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What is the point of meiosis and
sexual reproduction?
Agenda for Jan 22nd
1. Go over test
2. Punnett Squares
Heredity
• What is heredity?
– The passing on of characteristics from parents to
offspring
• Genetics is the branch of biology that studies
heredity
– characteristics that are inherited are traits
• Mendel was the first to succeed in predicting
how traits would be transferred from one
generation to the next
Mendel
• Father of genetics
• Loved nature
• Austrian monk
– taught natural science
– worked on plant breeding experiments using pea
plants
• Developed basic understanding of genetics and
inheritance
Mendel’s Work
• Used pea plant
• He collected data for 10 years
• Large sample sizes;
– Results from 28,000 pea plants
• Published work but was dismissed
– Found later
Mendel’s Experiment
• P Generation – parent generation
• F1 generation – first filial generation, offspring
of parents
• F2 generation – second filial generation,
offspring of F1 generation
Grandparents
Parents
You
Collected
6022 yellow
and 2001
green
3:1 ratio
Mendel’s Results
P1
F1
F2
F2 ratio
smooth X
wrinkled seeds
all smooth
5474 smooth
1850 wrinkled
2.96:1
yellow X green
seeds
all yellow
6022 yellow
2001 green
3.01:1
axial X terminal
flowers
all axial
651 axial
207 terminal
3.14:1
red X white
flowers
all red
705 red
224 white
3.15:1
882 inflated
299 constricted
2.95:1
all green
428 green
152 yellow
2.82:1
all tall
787 tall
277 dwarf
2.84:1
inflated X
constricted pods
green X yellow
pods
tall X dwarf
plants
all inflated
3:1
ratio
Conclusions
1. Inheritance of traits are determined by "units"
or "factors" that are passed on to offspring
– called genes
– Different forms of a gene are alleles
Allele for purple flowers
Locus for flower-color gene
Homologous
pair of
chromosomes
Allele for white flowers
2. For each trait, an individual inherits one gene
from each parent
3. A trait may not show up in an individual but can
still be passed on
Rule of Dominance
• The trait that is observed in the F1 offspring is
the dominant trait (uppercase)
• The trait that disappears in the offspring is the
recessive trait (lowercase)
Law of Segregation
• The two alleles for a trait
must separate when
gametes are formed
– A parent randomly passes
only one allele for each trait
to each offspring
Law of Independent Assortment
• Random distribution of alleles during meiosis
Dominant and Recessive Genes
• Gene that prevents the other gene from “showing” –
dominant
• Gene that does NOT “show” even though it is present –
recessive
• Symbol – Dominant gene – upper case letter – T
Recessive gene – lower case letter – t
Dominant
color
Recessiv
e color
Dominant and Recessive
• Capital letters= dominant alleles
• Lower case letters = recessive alleles
• Two alleles for each trait
Which is better, dominant or recessive?
Homozygous (pure bred)
Organism with two of the same allele
HH
Homozygous dominant
hh
Homozygous recessive
Heterozygous (hybrid)
Organism with two different alleles
Hh
Rr
Dominant trait observed (notice the
dominant allele)
Genotype
Allele makeup of an individual
Tt
RR
TT
Rr
tt
rr
Phenotype
Observable characteristics of an individual
Flashcards
•
•
•
•
•
•
•
Phenotype
Genotype
Heterozygous
Homozygous
Allele
Diploid
Haploid
Predicting traits
• Monohybrid Crosses Provide information
about one pair of contrasting traits.
Parent’s Genotype
Parent’s Genotype
Law of Segregation
• Mechanism of gene transmission
Gametogenesis:
alleles segregate
Fertilization:
alleles unite
Parent’s 1 Genotype = Aa
Gametes =
Parent’s 2 Genotype = AA
Gametes =
Ratios:
Genotypes:
Homozygous dominant:Hetergozygous:Homozygous recessive
AA:Aa:aa
Phenotypes:
Dominant:recessive
Tall:short
Define the following:
Dominant, recessive, homozygous,
heterozygous.
Agenda for Friday Jan 23rd
1. Review
2. Punnett Square practice
Practice
A Tt (tall) plant is crossed with a Tt (tall plant).
1. What are the gametes formed by each parent?
2. What is the genotypic ratio?
A green pea sead (gg) is crossed with a hybrid
yellow seed (Gg). What will be the genotypic and
phenotypic ratios of the offspring?
A heterozygous plant (Tt) is crossed with short (tt)
plant.
What percentage of the offspring will be tall?
What percentage of the offspring will be short?
In guinea pigs, rough coats are dominant over
smooth coats. An Rr guinea pig is crossed with
an Rr guinea pig.
What are the chances of each genotype and
phenotype?
Agenda for Tuesday April 15th
1. Punnett Square practice
The punnett square shows the offspring of
two parents. What are the genotypes of
the parents?
Rr
Rr
rr
rr
Agenda for Thursday April 17th
1. Compare ratio lab
QUIZ WEDNESDAY
In pea plants, round (R) is dominant to
wrinkled (r). A heterozygous female is
crossed with a wrinkled male. What is the
probability (percent) of having an offspring
that is round?
Agenda for Tuesday April 22nd
1. Dihybrid crosses
Quiz tomorrow
Polyploidy
• Most cells are Diploid (2n)
• Some are polyploid
– One or more extra sets of
chromosomes
– Triploid – 3n
• Rarely occurs in animals
• Mostly plants
– Roughly 1 in 3 plants are polyploidy
• Increased vigor and size
Types of genetic crosses
• Monohybrid
– Mono = 1
– Cross looking at 1 trait
• Dihybrid
– Di = 2
– Cross looking at 2 traits
– Traits are not linked (do not affect each other)
– For example: round vs. wrinkled seeds and yellow vs.
green seeds
Dihybrid Cross
Making gametes
• Independent assortment – each allele distributes
randomly with the other
**more combinations than with a monohybrid
RrYy
Round (R) is dominant to wrinkled
Yellow (Y) is dominant to green
Cross a RRYy with a Rryy
What would the gametes look like
for a RrYy genotype?
Agenda for Wednesday April 23rd
1. TEST
Genetic Recombination
• New combination of genes produced by
crossing over and independent assortment
Why is genetic recombination important?
Gene Linkage
• Genes on same chromosomes are said to be
linked
– Travel together during Meiosis
• Not always true – crossing over occurs
• Genes further apart cross over more
frequently
– Make chromosome maps based on that info.
Chromosome Map
• Map genes A, B, C, D
– AB=3
– AD=4
– BD=7
AC=1
BC=2
CD=5
• Map genes A, B, C, D
– AD = 25
– CD = 15
– BC = 20
AB = 30
BD = 5