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Chapter 11
Introduction
to Genetics
IV. MEIOSIS
• Mendel’s principles require 2 things1)each organism inherits a single copy for
every gene from each parent.
• 2)When an organism produces its own
gametes,those 2 sets of genes must be
separated from each other so that each
gamete has only 1 set.
AnalyzingGrabber
Inheritance
Interest
Section 11-1
• Offspring resemble their parents. Offspring
inherit genes for characteristics from their
parents. To learn about inheritance, scientists
have experimented with breeding various
plants and animals.
• In each experiment shown in the table on the
next slide, two pea plants with different
characteristics were bred. Then, the offspring
produced were bred to produce a second
generation of offspring. Consider the data
and answer the questions that follow.
I. The work of Gregor Mendel
•
_____________________=The scientific
study of heredity.
genetics
Parents
First Generation
Second Generation
Long stems  short stems
All long
787 long: 277 short
Red flowers  white flowers
All red
705 red: 224 white
Green pods  yellow pods
All green
428 green: 152 yellow
Round seeds  wrinkled seeds All round
5474 round: 1850 wrinkled
Yellow seeds  green seeds
6022 yellow: 2001 green
All yellow
• 1. In the first generation of each experiment,
how do the characteristics of the offspring
compare to the parents’ characteristics?
• 2. How do the characteristics of the second
generation compare to the characteristics of the
first generation?
A. Gregor Mendel’s Peas
–
–
–
Austrian monk whose statistical work w/ pea
plants yielded a greater understanding of
biological inheritance
He knew each flower produces pollen,containing
the male reproductive cells-sperm and female
portion produces egg cells.During sexual
reproduction,male and female cell join in
________-making a new cell that develops into
an embryo
Pea plants self-pollinating
fertilization
identical
– He started w/ true-breeding plants-meaning
that if they are allowed to self-pollinate,they
make offspring _________ to themselves.
•
•
•
•
1 group ____ plants
1 group ______
1 made only ______ seed
1 made ______ seeds
yellow
tall
short
green
• Mendel wanted to produce seeds from male and
female reproductive cells from 2 different
plants,preventing self-pollination by crosspollination,with 2 different plants as parents….This
allowed him to cross- breed characteristics
B. Genes and Dominance
•
•
•
Traits
Mendel studied different characteristics.
These characteristics are called
______________-such as seed or flower
color or height in humans
• Studied 7 traits-see p.264-and he studied
the offspring
• The offspring are called F1(“first
filial”…Filius and filia are Latin words for
son and daughter)
• __________________are the offspring of
crosses of parents w/different traits.
Mendel expected characteristics to blend-like
red+white=pink-This was not the outcome
hybrids
• 2 conclusions:
– 1) biological inheritance is determined by
factors carried by one generation to
another.we now call these chemical factors
that determine traits___________________.
• Different forms of a gene are called
___________________
genes
alleles
– 2) The Principle of Dominance states
some alleles are ________________and
some are recessive
• Alleles occur in pairs and only one allele w/ a
certain trait needs to be present for a
_________________trait
• 2 alleles of that trait must be present for
_______________traits.
• Tall plants were dominant and short recessive.
dominant
dominant
recessive
Figure 11-3 Mendel’s Seven F1 Crosses
on Pea Plants
Section 11-1
Seed Coat
Color
Pod
Shape
Pod
Color
Smooth
Green
Seed
Shape
Seed
Color
Round
Yellow
Gray
Wrinkled
Green
White
Constricted
Round
Yellow
Gray
Smooth
Flower
Position
Plant
Height
Axial
Tall
Yellow
Terminal
Short
Green
Axial
Tall
Principles of Dominance
Section 11-1
P Generation
Tall
Short
F1 Generation
Tall
Tall
F2 Generation
Tall
Tall
Tall
Short
Principles of Dominance
Section 11-1
P Generation
Tall
Short
F1 Generation
Tall
Tall
F2 Generation
Tall
Tall
Tall
Short
Section 11-1
P Generation
Tall
Short
Principles of Dominance
F1 Generation
Tall
Tall
F2 Generation
Tall
Tall
Tall
Short
Interest Grabber
Section 11-2
• If you toss a coin, what is the probability of getting
heads? Tails? If you toss a coin 10 times, how many
heads and how many tails would you expect to get?
Working with a partner, have one person toss a coin
• ten times while the other person tallies the results on
a sheet of paper. Then, switch tasks to produce a
separate tally of the second set of 10 tosses.
Tossing Coins
1.
2.
Assuming that you expect 5 heads and 5 tails in
10 tosses, how do the results of your tosses
compare? How about the results of your partner’s
tosses? How close was each set of results to what
was expected?
Add your results to those of your partner to
produce a total of 20 tosses. Assuming that you
expect 10 heads and 10 tails in 20 tosses, how
close are these results to what was expected?
3.If you compiled the results for the whole class,
what results would you expect?
4.How do the expected results differ from the
observed results?
C. Segregation
•
Mendel wondered if the recessive alleles
had disappeared or were they still present
in the F1 plants .He allowed all 7 kinds of
F1 hybrids to produce an F2 generation by
self-pollination
• F1 cross-recessive traits reappeared(~ ¼ F2 showed
recessive trait)
• Mendel said the alleles for tall and short
segregated(separated) during formation of sex cells
• Each gamete (Sex cell) carries a single copy of each
gene
• F1 produces 2 types of gametes-one has short allele
and one has tall allele.
• ______________letter stands for dominant allele and
lower case letter for
__________________.example:Tt T stands for tall
and lower case for short.
big
recessive
Probability and Punnett Squares
–
–
–
Likelihood for occurrence for a particular
event is __________________________ probability
PAST OUTCOMES DO NOT AFFECT
FUTURE OUTCOMES
Probability is used to determine genetic
occurrences using a diagram called a
___________________-which can predict
and compare genetic variations that will
result from a cross.
Punnett square
– ____________________means the organism
has the same 2 alleles for a trait---TT—also
called true-breeding
homozygous
– _______________means the organism has 2
different alleles for a certain trait---Tt-also
heterozygous
called hybrid.
– ______________is the observed physical
trait----example:tallness or shortness
– ________________=genetic makeup or
actual alleles----example:TT or Tt
genotype
phenotype
Section 11-2
Tt X Tt Cross
Tt X Tt Cross
Section 11-2
T
T
t
t
TT
Tt
tT
tt
1
2
Genotypes:___TT__Tt
1
_____tt
3
Phenotypes:____tall
_____short
1
– Each offspring will have the same probability
of a genotype and phenotype because each is
____________or a single occurrence
– Larger the # of offspring ,the closer
to_________________
–predicted
ratio.
segregated
III.Mendelian Genetics
• Mendel wondered if the segregation of one pr of
alleles affected another(?)
• A) Independent Assortment
– To answer his questions ,he performed a
______________.
• 1)Two-Factor Cross F1
– Crossed truebreeders w/ only round yellow peas
(genotype RRYY) x plants w/wrinkled green
peas(rryy)
– Offspring were round yellow,establishing the
dominance of RRYY
• Resulting genotype RrYy
2 factor cross experiment
rryy x RRYY
ry
ry
ry
ry
RY
RrYy
RrYy
RrYy
RrYy
RY
RrYy
RrYy
RrYy
RrYy
RY
RrYy
RrYy
RrYy
RrYy
RrYy
RrYy
RrYy
RrYy
RY
2) The Two factor Cross:F2
–
–
–
–
All F1 plants were ______.He wanted to see how
the alleles will segregate when F1’s are crossed
w/ each other to make an F2 generation
F2 produced 556 seeds-315 round 7 yellow and
32 were wrinkled and green
______seeds had a combination…Therefore
seed shape separated separately from color.
This is known as ______________________genes segregate independently during
formation of gametes.This accounts for much of
the variation in color
Heterogeneous
for seed shape
and color
209
The Principle of
Independent
Assortment
Summary of Mendel’s Principles
•
•
•
•
Inheritance of biological characteristics is
controlled by genes from the parents
When there are 2 or more alleles of a
gene,then one is dominant and one is
recessive
Most sexually reproducing organisms have 2
adults w/ 2 copies of each gene-one from each
parent.
Alleles usually segregate independently.
C. Beyond Dominant and
Recessive alleles
•
•
•
•
Exceptions to the rules
Majority of genes have more than 2 alleles.
Some are neither dominant nor recessive and
multiple genes and alleles or genes control traits
1 ) Incomplete dominance-one allele is not
completely dominant over another one
•
•
•
2) ____________-both alleles contribute to the
phenotype—example –in chickens the allele for black
feathers is codominant with white---this results in
__________offspring
3) _______________-more than 2 possible alleles
exist in a population(not in one organism-examplerabbits have 1 gene for coat color,but 4 possible
alleles for that gene….also an example is genes for
human blood type
4)_____________-traits controlled by 2 or more genes’
INTERACTION-4 different genes cover probably
control human skin color
CODOMINANCE
SPECKLED
MULTIPLE
ALLELES
POLYGENIC
TRAITS
Applying Mendel’s principles
–
_____________________started using fruit flies to study
genetics______________________________________They are easy
to study because they produce many offspring
quickly….Mendelian genetics applied to them
MORGAN
Drosophilia
melanogaster
E. Genetics and the Environment
– Traits not determined solely by genes
•
Traits determined by
____________________________
Interaction of the
genes and the
environment they
are in.
IV. MEIOSIS
• Mendel’s principles require 2 things1)each organism inherits a single copy for
every gene from each parent.
• When an organism produces its own
gametes,those 2 sets of genes must be
separated from each other so that each
gamete has only 1 set
Chromosome #
–
–
–
The sets of chromosomes will be
homologous,meaning that one from male
corresponds w/ one from female
A cell w/ both sets of homologous
chromosomes is _______________,meaning 2
sets(2N)---For Drosophilia,2N=8-2 complete
sets of chromosomes and 2 complete sets of
genes.
Gametes(sperm and egg cells),however contain
a __________________#-1 set of
chromosomes-for Drosophilia N=4.
haploid
diploid
• B.
Meiosis=___________________________
__________________________________
__________________________________
Process of reduction division in
which the number of chromosomes
per cell is cut in half through the
separation of homologous
chromosomes in a diploid cell
• 2 divisions-Meiosis I and Meiosis II
Meiosis I –
tetrad
• Chromosomes are replicated 1st
• Divide similar to mitosis,except in prophase I each
chromosome pairs w/ its corresponding chromosome to
make a __________________-which has 4 chromatids
• They exchange portions of their chromatids in
_______________________-resulting in a exchange
of alleles between homologous chromosomes and
produces new combinations of alleles.
• Homomlogous chromosomes separate and 2 new cells are
formed
• Each cell has 4 chromatids,but they are separated
Crossing-over
Meiosis II-
• No replication(of chromosomes) previous
to Meiosis II-unlike w/ meiosis I
• Each chromosome has 2 chromatids
• 4 daughter cells contain haploid # (N)
Figure 11-15 Meiosis
Section 11-4
Meiosis I
Go to
Section:
Figure 11-17 Meiosis II
Section 11-4
Meiosis II
Prophase II
Metaphase II
Anaphase II
Meiosis I results in two
The chromosomes line up in a The sister chromatids
haploid (N) daughter cells,
similar way to the metaphase separate and move toward
each with half the number of stage of mitosis.
opposite ends of the cell.
chromosomes as the original.
Go to
Section:
Telophase II
Meiosis II results in four
haploid (N) daughter cells.
•
•
•
•
•
Gamete Formation-In female- 1 egg cell
produced and 3 ______________________.
Male produces 4 sperm cells
D. Zygote=fertilized egg
E. Comparing Mitosis and meiosis
– Mitosis produces 2 genetically alike diploid
cells /also allows for growth
Meiosis produces 4 genetically different haploid
cells/for sexual reproduction ; (half the # of
C.
original chromosomes)/for sexual
reproduction;has 2 divisions(MI and MII)
Polar
bodies
V. Linkage and Gene Mapping
•
A. Linkage
–
•
Morgan in 1910 discovered the principle of
linkage-certain genes inherited together
Drosophilia had 4 linkage groups---CHROMOSOMES assort
independently,not the genes
B. Gene Maps
• .Crossing –over during meiosis separates
genes on the same chromosome onto
homologous chromosomes---This gives
great genetic ____________________.
diversity