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AP Biology
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Chapter 13-15
Next test December 6 
Study guide Corrections too
Chapter 13- Meiosis
• Heredity- or inheritance transmission of traits
from one generation to the next
• Genes- coded information with traits, segments
of DNA
• Gametes- reproductive cells (sperm and egg)
• Somatic cells- cells other than reproductive cells
• Locus- a specific location on a chromosome
• Asexual reproduction vs Sexual reproduction
• Life cycle- generation to generation sequence of
stages in reproductive history
Chromosomes
•
•
•
•
46 human chromosomes (somatic) 2n (2 sets)
Karyotype
Autosomes vs sex chromosomes
Haploid (n) – cells with a single chromosome set
• Fertilization- union of gametes (sperm and egg)
zygote is formed
• Zygote- fertilized egg, diploid because it contains
2 haploid sets from each parent
• Meiosis- process to form gametes, reducing
chromosome number by half
Meiosis
• Interphase
• Meiosis I
▫ Separates homologous chromosomes
• Meiosis II
▫ Separates sister chromatids
Meiosis I
• Prophase I
▫ Crossing over occurs
• Metaphase I
▫ Homologous chromosome PAIRS line up at
middle
• Anaphase I
▫ Duplicated homologous chromosomes separate
• Telophase I, Cytokinesis
▫ 2 cells result
Meiosis II
• Prophase II
• Metaphase II
▫ Homologous chromosomes (sister chromatids)
line up at center
• Anaphase II
▫ Sister chromatids separate
• Telophase II, Cytokinesis
Mendel and Gene Idea Chapter 14
• Blending hypothesis- genetic material mixes in a
manner which blends traits
• Mendel- peas
• Traits- characteristic inherited
• True-breeding – plants self-pollinate to have
same traits as parents
• Hybridize- cross (or cross-pollinate)
• P generation – parent
• F1 = Offspring of P
• F2 = offspring of F1
• Genotype –
• Phenotype –
• Alleles- alternative forms of traits
• Dominant• Recessive-
AP Biology
Mendel’s laws
• Law of segregation▫ 2 alleles for a heritable character separate during
gamete production (end up in different gametes)
• Law of independent assortment▫ Each pair of alleles segregates independently
during gamete formation.
Problem:
• Homozygous black rabbit mates with a
homozygous white rabbit
Phenotypic ratio:
Genotypic ratio:
Problem:
• Carry out a cross for the F1 generation:
Phenotypic ratio:
Genotypic ratio:
Problem:
• A brown tall rabbit is mated with a white short
rabbit. Brown and tall are dominant. Construct
a punnett square
Problem:
• Use F1 to determine the F2 generation
Laws of probability govern Mendelian
inheritance
• Probability of tossing heads with normal coin:
• Probability of rolling a 3 with a 6 sided die:
Law of multiplication
• Used to determine probability of two or more
independent events.
• Probability that 2 girls are born in a row to a
family:
• Probability that 6 girls are born in a row to a
family:
Law of addition:
• The probability of an event that can occur in two
or more mutually exclusive ways
• The probability of producing an F2 heterozygote:
Mendel genetics = simple genetics
• Incomplete dominance – intermediate offspring
• Codominance – both traits are shown
• Many genes exist in populations in more than
two allelic forms:
• ABO blood groups:
• IA, IB, i
• Pleiotrophic- when genes affect more than one
phenotypic characteristic
• Polygenic inheritance- additive effects of two or
more genes on a single phenotypic character.
Pedigrees
AP BIO
• Finish Chapter 15
• Lab Tuesday
• Test Thursday
AP Biology
• Thomas Morgan
▫ Worked with Drosophila (fruit flies)
▫ Discovered wild type – characteristic found in
nature
▫ Mutants were alternatives to the wild type
Fruit flies- carry eye color on X chromosome
White eyes – w
Red eyes – w+
Not All organisms are XX
and XY
SRY gene on Y
• SRY (sex-determining region of Y) gene was
discovered in 1990.
• Individuals with the SRY gene embryonic
gonads develop into testes
• Individuals without the SRY gene develop
ovaries
Genes located on Sex Chromosomes
• Sex-linked genes
• On Y = Y-linked genes
• On X = X-linked genes
▫ Color blindness
▫ Hemophilia
▫ Duchenne muscular dystrophy
Problem:
• Mother heterozygous for color blindness
• Father is not colorblind
Results:
Barr body
• Females inherit 2 X chromosomes, only 1 X
chromosome is active.
• Barr body- during development 1 X chromosome
per cell condenses into a compact Barr body.
• Barr bodies are not expressed.
Linked genes
• Linked genes – genes located near each other on
the same chromosome and tend to be inherited
together.
Crossing over
• Accounts for recombination of linked genes
• Occurs in prophase I meiosis I
• New combinations result in varied offspring
Alterations of chromosome number
• Nondisjunction –
▫ members of a pair of homologous chromosomes
do not separate properly during meiosis I
▫ Or sister chromatids fail to separate during
meiosis II.
▫ Trisomic, monosomic cells
▫ Polyploid – organisms with more than two
complete sets of chromosomes
Breakage of chromosome structure
• Deletion – when a chromosomal fragment is lost
• Duplication- occurs when a fragent becomes
attached as an extra segment to a sister
chromatid.
• Inversion – When chromosome fragment
reattaches to the original chromosome in the
reverse direction
• Translocation- fragment joins a non homologous
chromosome