Download Chapter 8 - Central Lyon CSD

Chapter 8
Heredity
Terminology
 Allele – each alternative form of a gene for a certain trait
 Genotype – combination of alleles for a given trait
 Phenotype – appearance of a trait as determined by a given
genotype
 Homozygous – same alleles
 Heterozygous – different alleles
Don’t write
any of this
down. Just
listen.
Principles of Genetics
 Like produces like but…………
 In this chapter we will find out why…
 Heredity
Genetics: the science of heredity.
Write this
 Origins of genetics
But not this
 Gregor Mendel
 In 1866 he published the results of 8 years of experiments and
analysis.
Mendel worked with the common pea plant.
 Grows easily
 Produces many offspring in a short amount of time
 Certain varieties have sets of clearly different characteristics that remain
unchanged generation to generation.
Mendel found that these traits are hereditary
Just keep listening.
 Mendel wanted to determine how these traits were transmitted.
 Used good science.
 Was looking for general trends to form a basic set of rules about
the transmission of traits.
 Chose 7 traits.
Mendel’s results. Now take notes.
 Pea plants reproduce sexually. Both male and female sex organs
are in the same flower and they usually self fertilize. This makes
a pure plant. They always look the same.
 Mendel crossed plants with opposite traits
 Purple flowers with white flowers, both directions
 Pollen transfer
Mendel found that all offspring yielded purple flowers.
Keep writing.
 Offspring of a parental cross are called the first filial or _______
generation.
 He then let these plant reproduce normally.
 Offspring of the 2nd cross are called the second filial or _______
generation.
 The results were very revealing:
 Of the 929 offspring, 705 were purple and 224 white – a ratio of 3
to 1.
What do the results tell us?
 Mendel noted that for each trait one __________________
the other.
 Purple is dominant.
The other trait disappears in the F1 generation and is called
…_________________.
Mendel’s hypothesis: each pea plant is the result of the union of an
egg and a sperm so each trait must have a pair of factors (we now
call them genes).
Genes
 Mendel labeled each gene with a letter. Capital for dominant
and lower case for recessive.
 Flower color in peas: W for purple and w for white
Remember, when egg and sperm unite there are 2 genes for each
trait.
Gene Segregation
 The original plants in Mendel’s experiments were pure.
 WW for purple
 ww for white
When crossed they offspring would all be Ww – one gene from each
parent. This represents the F1 generation.
F2 generation
 When 2 of the F1 generation are crossed you get the F2
generation – 3 possibilities
 WW
 Ww
 ww
The chances of Ww combining are twice as likely as the other
possibilities.
Punnett Squares
 The chart used to determine possible combinations of genes
among offspring is the
 Punnett Square
Top – genes from one parent
Side – genes for other parent
Inside – all combinations
The test of segregation.
 Mendel predicted that if the F1 generation was paired with white
– flowered plants there would be new results. He was right. He
predicted 50/50
Principle of Segregation
 During gamete formation the pair of genes responsible for
each trait separates so that each gamete receives only one
gene for each trait.
 Gametes unite to produce predictable ratios of traits among
offspring.
Principle of Independent Assortment
 Genes of different traits segregate independently during
gamete formation
Two trait problem
 RrYy x RrYy
Two trait problem
 In guinea pigs rough coat is dominant – R
 Black color is dominant – B
 Cross a heterozygous black- smooth coated male and a
heterozygous black rough coated female