Transcript Exam Review - Genetics FEDDEMA

EXAM REVIEW
Purpose: to create sex cells or gametes
WHAT IS MEIOSIS?

The process by which sex cells (gametes) are formed

Only occurs in reproductive cells (testes and ovaries)
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Produces gametes with half the number of chromosomes
HAPLOID (n) – 23 chromosomes instead of 46; (only gametes)
 DIPLOID (2n) – 46 chromosomes; normal cells
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
cells are divided twice without allowing for growth or
DNA duplication between divisions
Paired chromosomes similar in shape, size and
gene arrangement.
Why not identical chromosomes? Different Alleles
• Two rounds of cell division
• Meiosis I and Meiosis II
Meiosis I
• Prophase I
• Metaphase I
• Anaphase I
• Telophase I
• Cytokinesis
Meiosis II
• Prophase II
• Metaphase II
• Anaphase II
• Telophase II
• Cytokinesis
“Reduction
division”
- 46  23
chromosomes
“Separation
division”
Early
• Nuclear membrane begins to dissolve (disappear)
• Chromatin condenses to form chromosomes
• Centrioles begin to move to opposite poles
• Spindle fibres begin to form
Late
• Homologous chromosomes pair up forming
a tetrad
• Synapsis: the pairing of homologous chromosomes
• Crossing-over: Segments of the chromosomes may
be exchanged
• This leads to genetic diversity!
• Spindle fibres attach to the centromeres of the
chromosomes
• Chromosomes align at the equatorial plate in tetrad
form (in pairs)
• Spindle fibres shorten pulling homologous
chromosomes towards opposite poles
• Nuclear membrane reforms
• Spindle fibres break down
• Chromosomes begin to uncoil forming chromatin
Cytokinesis: division of cytoplasm forming two
daughter cells
Results after Meiosis I
• One cell  two cells
• 46 chromosomes (diploid)  23 chromosomes (haploid)
• One member of each homologous pair will be found in
each of the new cells
• The chromosomes in the two nuclei are NOT identical
• Homologous chromosomes are very similar, NOT
identical
• Crossing over adds to genetic variation
•
•
•
•
•
•
(No Interphase)
Nuclear membrane dissolves
Chromatin coils to form chromosomes
Spindle fibres begin to form
Centrioles move towards opposite poles
NO tetrad formation or crossing-over
• Spindle fibres attach to centromeres of
chromosomes
• Chromosomes align at the equatorial plate
• Centromere splits and sister chromatids move to
opposite poles
• Nuclear membrane reforms
• Spindle fibres break down
• Chromosomes uncoil to form chromatin
Cytokinesis: division of cytoplasm forming four
haploid gametes
Results after Meiosis II
• Two cells  Four cells
• Four HAPLOID daughter cells are produced
• Each contain 23 chromosomes
• The four haploid daughter cells all have unique genetic
information
• Random combo from mother & father
• Crossing over contributes to genetic differences
GAMETOGENESIS

gametogenesis

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formation of sex cells (sperm/egg) through the process of
meiosis
spermatogenesis
formation of sperm cells
 cytoplasm is divided equally between 4 sperm cells
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oogenesis
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formation of egg cells
cytoplasm is not divided equally
one egg cell receives most of the cytoplasm & all organelles
only one healthy egg cell is produced
three egg cells die (polar bodies)
GAMETOGENESIS
MITOSIS VS MEIOSIS
Mitosis
Meiosis
Function
produce cells needed for
growth, repair, asexual
reproduction
produce cells needed for
sexual reproduction
# of Divisions
1
2
Type of Cells
Produced
body cells (diploid – two
copies of all genes)
sex cells
(haploid – one copy of all
genes)
# of Daughter
Cells Produced
2
4
# of Chromosomes
in Daughter Cells
2n
n
WHY USE PEA PLANTS?
flowers have both male and
female reproductive organs
 plants can be self pollinated or
cross pollinated
 have many traits that can be
observed in 1 of 2 ways
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IMPORTANT GENETICS TERMINOLOGY:
Homozygous/Heterozygous

homozygous

individual that carries two of the same alleles for a
given characteristic/trait
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ex – two blue eyed genes (bb), two brown eyed genes (BB)
heterozygous

individual that carries two different alleles for a
given characteristic/trait
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ex – one blue eyed gene and one brown eyed gene (Bb)
GENOTYPE/PHENOTYPE

genotype

genetic makeup of an individual (ie the genes
someone carries)
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ex – an individual carries one blue eyed gene and one brown
eyed gene (Bb)
phenotype

outward appearance of the individual (ie. What they
look like)

ex – an individual has brown eyes
DOMINANT/RECESSIVE
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dominant allele
allele that is always expressed (seen) if it is present
 represented by a capital letter in genotype
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ex – brown eye allele (B)
recessive allele
allele that is expressed only if the dominant allele is
not present
 individual must be homozygous for the recessive
allele (ie. bb)
 represented by a lower case letter in genotype
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ex – blue eye allele (b)
Punnett Squares
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Diagram used to predict genotype and phenotype of offspring
Capital letter = dominant trait (eg. D)
Lower case letter = recessive trait (eg d)
If any capital letters are present the dominant trait will show
If 2 lower case letters are together, the recessive trait will show
Genotype
Phenotype
CC
Cleft chin
Cc
Cleft chin
cc
No cleft chin
MONOHYBRID CROSS
http://www.youtube.com/watch?v=xrDjN_4HKf0&feature=related
http://ed.ted.com/lessons/how-mendel-s-pea-plantshelped-us-understand-genetics-hortensia-jimenez-diaz
• Dominant allele masks the effects of a recessive
allele (RR, Rr- round)
• For recessive trait, need two copies of a recessive
allele (rr- wrinkled)
• It is possible to have more than 2 different alleles
for one gene
• There are many genes with multiple alleles
• Eg: hair colour (black, brown, blonde, red, etc)
• No longer use upper and lower case letters, use
capital letters with superscript letters or
numbers
• Eg Hair colour: Hb Hr
Example: Drosophila melanogaster (fruit fly)
• Many different eye colours are possible
• Red most common (wild type)
• Apricot, honey and white
• Creates a dominance hierarchy
Problem 1: What are the genotypes and phenotypes of
offspring from mating of the following Drosophila?
E1E4 (wild-type eye colour) x E2E3 (apricot eye colour)
• A condition in which neither allele for a gene
completely conceals the presence of the other, it
results in an intermediate expression of a trait
• Heterozygote exhibits a phenotype that is
somewhere between a dominant phenotype and a
recessive phenotype
• Eg: white snapdragon and red snapdragon
produce a pink snapdragon
Example: Snapdragons
Cross:
Red (CRCR)
x
White (CWCW)
Pink (CRCW)
Pink is an intermediate
phenotype between red
and white.
• Another type of incomplete dominance where
both alleles are expressed equally in a
heterozygote
• offspring with both alleles show a third
phenotype
• ex – red bull and white cow produce roan
calves (have both pure white hair and pure
red hair)
Example: Shorthorn cattle
Cross:
Red (HRHR)
x
White (HWHW)
Roan (HRHW)
Roan has intermingled white and red hair (exhibits
traits from both alleles)
BLOOD TYPES – CODOMINANCE AND DOMINANCE
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blood types show both codominance and dominance
three alleles are present
 type A allele – IA
 type B allele - IB
 type O allele - i
type A and B blood alleles are codominant (both are
expressed if an individual carries both)
type A blood alleles are dominant over type O blood
alleles (individual will express type A blood)
type B blood alleles are dominant over type O blood
alleles (individual will express type B blood)
Problem 5: What are the four different human blood
types?
Phenotype
Genotype
Type A
Type B
Type AB
Type O
IAIA, IAIO
IBIB, IBIO
IAIB
IOIO
a) A man has type O blood and a woman has type B
blood. If this couple has 6 children, all with type B,
what could you infer about the women’s genotype?
b) What are the genotypes and phenotypes of a man
with heterozygous A blood and a woman with O blood?
GREGOR MENDEL
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monohybrid crosses
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based on one characteristic, controlled by one gene
dihybrid crosses
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based on two characteristics controlled by two genes
• Inheritance of one gene is not affected by the
inheritance of another gene.
• During gamete formation, the two alleles for one
gene segregate or assort independently of the
alleles for other genes.
• Genes that govern pea shape are inherited
independently of the ones that control pea colour.
X- 2000 genes
Y- fewer than 100 genes
Sex-linked trait
• trait controlled by genes on the X or Y chromosome
TYPES OF INHERITANCE
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Autosomal inheritance
gene is found on an autosome
 both males and females are equally impacted by
disorders
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Sex-linked inheritance
gene is found on a sex chromosome
 males are impacted more often by these disorders as
they only have one copy of each chromosome
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http://www.youtube.com/watch?v=IJqFk-28G08
REPRODUCTIVE TECHNOLOGIES JIGSAW
Groups of 6; each member picks a topic:
 Prenatal testing, In-Vitro Fertilization, Gene
Therapy, Cloning, Selective Breeding, GMOs
 Research using the Chromebooks and share info
on the Google Docs

Reproductive
Technology
Explain
what it is
What are
possible
consequences?
What are
Position of
some ethical the Catholic
implications? Church?
EXAM REVIEW – GENETICS
Topics:
 Meiosis
 Label cells undergoing meiosis
 Heredity & Monohybrid crosses p. 139 #2, 3
 Multiple Alleles & Co-dominance p. 144 #2,3 p. 145 #2,3
p. 150 #7, p. 158 #11
 Sex-Linked Traits
 Dihybrid Crosses p. 154 #1, p. 159 #14
 Genetic technology
Review Questions:
Unit 2 Review
 Page 192 #3, 4, 5, 6, 7, 9, 10, 12, 20, 21,