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Chapter 9 - Introduction to Genetics

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Chapter 9 - Introduction to Genetics Genetics the branch of Biology that studies heredity how traits are passed on. AA aa ... – PowerPoint PPT presentation

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Title: Chapter 9 - Introduction to Genetics


1
Chapter 9 - Introduction to Genetics
  • Genetics the branch of Biology that studies
    heredity how traits are passed on.

2
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3
Chromosomes
  • Humans have 46 chromosomes arranged in 23 pairs
    (44 autosomes and 2 sex chromosomes)
  • Chromosomes are made up of DNA and Proteins
  • Chromosomes and therefore the DNA can be divided
    into genes
  • Genes are short segments of DNA

4
Chromosome with genes
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7
Allele alternate form of a gene
  • Example Brown/blue, tall/short
  • can be represented by a letter
  • Example Brown B
  • Blue - b

8
Homologous Chromosomes
Determines eye color
Genes
Determines hair color
9
Brown Allele
Blue Alleles
Blue Allele
b
b
b
B
One pair of your chromosomes for eye color
One pair of your chromosomes for eye color
10
Brown Allele
Blue alleles
Blue Allele
b
b
b
B
Homozygous alleles are the same
Heterozygous alleles are
different
11
Homozygous (pure)
  • The two alleles are the same
  • The two letters are the same
  • BB or bb
  • Homozygous Dominant BB
  • Homozygous Recessive - bb

12
Heterozygous (hybrid)
  • The two alleles are different
  • The two letters are different
  • Bb

13
Dominant Gene
  • A gene that will be expressed if it is present
  • Examples brown, tall, green, purple
  • Written as a capital letter

14
Recessive Gene
  • A gene that will only be expressed if there are
    two alleles present
  • Recessive genes are not expressed if there is a
    dominant gene present
  • Short, blue, yellow, white
  • Written as a lower case letter

15
Genotype
  • The two alleles an organism has
  • What the genes say
  • Ex. BB, Bb, bb

16
Phenotype
  • Physical appearance of an organism
  • The result of the expression of the genes
  • Example tall, short, brown, blue

17
The Goal
  • The goal of genetics is to determine the possible
    offspring that can be produced from two parents
  • The likelihood of an outcome is determined
    through the laws of probability

18
Probability
  • The likelihood that a specific event will occur
  • Can be expressed as a decimal, percent or a
    fraction

19
Equation for Probability
Number of times an event is expected to happen
Probability
The number of opportunities for an event to happen
20
Probability Example
  • You flip a coin once
  • The probability of getting tails is ½
  • You flip a coin twice
  • The probability of getting tails twice is 1/4

1
1
1

X
4
2
2
21
T
H
or
First Flip
Second Flip
If I got Tails on the first flip I can either get
heads or tails On the second flip
H
T
22
Second
Probability of getting
First
H
1/4
H
T
1/4
H
1/4
T
T
1/4
23
Gametes
  • Egg or sperm
  • Haploid
  • Contains half the number of chromosomes
  • One gene from each homologous pair

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Early Ideas on Heredity
  • Until the 19th century it was thought that the
    reason people look like their parents is because
    they were a blend of both parents.
  • The work of Gregor Mendel changed the views of
    how characteristics are passed on from 1
    generation to the next.

26
Gregor Mendel
  • Born in 1822 in Austria
  • Studied at the University of Vienna
  • Became a priest and lived in a monastery
  • He was in charge of the garden and he studied pea
    plants

27
Gregor Mendel
  • Pea flowers have both male and female parts
  • They normally produce seeds through
    self-pollination
  • The pollen from the male flower part fertilizes
    the egg from the female flower part of the same
    flower
  • These seeds would inherit all their
    characteristics from the single plant that bore
    them

28
Gregor Mendel
  • Mendel figured out that self-pollination could be
    prevented
  • He cut the male parts off of 1 plant and the
    female parts off another plant
  • Then he pollinated the 2 plants by dusting the
    pollen from one onto the flower of the other
  • This is known as cross-pollination
  • Produces seeds with the characteristics of both
    plants

29
Gregor Mendel
  • Mendel had a stock of peas that were purebred
  • They would only produce offspring that were
    identical to them
  • He decided to cross plants with different
    characteristics to produce hybrids
  • He studied a few isolated characteristics to
    simplify his experiments

30
Gregor Mendel
  • Pea Traits Studied

Seed Shape Seed Color Seed Coat Color Pod Shape Pod Color Flower Position Plant Height
Round Yellow Gray Smooth Green Axial Tall
Wrinkled Green White Constric-ted Yellow Terminal Short
31
Genetic Crosses
  • When doing genetic crosses it is important to
    keep tract of the generations
  • P1 parents
  • F1 children of the parents (P1)
  • F2 Children of the F1s

32
GG
gg
Gg
gg
GG
Gg
33
A Genetic Cross


Punnett Square used to predict the possible
outcomes of a cross
34
AA
aa
aa
Male produces one type of sperm with the gene A
Female produces one type of egg with the gene a
35
The Baby Elephants will be..
Aa
Aa
Aa
Aa
36
Monohybrid Cross
a
a
Aa Aa
Aa Aa
A
A
37
How to fill in the Punnett Square
38
Monohybrid Cross
  • Cross where one trait is looked at
  • Dark elephant vs. light elephant

39
Aa
Aa
Male produces two types of sperm with the gene A
or a
Female produces two type of eggs with the gene A
or a
40
The Baby Elephants will be..
Aa
AA
aa
Aa
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42
Genotypic Ratio
  • Ratio of the offspring's genotypes

Genotypic Ratio 121
EE 1 Ee 2 ee 1
43
Phenotypic Ratio
  • Ratio of the offspring's phenotypes

Phenotypic ratio 31
3 smooth 1- wrinkled
44
Phenotypes?
Genotypic Ratio?
Genotypes?
Phenotypic Ratio?
45
Law of Segregation
  • A pair of genes is segregated or separated during
    the formation of gametes

46
Law of Independent Assortment
  • Genes for different characteristics are not
    connected
  • They are inherited independently

47
Dihybrid Cross
  • A cross between individuals that involves two
    pairs of contrasting traits
  • Look at hair color and eye color at the same time
  • Look at height and color at the same time

48
Dihybrid Cross Punnett Square




49
AABB
aabb
AB
ab
ab
AB
AB
AB
ab
ab
50
Sperm
Egg
AB
ab
Fertilization
AB ab
AaBb
Genes in the fertilized egg
51
ab
ab
ab
ab
AaBb AaBb AaBb AaBb
AaBb AaBb AaBb AaBb
AaBb AaBb AaBb AaBb
AaBb AaBb AaBb AaBb
AB
AB
AB
AB
52
AaBb
Genotypic Ratio 1 Phenotypic Ratio 1
53
What if the Dihybrid cross has heterozygous
parents?
  • How do you find the gametes?

54
How to find genes for the gametes of
a dihybrid cross
B
AB
A
b
Ab
aB
B
a
b
ab
55
AaBb
AaBb
AB
Ab
AB
Ab
aB
ab
ab
aB
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59
Dihybrid Heterozygous Cross Genotypic Ratio
121242121
60
Testcross
  • When an individual of unknown genotype is crosses
    with a homozygous recessive individual
  • B? x bb

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The End
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