITS
Trait- specific characteristic, varies from 1
individual to another
ex: seed color or plant height
Mendel crossed plants with certain characteristics and
studied their offspring
P generation= (parental)= original pair of plants
F1= “first filial” generation= offspring
filius and filia =”son” and “daughter”
Hybrids- the offspring of crosses between
parents with different traits
F1 hybrids
Mendel’s experiment showed that all of the offspring had the
character of only 1 of the parents, the character of the other
parent seemed to have disappeared
Mendel’s Conclusions:
1. Inheritance is determined by factors that
are passed from one generation to the next
genes- determines traits
genes control traits
alleles- different forms of a gene
2. Principle of Dominance- some alleles are
dominant and others are recessive
-dominant= always show trait
-recessive trait shown only when
dominant is not present
Where did the recessive alleles go? Did they disappear or
were they still present in the F1 generation?
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Allowed F1 generation to self-pollinate (crossed
F1 generation with itself) to produce F2
generation
Results: recessive traits had reappeared!
Segregation- separation of alleles during gamete
formation (gamete= sex cell)
Experiment overview: 2 parents- 1 tall, 1short
(tall= dominant)
F1= all plants tall
When each F1 plant flowers and produces gametes, the 2
alleles segregate from each other so that each gamete
carries only a single copy of the gene. Therefore, each F1
plant produces 2 types of gametes-those with the allele
for tallness and those with the allele for shortness.
figure 11-5
T=dominant allele; t= recessive allele
*11-2 Probability and Punnett Squares
Probability- likelihood that a particular event
will occur
ex: coin flip- 2 possibilities- heads up or tails up;
probability of either outcome are equal
-probability of heads up= 1 chance in 2 or ½ or
50%
-if you flip a coin 3x’s in a row, what is the
probability of heads up every time?
½ x ½ x ½ = 1/8
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1 in 8 chances of flipping heads 3x’s in a row
How is flipping coins related to genetics?
Segregation of alleles is completely random.
Punnett Squares- diagram used to predict and
compare the genetic variations that will result
from a cross.
Homozygous- have 2 identical alleles for a
particular trait; ex: TT or tt
Heterozygous- have 2 different alleles for a
particular trait; ex: Tt
Homozygous= true breeding
Heterozygous= hybrid
Phenotype= physical characteristics
Genotype= gentic makeup
Probabilities predict averages: need LARGE
sample
cannot predict precise outcome of individual event
-ex: flip coin twice= likely to get 1 head, 1 tail
-could also get 2 heads or 2 tails
-to be more likely to get the 50:50 ratio you need to
flip many times
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