Heredity and Genetics

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Heredity and Genetics
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PRINCIPLES OF GENETICS

• OVERVIEW
• Like produces like, but not exactly like

REVIEW Sexual reproduction ? variation due to
chromosomes
HEREDITY transmission of traits from parents
to offspring GENETICS science of heredity
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1. A History Lesson

Gregor Mendel 1822-1884 monk in monastery _at_
Czechoslovakia Vienna- studied science and
math- became a teacher 2 yrs later- returned to
monastery plant experiments 1866- published
data from 8 years of experiments 1900- finally
genetics recognized as major development
Mendels Experiments Studied pea plants (b/c
clearly express traits like flower color, seed
shape, seed color, and plant height)
large sample sizes- help ensure actual ratios
present in population
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crossed different plants ? ex. Purple flowers
x white flowers
offspring of parental cross first filial
generation (F1) offspring of 2nd cross 2nd
filial generation (F2)
Mendel produced 929 offspring 705 were purple
(31 ratio)
DOMINANT TRAIT form of a trait that dominates
another trait (prevents expression of another
trait) (ex. Purple flowers) appears in F1
generation
RECESSIVE TRAIT hidden in F1 generation
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MENDELS HYPOTHESIS Mendels experiments saw
recessive trait disappear in F1 generation but
reappear in F2 generation ASSUMPTION for each
trait, there must be a pair of factors- 1 comes
from egg 1 from sperm
Factors GENES contain information for
every trait Represented by symbols or
letters Capitals dominant lowercase
recessive
EX. W purple, w white
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ASSUMPTION 2 genes segregate during gamete
formation offspring ratio depending on genes
present
EX. WW x ww parents Ww Ww Ww Ww F1 Ww x
Ww WW Ww Ww ww F2 RESULTS 1WW 2Ww 1ww
3 purple 1 white (similar to 705 929)
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EASIER TO SEE WITH PUNNETT SQUARES Chart used
to determine possible combinations of genes among
offspring
Gametes of 1 parent


Gametes of 1 parent
W w
EX Ww x Ww
WW Ww
Ww ww
W w
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TEST OF SEGREGATION 31 ratio 1st time but
what if Ww x ww???
MAKE YOUR PUNNETT SQUARE
W w


w
ww
Ww
50 white 50 purple!!!
w
Ww
ww
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GENETICS TERMINOLOGY
ALLELE either of 2 alternative forms of gene
for particular trait ex. W or w
GENOTYPE combo. of alleles for certain
trait ex. WW, Ww, or ww
PHENOTYPE appearance of trait ex. purple
or white
HOMOZYGOUS 2 of same alleles for given
trait ex. RR, rr (deals w/ seed shape) or WW
or ww
HOMOZYGOUS DOMINANT 2 dominant alleles
(WW) HOMOZYGOUS RECESSIVE 2 recessive alleles
(ww)
HETEROZYGOUS 2 different alleles for a
trait ex. Rr or Ww
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Pedigree charts
are used to help determine the possible
genotypes of parents and offspring
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karyotypes
are used to analyze the chromosomes present in a
person
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TIME TO PRACTICE PUNNETT SQUARES!!